10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

31 May 2020, 07:00 → 5 Jun 2020, 18:00 US/Central

Online

Christina Markert (University of Texas at Austin (US)), Claudia Ratti (University of Houston), Frank Geurts (Rice University (US)), Rainer Fries (Texas A&M University)

Important Update:

• Proceedings deadline extended to September 6, 2020

• Conference photos are available

The organizers strongly endorse the APS Board Statement on Racial Violence:

Physics flourishes best when physicists can work in an environment of safety, justice, and equity. Therefore, all of us must work vigorously against systemic racism and to overcome implicit biases. The Board of the American Physical Society believes that it is timely to reaffirm the importance of building a diverse and inclusive physics community, as expressed in the APS Joint Diversity Statement (Human Rights 08.2). The Board expresses deep concern over incidents of racially biased violence and threats of violence against people of color.

PHOTOGRAPH BY KEREM YUCEL, AFP/GETTY

 

The 10th edition of the Hard and Electromagnetic Probes International Conference series will be hosted as an online conference from June 1st until June 5th 2020, with a student day on May 31st. The conference is focused on experimental and theoretical developments on perturbative probes of hot and dense QCD matter as studied in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions. Specifically, topics for discussion will include:

• Nuclear PDFs and hard processes in nuclei
• Early time dynamics
• Jets and their modification in QCD matter
• High momentum hadrons and correlations
• Heavy quarks and quarkonia
• EM and electroweak probes
• Future experimental facilities
• New theoretical developments

 

COVID19 follow-up.pdf

COVID19 statement.pdf

First_Circular.pdf

Hard_Probes_2020_Poster.pdf

HardProbes2020.zip

HP2020 - All Zoom Room Links - J links.pdf

HP2020 Online Announcement.pdf

HP2020 Poster Zoom Rooms.pdf

Second_Circular.pdf

Third_Circular_Indico.pdf

Sunday 31 May

Student Lectures: I

Student Lectures

Convener: Sevil Salur (Rutgers State Univ. of New Jersey (US))

1 Student Day Welcome

Speakers: Ivan Vitev, Sevil Salur (Rutgers State Univ. of New Jersey (US))

2 Initial State Physics

Speaker: Renaud Boussarie (Brookhaven National Lab)

BoussarieHP2020.pdf

Recording

3 Electroweak Probes

Speaker: Takao Sakaguchi (BNL)

EWprobes_HP2020_Lecture_Posted.pdf

Recording

09:10 Break

Student Lectures: II

Student Lectures

Convener: Sevil Salur (Rutgers State Univ. of New Jersey (US))

4 Jets: Theory

Speaker: Ivan Vitev

LectureHP2020.pdf

Recording

5 Jets: Experiment

Speaker: Olga Evdokimov (University of Illinois at Chicago (US))

2020_HPStudentDay_Evdokimov.pdf

Recording

10:55 Break

Student Lectures: III

Student Lectures

Convener: Ivan Vitev

6 Open Heavy Flavor

Speaker: Ralf Rapp (Texas A&M University)

hp20.pdf

hp20.ppt

Recording

7 Quarkonia

Speaker: Manuel Calderon De La Barca Sanchez (University of California Davis (US))

MCBS-QuarkoniumAA-HP20.pptx

MCBS-QuarkoniumAA-HP20-ReducedSize.pdf

12:55 Break

Student Lectures: IV

Student Lectures

Convener: Elena Caceres (University of Texas - Austin)

8 String Theory and QCD

Speaker: Saso Grozdanov (MIT)

Grozdanov_HP2020.pdf

Recording

9 EIC Physics Overview

Speaker: Prof. Bernd Surrow (Temple University)

BSurrow-EIC-Lecture-HardProbes2020.pdf

Recording

Monday 1 June

Plenary: Experimental Overview I

Plenary

Convener: David d'Enterria (CERN)

10 Welcome

Speakers: Christina Markert (University of Texas at Austin (US)), Claudia Ratti (University of Houston), Frank Geurts (Rice University (US)), Rainer Fries (Texas A&M University)

Recording

Welcome.pdf

11 ALICE Overview

Speaker: Dr Yaxian Mao (Central China Normal University CCNU (CN))

Recording

YMao_HP2020_Online20200601_final.pdf

12 ATLAS Overview: Recent Results and Future Plans

Speaker: Dominik Karol Derendarz (Polish Academy of Sciences (PL))

HP2020_derendarz_vf.pdf

Recording

13 CMS: Recent Results and Future Plans

Speaker: Prof. Daniel Tapia Takaki (University of Kansas)

DTT - HP - slides v20.pdf

Recording

09:15 Break

Plenary: Experimental Overview II

Plenary

Convener: Sevil Salur (Rutgers State Univ. of New Jersey (US))

14 LHCb: Recent Results and Future Plans

Speaker: Cesar Luiz Da Silva (Los Alamos National Laboratory (US))

HardProbes2020-Cesar.pdf

HardProbes2020-Cesar.pptx

Recording

15 STAR Overview

Speaker: Zaochen Ye (Rice University)

Recording

STAR_Highlights_HP2020_ZaochenYe_final.pdf

16 PHENIX Overview

Speaker: Marzia Rosati (Iowa State University (US))

Recording

rosati-hp2020.pdf

10:45 Break

Parallel: A1 - Jets and High-PT Hadrons I

P2

Convener: Carlos Albert Salgado Lopez (Universidade de Santiago de Compostela (ES))

17 Single jet and dijet measurements of jet quenching with the ATLAS detector

High energy partons are known to lose energy when passing through the hot and dense medium produced in heavy-ion collision. This results in a modification to the transverse momentum distributions of both charged hadrons and jets. It has been previously shown in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$~TeV that parton energy loss within the Quark Gluon Plasma results in significant modifications to the transverse momentum balance of dijet pairs. More differential measurements are needed to better understand the path length dependence, the role of fluctuations in the energy loss, and the energy redistribution. This talk presents the latest results on the fully unfolded dijet momentum balance in Pb+Pb and $pp$ collisions at $\sqrt{s_{NN}} = 5.02$~TeV, as well as measurements in Xe+Xe collisions at $\sqrt{s_{NN}} = 5.44$~TeV with the ATLAS detector at LHC. The dijet momentum balance is measured as a function of the azimuthal angle with respect to the event plane. This talk will present also a measurement of the single jet yields as a function of the azimuthal angle with respect to the event plane in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$~TeV. In addition, charged-hadron nuclear modification function will be presented in Pb+Pb and Xe+Xe systems with detailed comparisons between the two collision systems. These measurements provide new information about the path-length and system-size dependence of jet energy loss within the medium.

Speaker: Virginia Bailey (Univ. Illinois at Urbana Champaign (US))

HPTalk_ATLASJets_VBailey_v2.pdf

Recording

18 Measurement of fully-reconstructed inclusive jet production in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV by the STAR experiment

The STAR Collaboration at RHIC reports the measurements of both charged and fully-reconstructed inclusive jet production in central (0-10\%) and peripheral (60-80\%) Au+Au collisions at $\sqrt{s_{\scriptsize{\textrm{NN}}}}$ = 200 GeV. The charged jet analysis utilizes a dataset corresponding to 70 $\mu\mathrm{b}^{-1}$ recorded in 2011, while the new fully-reconstructed jet analysis utilizes a dataset corresponding to 184 $\mu\mathrm{b}^{-1}$ recorded in 2014. Both datasets were recorded using a Minimum Bias trigger. Jets are reconstructed using charged-particle tracks in the Time Projection Chamber and neutral energy measured by the Barrel Electromagnetic Calorimeter with $p_{\scriptsize{\textrm{T}}}$($E_{\scriptsize{\textrm{T}}})>$ 0.2 GeV/$c$ (GeV). Jet reconstruction is carried out using the anti-$k_{\scriptsize{\textrm{T}}}$ algorithm with resolution parameter $R$ = 0.2, 0.3 and 0.4. The large background yield to the jet signal in heavy ion collisions is suppressed by requiring high-$p_{\scriptsize{\textrm{T}}}$ leading charged or neutral radiation in accepted jet candidates. The bias imposed by this requirement is assessed, and the $p_{\scriptsize{\textrm{T}}}$-region in which this bias is negligible is identified. Charged jet and fully-reconstructed jet inclusive distributions are reported in central and peripheral Au+Au collisions for $p_{\scriptsize{\textrm{T}}}^{jet}>$10 GeV/$c$. Yield suppression, corresponding to medium-induced parton energy loss, is observed for central Au+Au collisions relative to both peripheral Au+Au collisions and vacuum reference. Medium-induced jet broadening is measured using the $R$-dependence of yields. The results are compared to jet measurements at the LHC and theoretical calculations.

Speaker: Robert Líčeník (Nuclear Physics Institute, Czech Academy of Sciences)

InclusiveJets_RL_HP_final.pdf

InclusiveJets_RL_HP_v24.pdf

Recording

19 Jet fragmentation in a dense medium from perturbative QCD

We study the fragmentation of an energetic jet propagating through a
dense quark-gluon plasma within perturbative QCD. We use a recently developed factorisation scheme (and the associated Monte-Carlo generator), in which the standard vacuum-like parton branchings are factorised in time from the medium-induced emissions triggered by multiple soft scattering in the medium. Besides the Monte-Carlo results, we present analytic calculations based on piecewise approximations which render the physical interpretation transparent. Our results for the nuclear modification factor for the jet fragmentation function are in qualitative agreement with the experimental data in Pb+Pb collisions at the LHC. In particular, we reproduce the enhancements seen in the data at both relatively soft and relatively large transverse momenta, with clear physical interpretations. The perturbative predictions however are quite sensitive to the value of the infrared cutoff (the confinement scale), due to the fact that the fragmentation function is not an infrared safe quantity. To remedy this, we propose a new observable --- the (primary) subjet fragmentation function --- which is infrared safe and has features similar to the fragmentation function. We provide predictions for this observable that could be tested against the experimental data.

Speaker: Paul Caucal (IPhT)

HP2020-caucal.pdf

Recording

20 Full solution of the medium-induced radiation spectrum

New measurements of jet quenching observables at RHIC and at the LHC, such as jet substructure observables, demand an increased precision in the theory calculations describing medium-induced radiation of gluons. Closed expressions for the gluon spectrum including a full resummation of multiple scatterings have been known for the past 20 years, but have only been evaluated in specific limits either taking a few terms in an opacity expansion or by employing a gaussian approximation for the interaction potential — which misses important physical effects. We present here a new flexible method to compute the full spectrum for a realistic interaction potential, thus allowing us for the first time to properly quantify the effect of the all-order resummation of multiple scatterings. This new approach paves the way for precision phenomenological studies including multiple scattering effects such as coherence phenomena.

Speaker: Carlota Andres (Jefferson Lab)

HP2020.pdf

Recording

21 Measurement of jet nuclear modification factor with large radius in PbPb collisions at 5.02 TeV with the CMS experiment

Partons are colored probes that interact with the quark-gluon plasma (QGP). By studying jets, the observable final state product of partons, we can improve our understanding of the interaction mechanism between partons and the QGP. Jet nuclear modification factor (RAA) is a simple yet profound observable that measures the amount of suppression with respect to a reference of proton-proton collisions at the same nucleon-nucleon center-of-mass energy. CMS has measured, for the first time in heavy-ion collisions, the RAA for inclusive jets up to a resolution parameter of 1.0, with PbPb data collected at 5.02 TeV. The result complements well both the traditional jet observables and jet substructure observables.

Speaker: Christopher Mcginn (Massachusetts Inst. of Technology (US))

hp2020_CMSJetRAA_CFM_20200601.pdf

Parallel: A2 - Electroweak Probes I

Convener: Prof. Dinesh Srivastava (National Institute of Advanced Studies, Bengaluru)

22 Electroweak probes in heavy-ion collisions with ATLAS

Electroweak bosons produced in lead-lead (Pb+Pb) collisions are an excellent tool to constrain initial-state effects which affect the rates of hard-scattering processes in nucleus-nucleus interactions. The production yields of massive electroweak bosons, observed via their leptonic decay channels, offer a high-precision test of the binary collision scaling expected in Pb+Pb and a way to quantify nuclear modifications of the parton distribution functions (PDFs).
The large samples of Pb+Pb data at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV collected by the ATLAS experiment in 2015, and the corresponding high-statistics $pp$ data at the same collision energy used as a baseline, allow for a detailed experimental study of these phenomena and comparisons to predictions from a variety of theoretical calculations. This talk presents the latest ATLAS results on electroweak boson production, including updated results on Z production and high-precision W boson results in Pb+Pb collisions. Inclusive production of prompt photons in proton-lead~($p$+Pb) collisions at $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV is also covered.
Various predictions of nuclear modifications to PDFs are discussed.

Speaker: Iwona Grabowska-Bold (AGH University of Science and Technology (PL))

HardProbes2020-EWBosonsAtlas-062020.pdf

New light-by-light measurement

Recording

23 Illuminating the early stages of relativistic heavy-ion collisions: the pre-hydro phase as seen through photons and hadrons

We model relativistic heavy-ion collisions with a hydrid dynamical approach which consists of an IP-Glasma initial state followed by a phase modeled by an effective QCD kinetic theory [1]. This then leads into viscous hydrodynamics and finally transport theory (MUSIC + UrQMD) [2]. The system's complete energy-momentum tensor -- including the shear and bulk viscous components -- is followed through these different stages. The effect of the pre-hydro phase on the spectra and flow coefficients of photons and hadrons is highlighted. We study how that non-equilibrium phase influences the hadron and photon flow coefficients in Pb+Pb, Xe+Xe, and O+O collisions at 5 TeV. Because the space-time volume scales differently from the number of binary collisions from O+O to Xe+Xe and Pb+Pb collisions, a systematic system size comparison of photon production can further shed light on the relative contributions from thermal and prompt sources and provide further insight into early time QGP dynamics. We also explore the effect of early chemical equilibrium on the photon observables.

[1] A. Kurkela, A. Mazeliauskas, J.F. Paquet, S. Schlichting, and D. Teaney, "Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory," Phys. Rev. Lett. 122, no. 12, 122302 (2019); "Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions," Phys. Rev. C 99, no. 3, 034910 (2019)

[2] S. McDonald, C. Shen, F. Fillion-Gourdeau, S. Jeon and C. Gale, "Hydrodynamic predictions for Pb+Pb collisions at 5.02 TeV", Phys. Rev. C 95, no. 6, 064913 (2017)

Speaker: Jean-Francois Paquet (Duke University)

hp2020_jfpaquet.pdf

Recording

24 Photon emission at hadronization from quark-gluon plasma

We investigate photon emission at the hadronization stage of high-energy heavy-ion collisions.
According to coalescence/recombination models for hadronization from a quark-gluon plasma (QGP),
quarks and antiquarks closely locating in the phase space are assumed to suddenly form a hadron.
Transition from free quark/antiquark states to hadrons (bound states of quarks or antiquarks) is,
however, an energy violating process, and should be accompanied by emission of other particles
to compensate the energy difference between the initial and final states.We consider the case where the additional particle is a photon, which is an analog of the “radiative recombination,” a well-known process in plasma physics. The radiative recombination, such as $e^−$ + $p^+$ → H$^0$ + $\gamma$, occurs when
an electromagnetic plasma goes back to an atomic gas. When a QGP hadronizes, we expect similar processes, such as $q$+$\bar{q}$ $\rightarrow$$\pi^0$ +$\gamma$, to take place. As a simplest and phenomenological realization of the radiative recombination for hadronization, we modify the recombination model so that the energy is conserved by the introduction of photon emission. Our “radiative hadronization” picture which is realized by this simple model has the following properties: (i) it brings about enhancement of the photon yield, (ii) radiated photons flow similarly as hadrons, and (iii) the $p_T$ distribution of emitted photons mimics thermal distribution whose effective temperature is given by blue-shifted quark’s temperature. We also present numerical results combined with a hydrodynamic model on the pT spectrum and elliptic flow parameter of the photon at RHIC and LHC energies.

Speaker: Chiho Nonaka (Nagoya University)

hp2020_nonaka.pdf

Recording

25 PHENIX results on direct photon production from Au+Au collisions

PHENIX measurements of low $p_T$ direct photons in Au+Au collisions at 200
GeV show large yields that have simultaneously a large anisotropies with
respect to the reaction plane, and that scale with the charged multiplicity
to a power of 5/4, independent of  transverse momentum and collision
centrality. Calculations of thermal photon emission fall short in describing
these three features. Furthermore, a recent publication of the STAR
collaboration indicates lower direct photon yields in Au+Au collisions than
observed by PHENIX.  In order to provide new PHENIX has shown first results
from Au+Au data taken in 2014. These data have 10 fold statistics compared
to published results. In this talk we will show the latest direct photon
results from this data set.

Speaker: Veronica Canoa Roman

HP2019_Dphotons.pdf

Recording

26 Isolated photon production and correlations in pp and p-Pb collisions at LHC with ALICE

Isolated photon production in pp collisions is one of the most clear tests of hard QCD processes and proton structure functions. Their measurement in pA collisions provides the possiblity to check initial geometrical scaling and possible modifications of the nucleon structure function in nuclei. Furthermore, the isolated photons constrain the kinematics of scattered partons and therefore, the measurement of isolated photon-hadron correlations has some advantages in the extraction of parton fragmentation function in pp and pA collisions.
ALICE collected data on pp and p-Pb collisions at several colliding energies. Thanks to the low material budget, ALICE is able to measure isolated photons down to relatively small $p_{\rm T} \sim 10$ GeV/$c$, thus probing structure functions down to small $x$. In this talk, the isolated photon spectra measured in pp collisions at $\sqrt{s}$ = 5.02 and 7 TeV will be presented and compared to those in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. By constructing the nuclear modification factor even stronger constraints on the geometrical model and the amount of modification of nucleon structure functions in nuclei can be provided due to partial error cancelation. Additionally, the isolated photon-hadron correlations in pp and p-Pb collisions will be presented and contrasted with the corresponding fragmentation functions and jet-hadron correlations at the LHC.

Speaker: Dhruv Utpalkumar Dixit (Lawrence Berkeley National Lab. (US))

isolatedphotonsHardProbes2020_Final.pdf

Recording

Parallel: A3 - Heavy Flavor I

Convener: Magdalena Djordjevic (Institute of Physics Belgrade)

27 Heavy Flavor Kinematic Correlations in Cold Nuclear Matter

It has been proposed that the azimuthal distributions of heavy flavor quark-antiquark pairs may be modified in the medium of a heavy-ion collision. This assumption was tested through next-to-leading order (NLO) calculations of the azimuthal distribution, $d\sigma/d\phi$, including transverse momentum broadening, employing $\langle k_T^2 \rangle$ and fragmentation in exclusive $Q \overline Q$ pair production [1].

The results have been compared to $p+p$ and $p + \overline p$ data on $Q \overline Q$ azimuthal correlations [1] as well as $b \overline b$ mass, pair $p_T$, rapidity, rapidity gap, $p_T$ asymmetry and azimuthal difference correlations in $p+p$ collisions through their decays to $J/\psi J/\psi$, as measured by LHCb [2]. Agreement with the data was found to be excellent.

Possible cold and hot matter effects on these correlations are investigated through the effects of nuclear modifications of the parton densities, enhanced $k_T$ broadening and energy loss.

[1] R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907.

[2] R. Vogt, arXiv:1908.05320 [hep-ph], submitted to Phys. Rev. C.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics (Nuclear Theory) under contract number DE-SC-0004014.

Speaker: Ramona Vogt (LLNL)

hp20_talk.pdf

Recording

28 Probing QCD medium effects in pPb collisions via the multiplicity dependence of J/$\psi$ and $\psi$(2S) production with the CMS experiment

Evidence for collectivity and effects beyond nPDF modifications and energy loss in small systems has been observed in recent years. In high-multiplicity pPb events, J/$\psi$ is found to show a surprisingly large long-range elliptic anisotropy signal, comparable to that for light and open-heavy flavor hadrons. In addition, results on prompt J/$\psi$ and $\psi(2S)$ production in pPb data at 5.02 TeV exhibit a different modification of the ground and excited state, especially in the Pb-going direction, hinting to a possible breakup of the weaker bound excited states from interactions with final state particles. To better understand the production mechanism of charmonia in small systems as well as the importance of final-state effects, the multiplicity dependence of J/$\psi$ and $\psi(2S)$ production yields and forward-backward asymmetries in pPb collisions at 8.16 TeV using full LHC run 2 statistics have been studied, and the results will be presented in this talk.

Speaker: Yousen Zhang (Rice University (US))

HardProbe2020_yousen_v5.pdf

Recording

29 Open heavy-flavour production from small to large collision systems with ALICE at the LHC

Heavy flavours are effective probes of the hot and dense matter, the Quark-Gluon plasma (QGP), produced in ultra-relativistic heavy-ion collisions. Due to the very short time scale characterising their production, they experience the whole evolution of the system. In particular, measurements of heavy-flavour production in Pb-Pb collisions at the LHC energies, including nuclear modification factors, give insight on the mechanisms of heavy-quark transport and energy loss in the hot and dense QCD matter.

In small hadronic systems like pp and p-Pb, heavy-flavour production provides the baseline for observations of hot-medium effects in heavy-ion collisions, as well as tests of perturbative QCD and measurements of cold-matter effects in the nuclear medium. On top of that, heavy-flavour measurements in small systems recently gained additional interest due to the possibility of observing specific initial- and final-state effects affecting the production mechanisms, driven by the particle multiplicity acting as an effective scaling parameter.

In this contribution, ALICE results on open heavy-flavour production in pp, p-Pb and Pb-Pb collisions at various energies will be discussed. New measurements will be presented both for fully-reconstructed charmed mesons and for single electrons and single muons from heavy-flavour hadron decays.

Speaker: Fabio Catalano (Politecnico e INFN Torino (IT))

OpenHF_Catalano_HP2020_final.pdf

Recording

30 Open heavy flavor production in pA collisions

Within the two p-Pb data samples collected by the LHCb detector at sqrt(s_NN) = 5 and 8.16 TeV, a rich set of open charm hadrons is observed with abundant statistics. Thanks to the LHCb forward acceptance that is complementary to general purpose detectors, with excellent performances in particle reconstruction and identification, these charm states are studied down to zero pT with overwhelming precision. In this talk, we present measurements of charm mesons and baryons productions, reconstructed in exclusive hadronic final states. Beauty hadrons, with signal counts up to a few thousands in the fully reconstructed decays in the pPb data samples, are also shown. Comparisons between theory predictions and data regarding the nuclear modification factors, forward-to-backward production ratios and baryon-to-meson ratios are made. The impact of the results, in particular on the improvement of nuclear PDF and parton saturation, are discussed. The open charm production in fixed-target collisions of LHCb is also presented, which provides crucial constraints on intrinsic charm and nuclear parton distribution functions at moderate and large Bjorken x.

Speaker: Jianqiao Wang (Tsinghua University (CN))

OpenHF_HP.pdf

Recording

31 Cold Nuclear Matter Effects on J/$\psi$ and $\Upsilon$ Productions at RHIC with the STAR Experiment

Quarkonia are excellent probes for studying the properties of quark-gluon plasma formed in relativistic heavy-ion collisions at RHIC. In order to fully understand the observed suppression of quarkonium production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV, it is essential to understand well the cold nuclear matter (CNM) effects on the quarkonium production. Collisions of p+Au at the same energy can be used to study the CNM effects since these effects are expected to be dominant in such systems.

In this talk, we will present measurements of inclusive J/$\psi$ and $\Upsilon$ cross-sections in p+p collisions and their modification in p+Au collisions (the nuclear modification factor $R_{pAu}$) at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV. The results are extracted from data recorded by the STAR experiment in 2015 using the di-electron decay channel of the quarkonia. Comparisons are made to results from other experiments as well as to model calculations and physics implications will also be discussed.

Speaker: Ziyue Zhang (University of Illinois at Chicago)

hp2020_slides_zyzhang_quarkonia_run15.pdf

Recording

Parallel: A4 - Initial State I

Convener: Kari J. Eskola (University of Jyvaskyla)

32 Evidence for top quark production in nucleus-nucleus collisions with the CMS experiment

Evidence for the production of top quarks in heavy ion collisions is reported in a data sample of lead-lead collisions recorded in 2018 by the CMS experiment at a nucleon-nucleon center-of-mass energy of $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = 5.02$ TeV, corresponding to an integrated luminosity of $1.7\pm0.1\,\text{nb}^{-1}$. Top quark pair ($\mathrm{t\bar{t}}$) production is measured in events with two opposite-sign high-$p_{\mathrm{T}}$ isolated leptons ($\ell^\pm\ell^\mp =\,\mathrm{e}^{+} \mathrm{e}^{-},\,\mu^{+} \mu^{-},\,\text{and}\,\mathrm{e}^{\pm} \mu^{\mp}$). We test the sensitivity to the $\mathrm{t\bar{t}}$ signal process by requiring or not the additional presence of b-tagged jets, and hence the feasilibilty to identify top quark decay products irrespective of interacting with the medium (bottom quarks) or not (leptonically decaying W bosons). To that end, the inclusive cross section ($\sigma_\mathrm{t\bar{t}}$) is derived from likelihood fits to a multivariate discriminator, which includes different leptonic kinematic variables, with and without the b-tagged jet multiplicity information. The observed (expected) significance of the $\mathrm{t\bar{t}}$ signal against the background-only hypothesis is 4.0 (6.0) and 3.8 (4.8) standard deviations, respectively, for the fits with and without the b-jet multiplicity input. After event reconstruction and background subtraction, the extracted cross sections are $\sigma_\mathrm{t\bar{t}} = 2.02 \pm 0.69$ and $2.56\pm 0.82\,\mu\mathrm{b}$, respectively, which are consistent with each other and lower than, but still compatible with, the expectations from scaled proton-proton data as well as from perturbative quantum chromodynamics predictions. This measurement constitutes the first step towards using the top quark as a novel tool for probing strongly interacting matter.

Speaker: Dr Georgios Krintiras (The University of Kansas (US))

CMS PAS HIN-19-001

HP2020_GKKrintiras.pdf

Recording

33 Photoproduction of $J/\psi$-mesons off deuteron in d+Au Ultra-Peripheral Collisions using the STAR detector

Nuclear dynamics at short distances among nucleons is one of the most outstanding phenomena in nuclear physics. Understanding the role of QCD in generating nuclear forces is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs have been observed from light to heavy nuclei using fixed target experiments at Jefferson lab via high energy electron-nucleus scattering. It has been recently suggested that the exclusive $J/\psi$ production of electron-deuteron scattering at the Electron-Ion Collider (EIC) would provide new insights into the SRCs, in particular from the aspect of the underlying quark-gluon dynamics. In the absence of electron-nucleus data from an EIC, data from deuteron-gold (d+Au) ultra-peripheral collisions (UPCs) recorded by the STAR detector at the Relativistic Heavy Ion Collider can be used as a proxy to test various techniques and hypotheses. The coherent and incoherent cross sections of $J/\psi$ photoproduction in d+Au UPC events are measured, and the implications of the results will be discussed. The reported results will be a first-time measurement of $J/\psi$-meson photoproduction off deuteron in high energy collisions.

Speaker: Zhoudunming Tu (BNL)

Recording

slides_deuteron_Kong-v3.pdf

34 Dipole model at Next-to-Leading Order meets HERA data

Deep inelastic scattering (DIS) total cross section data at small-x as measured by the HERA experiments is well described by Balitsky-Kovchegov (BK) evolution in the leading order dipole picture [1-3]. Recently the full Next-to-Leading Order (NLO) dipole picture total cross sections have become available for DIS [4-6], and a working factorization scheme has been deviced which substracts the soft gluon divergence present at NLO [7].
We report our ongoing work in which we make the first comparisons of the NLO DIS total cross sections to HERA data. The non-perturbative initial condition to BK evolution is fixed by fitting the HERA reduced cross section data. As the NLO results for the DIS total cross section are currently available only in the massless quark limit, we also fit a light quark only cross section constructed with a parametrization of published total and heavy quark data. We find an excellent description of the HERA data. Since the full NLO BK equation is computationally expensive [8], we use a number of beyond LO prescriptions for the evolution that include most important higher order corrections enhanced by large transverse logarithms, including the recent version of the equation formulated in terms of the target rapidity [9].

[1] T. Lappi, H. Mäntysaari, Phys.Rev. D88 (2013) 114020
[2] E. Iancu, J.D. Madrigal, A.H. Mueller, G. Soyez, D.N. Triantafyllopoulos, Phys.Lett. B750 (2015) 643-652
[3] B. Ducloué, E. Iancu, G. Soyez, D.N. Triantafyllopoulos, arXiv:1912.09196 [hep-ph]
[4] G. Beuf, Phys.Rev. D94 (2016) no.5, 054016
[5] G. Beuf, Phys.Rev. D96 (2017) no.7, 074033
[6] H. Hänninen, T. Lappi, R. Paatelainen, arXiv:1711.08207 [hep-ph]
[7] B. Ducloué, H. Hänninen, T. Lappi, Y. Zhu, Phys.Rev. D96 (2017) no.9, 094017
[8] T. Lappi, H. Mäntysaari, Phys.Rev. D91 (2015) no.7, 074016
[9] B. Ducloué, E. Iancu, A.H. Mueller, G. Soyez, D.N. Triantafyllopoulos, JHEP 1904 (2019) 081

Speaker: Henri Hänninen (University of Jyväskylä)

hänninen_nlodis_hp2020.pdf

Recording

35 Finite Nc corrections in the Balitsky-Kovchegov equation at next-to-leading order

The Colour Glass Condensate effective field theory is a useful framework for studying heavy ion collisions at ultrarelativistic energies, such as those reached at the Large Hadron Collider at CERN. In this framework, we study the rapidity evolution of Wilson lines that appear explicitly in cross section expressions. The next-to-leading order BK (Balitsky-Kovchegov) equation for the 2-point Wilson line correlator involves 6-point correlators of Wilson lines. These correlators are typically calculated only in the large-Nc limit. I will present a fully analytic calculation of these correlators in the finite Nc case, using the Gaussian Truncation. We use these results to find the relative importance of finite Nc corrections to the next-to-leading order evolution equation. We show numerically that the finite Nc corrections are negligible, as expected.

Speaker: Andrecia Ramnath (University of Jyvaskyla)

HP_final_Ramnath.pdf

Recording

36 Measurements of $v_n$ at high-$p_{\mathrm{T}}$ and correlation between $v_n$ and mean-$p_{\mathrm{T}}$ in $p$+Pb collisions with the ATLAS detector

This talk presents ATLAS measurements of the azimuthal anisotropy for charged particles in 8.16 TeV $p$+Pb collisions up to a $p_T$ of 50 GeV. The measurements are performed via the two-particle correlation method and the statistics are enhanced at high-$p_T$ by selecting events triggered by a high-$p_T$ jet. Restrictions on other particles are imposed to suppress the contribution from jets. Measurements of the resulting second- and third-order flow coefficients are presented in intervals of $p$+Pb event activity classes. The results from jet-triggered events are compared to those from minimum-bias $p$+Pb events, and the differences between the two event samples are analyzed in terms of the different origin of particles in these events, such as the different fraction of particles that arise from the jet fragmentation process.
In A+A collisions non-zero flow coefficients at high-$p_{T}$ are understood to arise from the path-length dependent energy loss of jets. Thus, these measurements in $p$+Pb collisions, can provide information on the origin of these collective phenomena.
To further assess properties of the azimuthal anisotropy in $p$+Pb collisions, the correlation between the mean transverse momentum and the magnitudes of the flow harmonics is also measured. The measurements are performed in 5.02 TeV $p$+Pb collisions for several intervals of the charge particle transverse momentum and as a function of the event-multiplicity. The measured correlations are compared to similar measurements in Pb+Pb collisions.

Speaker: Tomasz Bold (AGH Univ. of Science and Technology, Krakow)

2020-06-HP-bold-flow.pdf

Recording

12:40 Coffee break

Parallel: B1 - Jets and High-PT Hadrons II

P2

Convener: Peter Martin Jacobs (Lawrence Berkeley National Lab. (US))

37 Jet quenching and acoplanarity via hadron+jet measurements in pp and Pb-Pb collisions at 5.02 TeV with ALICE

We present the semi-inclusive distribution of charged jets recoiling from a trigger hadron in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. This technique provides a precise data-driven subtraction of the large uncorrelated background contaminating the measurement. It uniquely enables the exploration of medium-induced modification of jet production and acoplanarity over a wide phase space, including the low jet $p_\mathrm{T}$ region for large jet resolution parameter $R$. Medium-induced jet deflection may occur via multiple soft scatterings resulting in a broadening of the overall azimuthal correlation between the trigger hadron and the recoiling jet. In addition, the tail of this azimuthal correlation is sensitive to Molière scatterings off quasi-particles in the medium. A search for these phenemona in Run 1 data using hadron-jet acoplanarity showed no evidence of large-angle jet broadening with respect to the vacuum expectation within experimental uncertainties. However, recent theoretical work has highlighted that low hadron trigger $p_\mathrm{T}$ and low recoiling jet $p_\mathrm{T}$ configurations show more sensitivity to in-medium modifications to the acoplanarity.

This talk will report measurements of medium-induced jet energy redistribution through the comparison of trigger-normalized recoil jet yields in different centrality intervals for Pb-Pb collisions and in minimum-bias pp collisions, and of jets with different $R$. We also present a new measurement of hadron-jet acoplanarity in pp and Pb-Pb collisions using high-statistics Run 2 data, with emphasis on the region of low recoil jet $p_\mathrm{T}$.

Speaker: Jaime Norman (University of Liverpool (GB))

HardProbes2020_v4.pdf

Recording

38 Effects of in-medium k_T broadening on di-jet observables

---

Heavy ion collisions at high energies can be used as an interesting way to recreate and study the medium of the quark-gluon plasma (QGP). We particularly investigate the jets produced in hard binary collisions and their interactions with a tentative medium. These jets were obtained numerically from the Monte-Carlo simulations of hard collisions using the KATIE-framework [1], where parton momenta within the colliding nucleons were describe by means of transverse momentum distributions (TMD). We evolved these jets within a medium that contains both, transverse kicks (yielding a broadening in momentum transvers to the jet-axis) as well as medium induced radiation within the MINCAS-framework [2] following the works of [3,4]. After favorable comparison of our results with experimental LHC-data on jet-quenching we make predictions for the decorrelation of dijets. In particular, we study deviations from a transverse momentum broadening that follows a Gaussian distribution. References: [1] A. van Hameren, Comput.Phys.Commun. 224 (2018) 371-380 [2] K. Kutak, W. Płaczek, R. Straka, Eur.Phys.J. C79 (2019) no.4, 317 [3] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1301 (2013) 143 [4] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1406 (2014) 075

Speaker: Martin Rohrmoser (IFJ-PAN Krakow)

hardprobes2020_rohrmoser.pdf

Recording

39 Jet quenching and scaling properties of medium-evolved gluon cascade in expanding media

We present a study of the impact of the expansion of deconfined medium on single-gluon emission spectra and the jet suppression factor ($Q_{AA}$) within the BDMPS-Z formalism. These quantities are calculated for three types of media (static medium, exponentially decaying medium and Bjorken expanding medium). The distribution of medium-induced gluons and the jet $Q_{AA}$ are calculated using the evaluation of in-medium evolution with splitting kernels derived from the gluon emission spectra. A universal behavior of splitting kernels is derived for low-$x$ and high-$x$ regimes in the asymptote of large times and its impact on the resulting jet $Q_{AA}$ is discussed. For the full phase-space of the radiation, the scaling of jet $Q_{AA}$ with an effective quenching parameter is derived. The importance of the medium expansion for precise modeling of jet quenching phenomena as well as steps towards generalizing the results to other jet quenching observables are discussed.

Speaker: Dr Souvik Priyam Adhya (Institute of Particle and Nuclear Physics Faculty of Mathematics and Physics, Charles University)

hp2020_souvik.pdf

Recording

40 Simple implementation of color coherence for the resumation of soft BDMPS-Z gluons

The evolution of QCD jets under the influence of a dense colored medium leads to the non trivial modification of the emission spectrum. In the multiple soft scattering regime, for sufficiently large mediums, soft and wide angle emissions can be resummed, at large number of colors, since the emissions become independent up to $\tau_{br}/L$ corrections. Similarly to DGLAP evolution, such cascades correspond to pure Markovian processes and therefore interferences between partons are neglected. This constraint means that color coherence effects are absent. In the vacuum this coherence effect is critical to guarantee that the shower is angular ordered.
In this talk, we present a simple procedure to implement into the rate equations corrections coming from the color (de)coherence of the medium cascade. The final equation we obtain is remarkably simple and open to direct physical interpretation.

Speaker: João Barata (BNL and University of Santiago de Compostela/IGFAE)

HP20_Barata.pdf

Recording

Parallel: B2 - Heavy Flavor II

Convener: Marcelo Gameiro Munhoz (Universidade de Sao Paulo (BR))

41 Transport coefficients from in medium quarkonium dynamics

Three are the mechanisms that influence quarkonium suppression in a medium: screening, thermal decay, and recombination. In recent years, a framework that can treat them consistently at the same time has been put forward, the open quantum system approach. In this talk, we will discuss how the combination of open quantum system and Effective Field Theory techniques are useful to understand quarkonium evolution in a medium in the regime in which the temperature is smaller than the inverse of the typical radius. In this case, the interaction parameter depends only on two transport coefficients $\kappa$ and $\gamma$, where $\kappa$ is the heavy quark diffusion coefficient. Combining these results with recent lattice QCD evaluations of the mass shift and thermal decay width of quarkonium we are able to obtain a non-perturbative determination of $\kappa$ compatible with state-of-the-art results. This talk is based on the recent paper Phys.Rev. D100 (2019) no.5, 054025.

Speaker: Miguel Ángel Escobedo Espinosa (Instituto Galego de Física de Altas Enerxías)

escobedo_hp2020.pdf

Recording

42 Quarkonium production in Pb+Pb collisions with ATLAS

The yields of bound quarkonium states in heavy-ion collisions provide a powerful tool to probe the dynamics of the hot, dense plasma. These measurements are sensitive to the effects of color screening, color recombination, and possibly to other, new phenomena affecting dynamics of heavy quarks in the QCD medium. In this talk, the ATLAS results on bottomonium nuclear modification factor and excited-to-ground state ratio using 2018 Pb+Pb data and 2017 $pp$ data both at 5.02 TeV will be presented as a function of transverse momentum and event centrality.

Speaker: Songkyo Lee (Iowa State University (US))

20200601_songkyo_HP2020_v3.pdf

Recording

43 Nuclear modification factor and flow measurements of quarkonia in p-Pb and Pb-Pb collisions with ALICE at LHC

Heavy quarks are produced in the earliest stages of a nucleus-nucleus collision and therefore are an important tool to study the subsequent high energy-density medium formed in relativistic heavy-ion collisions. Over the last few decades major efforts have been undertaken in order to understand the properties of the quark-gluon plasma (QGP) using quarkonia. The extent of medium modification for heavy-quark production in heavy-ion collisions is measured in terms of the nuclear modification factor $R_{\rm AA}$. However, modifications of quarkonium production may also occur due to cold nuclear matter (CNM) effects such as shadowing of nuclear parton distribution function, gluon saturation and others. In recent data, strong suppression patterns have been seen in $\Upsilon$ $R_{\rm AA}$ whereas a recombination of individual charm quarks as dominant production mechanism for charmonium states, in particular J/$\psi$ for low transverse momentum and most central collisions. These individual charm quarks are expected to be (at least partially) equilibrated and together with initial anisotropies from the collision geometry result in a positive J/$psi$ elliptic flow. At higher transverse momentum, the J/$\psi$ elliptic flow in high-multiplicity p-Pb collisions shows values similar to those from Pb-Pb collisions, suggesting a common production mechanism in this kinematic region.

ALICE J/$\psi$ and $\Upsilon$ $R_{\rm AA}$ results for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented as a function of centrality, $p_{\rm T}$ and rapidity. The inclusive as well as prompt and non-prompt J/$\psi$ production will be discussed for the $R_{\rm AA}$ measurement at mid-rapidity for p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The CNM effects will be also explored for the $\Upsilon$ and $\psi({\rm 2S})$ in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. The $p_{\rm T}$-differential inclusive J/$\psi$ elliptic flow at mid-rapidity ($|y|<0.9$) will be shown together with the J/$\psi$ elliptic and triangular flow at forward rapidity ($2.5 < y < 4$) in Pb-Pb collisions. These results will be compared to $\Upsilon(1S)$ elliptic flow in Pb-Pb collisions. In addition, measurements of J/$\psi$ elliptic flow in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and 8.16 TeV will be presented at forward ($2.03 < y < 3.53$) and backward ($-4.46 < y < -2.96$) rapidity.
Finally, the ALICE results will be compared with those obtained by other LHC experiments and the current theoretical interpretation of the results will be also discussed.

Speaker: Florian Damas (Centre National de la Recherche Scientifique (FR))

quarkoniaHP2020_final.pdf

Recording

44 Coupled Transport Equations for Quarkonium Production in Heavy Ion Collisions

The production of heavy quarkonium in heavy ion collisions has been used as an important probe of the quark-gluon plasma. To describe the in-medium evolution of quarkonium, one has to take into account plasma screening effects and recombination in a consistent way. Many previous studies calculate dissociation rates from QCD but use recombination models that are based on detailed balance or coalescence. Thus the implementations of dissociation and recombination are not in the same theoretical framework.

Motivated by the recent developments in applying open quantum system to study quarkonium in-medium dynamics, we construct a set of coupled transport equations of open heavy quarks and quarkonia. In our framework, both dissociation and recombination rates are calculated from QCD. The recombination process depends on real-time distributions of open heavy quarks. An important feature of our implementation of recombination is the cross-talk recombination: an excited quarkonium state that dissociates early in the evolution when the plasma is hot may recombine into the ground state shortly after the dissociation and vice versa when the temperature drops. In this talk, we will show new phenomenological results on Upsilon production based on our coupled transport equations approach, with an improved treatment of feed-down contributions in the hadronic stage. We will also discuss the importance of the cross-talk recombination in phenomenology.

Speaker: Xiaojun Yao (Massachusetts Institute of Technology)

hard_probe_XY.pdf

Recording

Parallel: B3 - Heavy Flavor III

Convener: Lijuan Ruan

45 Flavor hierarchy of jet quenching in relativistic heavy-ion collisions

Relativistic heavy-ion experiments have observed similar quenching effects for (prompt) $D$ mesons compared to charged hadrons for transverse momenta larger than 6-8 GeV, which remains a mystery since heavy quarks typically lose less energies in quark-gluon plasma than light quarks and gluons. Recent measurements of the nuclear modification factors of $B$ mesons and $B$-decayed $D$ mesons by the CMS Collaboration provide a unique opportunity to study the flavor hierarchy of jet quenching. Using a linear Boltzmann transport model combined with hydrodynamics simulation, we study the energy loss and nuclear modification for heavy and light flavor jets in high-energy nuclear collisions. By consistently taking into account both quark and gluon contributions to light and heavy flavor hadron productions within a next-to-leading order perturbative QCD framework, we obtain, for the first time, a satisfactory description of the experimental data on the nuclear modification factors for charged hadrons, $D$ mesons, $B$ mesons and $B$-decayed $D$ mesons simultaneously over a wide range of transverse momenta (8-300 GeV). This presents a solid solution to the flavor puzzle of jet quenching and constitutes a significant step towards the precision study of jet-medium interaction. Our study predicts that at transverse momenta larger than 30-40 GeV, $B$ mesons also exhibit similar suppression effects to charged hadrons and $D$ mesons, which may be tested by future measurements.

Reference:

[1] Wen-Jing Xing, Shanshan Cao, Guang-You Qin, and Hongxi Xing, arXiv:1906.00413

Speaker: Ms Wen-Jing Xing (Central China Normal University)

Recording

WJX_HP2020_final.pdf

46 A study of open-heavy-flavor, heavy-jet, and correlations using the LIDO transport model

Understanding heavy-flavor transport properties and energy loss inside a quark-gluon plasma (QGP) is a major interest of the heavy-ion phenomenology. In this work, we combine both open-heavy and heavy-flavor jet observables to study the average heavy quark energy loss as well as its fluctuations. Low-momentum heavy quark interacts with QGP mainly through elastic collisions; for high-momentum heavy quark, elastic collisions also induce radiative energy loss. Both energy loss mechanisms can be related to the heavy-quark momentum diffusion coefficient ($\hat{q}$). Recently, we have extracted a temperature and momentum-dependent $\hat{q}$ by comparing to open-heavy-flavor observables ($R_{AA}$ and $v_2$) using the LIDO transport model [1,2]. We find that even after the parameter calibration, the model still has a large degree of freedom to switch between a Boltzmann equation with large-angle perturbative scattering and a diffusion equation with effective transport coefficients. The reason is that inclusive open-heavy flavor observables are more sensitive to the average energy loss, but they are less efficient in discriminating models with different energy-loss fluctuations (e.g. large-angle scattering and diffusion). We argue that the fluctuation information can be studied using the heavy-flavor jet. First, we use the calibrated model to predict the charmed- and bottom-jet nuclear modification factor. Then, we study traces of the heavy-quark energy-loss fluctuations encoded in the angular and transverse momentum correlations between heavy flavor particles and jets. These observables help to understand heavy-quark-medium interaction in greater detail.

[1] W. Ke, Y. Xu, and S. A. Bass, Phys. Rev. C 98, 064901 (2018).
[2] W. Ke, Y. Xu, and S. A. Bass, Phys. Rev. C 100, 064911 (2019).

Speaker: Dr Weiyao Ke (University of California, Berkeley)

Recording

WeiyaoKe-HP20-HF.pdf

47 New PHENIX Results on Mid-Rapidity Bottom and Charm Production in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV

Energy loss of quarks in the hot and dense medium has been studied for
decades. Both the experimental and theoretical efforts hinted that the
energy loss is quark mass dependent (the yield of heavier quarks will be
less suppressed). It was found that the electrons from heavy quarks (charm,
and bottom) are less or similarly suppressed compared to that of light
hadrons. The mass ordering of the suppression between charm and bottom was
not clear by now due to large experimental uncertainties. We have fully
exploited the events recorded at PHENIX from Au+Au collisions from RHIC
Year-2014 run, and with the new charm and bottom $p_{T}$ spectra from p+p
collisions from Year-2015 run, we can obtain the new $R_{AA}$ for charm and
bottom quarks with smaller uncertainties. We will show the latest results on
the $R_{AA}$ of electrons and unfolded hadrons from charm and bottom quarks
separately, and implications on the understanding of the quark mass
dependence of the energy loss.

Speaker: Dr Ajeeta Khatiwada (Purdue University (US))

HardProbesAjeetaKhatiwada.pdf

Recording

48 Measurement of D$^\pm$ meson production in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV with the STAR experiment

Charm quarks are an excellent probe of the quark-gluon plasma created in heavy-ion collisions as they are produced at very early stages of such collisions and subsequently experience the whole evolution of the system. At STAR experiment, charm quark production can be accessed by direct topological reconstruction of open-charm hadrons thanks to an excellent track pointing resolution provided by the Heavy Flavor Tracker.

In this talk, we will present a measurement of D$^\pm$ meson production in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV by STAR using data collected in 2014 and 2016. Supervised machine-learning techniques were used to optimize the yield extraction from the three body hadronic decay channel $\textrm{D}^\pm \rightarrow \textrm{K}^\mp \pi^\pm \pi^\pm$. The D$^\pm$ invariant spectra were then obtained in 0-10\%, 10-40\%, and 40-80\% central Au+Au collisions. The measured nuclear modification factor $R_\mathrm{AA}$ as a function of transverse momentum $(p_\mathrm{T})$ reveals a significant suppression of high-$p_\mathrm{T}$ D$^\pm$ mesons in central and mid-central Au+Au collisions with respect to p+p collisions. The $(\textrm{D}^++\textrm{D}^-)/(\textrm{D}^0+\overline{\textrm{D}^0})$ yield ratio has also been extracted and compared to that from PYTHIA calculations.

Speaker: Jan Vaněk (Nuclear Physics Institute, Czech Academy of Sciences)

HP2020_Vanek_final.pdf

Recording

Parallel: B4 - Initial State II

Convener: Jamal Jalilian-Marian (Baruch College)

49 Angular de-correlation of forward di-hadrons: on the optimal $p_t$ range to probe gluon saturation

An important phenomenological consequence of the phenomenon of gluon saturation is the suppression of back-to-back hadron and jet pairs produced in the forward region of pA collisions. We present a new calculation of this process within the dilute-dense formalism of the color glass condensate (CGC) effective theory. Following Ref. [1], we collide a large-$x$, dilute probe, described in terms of parton distribution functions, off a dense target, described in terms of transverse momentum dependent (TMD) gluon distributions, whose small-x evolution we calculate using rcBK evolution. We then couple this cross section with the formalism introduced in Ref. [2] to implement in an analytically-controlled way the radiation of soft gluons (Sudakov resummation) from the initial and the final state.

We first apply this CGC+Sudakov framework to the production of forward di-jets at high-$p_t$ in pp and pA collisions. We use the same kinematic cuts and collision energy as in a recent analysis by the ATLAS collaboration [3]. We find that the suppression of the di-jet yield at $\Delta\phi=\pi$, predicted by gluon saturation, is essentially washed out by a strong effect of broadening induced by the radiation of soft gluons. Compatibly with ATLAS data, we find that the nuclear modification factor for forward high-$p_t$ dijets is at best of order $R_{pA}\approx 0.9$.

Motivated by this result, we propose to study the production of forward dihadrons (pions) at lower, though moderate, $p_t$ ($\approx 10$ GeV). We find that, in this case, the suppression of back-to-back pairs genuinely predicted by gluon saturation survives the broadening due to the Sudakov resummation. We indeed obtain $R_{pA} \approx 0.75$ at $\Delta\phi=\pi$ using kinematic cuts compatible with the proposed FoCal upgrade of the ALICE detector. We conclude that forward dihadrons at high $p_t$ provide a sensitive probe of gluon saturation at LHC.

[1] J. L. Albacete, G. Giacalone, C. Marquet and M. Matas, https://arxiv.org/abs/1805.05711
[2] A. Stasto, S-Y. Wei, B-W. Xiao, and F. Yuan https://arxiv.org/abs/1805.05712
[3] ATLAS Collaboration https://arxiv.org/abs/1901.10440

Speaker: Shu-yi Wei (ECT*)

dihadron.pdf

Recording

50 Forward quark jet-nucleus scattering in a light-front Hamiltonian approach

We investigate the scattering of a quark jet on a high-energy heavy nucleus using the time-dependent light-front Hamiltonian approach. We present the real-time evolution of the quark-jet in a strong classical color field of the incoming nucleus described by the Color Glass Condensate effective theory. We calculate the cross section, the differential cross section, and the quark jet distribution function in coordinate space as well as in color space. We study the sub-eikonal effect by letting the quark jet carry realistic finite longitudinal momenta, and we find sizeable changes on the transverse coordinate distribution of the quark. We then extend our investigation by including dynamical gluons and study jet quenching with gluon emissions.

Speaker: Meijian Li (University of Jyväskylä)

HP2020_MeijianLi.pdf

Recording

51 Study of in-medium momentum broadening with photon-jet momentum correlations in PbPb collisions at 5.02 TeV in the CMS experiment

Studies of jet energy loss and momentum broadening with photon-jet momentum and angular correlations will be presented, with PbPb data at 5.02 TeV collected by the CMS detector. Photon-jet events provide a means of probing in-medium jet energy loss with good constraints on the initial parton kinematics and flavor. Studies of momentum and angular correlations in photon-jet events can enable precision measurements of jet quenching effects, such as energy loss and momentum broadening, which are important towards a full understanding of the underlying mechanisms of jet quenching.

Speaker: Molly Taylor (Massachusetts Inst. of Technology (US))

Recording

Taylor_Molly_HP2020.pdf

52 Exploring potential jet modification in small collision systems with two particle correlations at PHENIX

Flow results in small systems at RHIC and the LHC indicate QGP droplets are
formed in these collision systems. Measurements of jet $R_{pA}$ on the other
hand are consistent with no modification to the jets produced.  However,
non-zero $v_n$ values for high momentum particles, which in A+A collisions
are attributed to path-length dependent energy loss, have been observed in
small systems. To further probe possible modification to jet particles,
PHENIX measures the relative modification of the near and away-side jet
particles in pi0-hadron correlations in 200 GeV d+Au and 3He+Au collisions.
Modifications similar to the high $p_T$ suppression and low momentum
enhancement of associated particles observed in A+A collisions have been
observed in d+Au collisions. These surprising results have now also been
seen in 3He+Au data. These PHENIX measurements and possible interpretations
of these intriguing results will be presented.

Speaker: Cheuk-Ping Wong

hardProbes2020.pdf

Recording

Tuesday 2 June

Poster session

53 $\it{R}_{\rm{AA}}$ of electrons from open beauty-hadron decays in Pb-Pb collisions at $\sqrt{\it{s}_{\rm{NN}}}$ = 5.02 TeV with ALICE

The LHC heavy-ion physics program aims at investigating the properties of strongly-interacting matter in extreme conditions of temperature and energy density, where the formation of the Quark-Gluon Plasma (QGP) is expected. Heavy quarks (charm and beauty) are regarded as unique probes of the properties of the QGP as they are created on a very short time scale in initial hard scattering processes, therefore, they witness the full evolution of the system. In particular, beauty quarks, being four times heavier than charm quarks, can be used to study the in-medium mass dependent energy loss.

Beauty production can be studied via semi-electronic decays of beauty hadrons. The yield of electrons coming from open beauty-hadron decays is obtained by fitting the impact parameter distribution with templates of different electron sources.

In this contribution, the measurements of electrons from beauty-hadron decays in Pb-Pb collisions at $\sqrt{\it{s}_{\rm{NN}}}$ = 5.02 TeV with the ALICE detector will be presented. For different centrality classes, the $\it{R}_{\rm{AA}}$ of beauty-hadron decay electrons is compared to that of electrons coming from charm and beauty hadron decays and with model calculations.

Speaker: Jonghan Park (Inha University (KR))

200602_HardProbe_poster.pdf

Zoom Meeting Link

54 $\Lambda_{c}$ production in pp collisions at $\sqrt{s}=13$ TeV with ALICE at the LHC

Charm quarks are a powerful probe of the Quark-Gluon Plasma (QGP) formed in high-energy heavy-ion collisions. Produced in hard scattering processes on a timescale shorter than the QGP formation time, they experience the whole evolution of the medium interacting with its constituents. The measurements of charm-hadron production allow testing the mechanisms of in-medium parton energy loss. Moreover, the study of charm-baryon production in heavy-ion collisions and, in particular, the baryon-to-meson ratio, provides unique information on hadronisation mechanisms, constraining the role of coalescence and testing the predicted presence of diquark states in the medium.
Measurements of charm-baryon production in pp and p–Pb collisions are essential to establish a baseline for Pb–Pb collisions. In particular, the $\Lambda_{c}/D_{0}$ ratio is expected to be enhanced with respect to the proton-proton baseline if charm quarks hadronise via recombination with the surrounding light quarks in the QGP. In this scenario, the presence of diquark bound states in the QGP could further increase the $\Lambda_{c}$ production. Thus, charm baryons are ideal tools to investigate unexplored aspects of the QGP. The ALICE detector is well suited to detect charm baryons down to low $p_{T}$ thanks to the excellent tracking, vertexing and particle identification capabilities.

In this poster, the new ALICE results about the $\Lambda_{c}$ in pp collisions at $\sqrt{s}=13$ TeV will be shown. The measurement of $\Lambda_{c}$ production at mid-rapidity ($|y|<0.5$) as a function of charged-particle multiplicity will be discussed.

Speaker: Luigi Dello Stritto (Universita e INFN, Salerno (IT))

Lc production in pp collisions at √s=13 TeV with ALICE at LHC

posterhp_ldellost.pdf

poster_ldellost.mp4

55 $\rm{f}_{0}$(980) resonance production in small collision systems with ALICE

Short-lived resonances are powerful probes to understand the hadronic phase in ultra-relativistic heavy-ion collisions, due to their lifetimes of $\sim$10 fm/c, comparable to the time span between chemical and kinetic freeze-out. The measurements of short-lived resonances in small collision systems provide the baseline for heavy-ion collision measurements as well as exploration of cold nuclear matter effects, which can be achieved by comparison between measurements in pp and p-Pb collisions. We present the multiplicity dependence of the production of $\rm{f}_{0}$(980) at mid-rapidity $(\mid\rm{y}\mid<0.5)$ in pp collisions at $\sqrt{s} =$ 13 TeV and p-Pb collisions at $\sqrt{s_{\rm{NN}}} =$ 5.02 TeV. The measurement has been performed with ALICE at the LHC and the particles have been reconstructed in the $\rm{f}_{0}(980) \rightarrow \pi^{+}\pi^{-}$ decay channel. The poster will include details on the signal extraction, transverse momentum spectra, particle yield and mean transverse momenta of $\rm{f}_{0}$(980). In addition, the particle yield ratios and nuclear modification factor, $R_{\rm{pPb}}$ will be presented to explore the internal structure of $\rm{f}_{0}$(980).

Speaker: Junlee Kim (Jeonbuk National University (KR))

2020HP.m4v

2020HP_v5.pdf

ZOOM

56 Background fluctuations in jet studies in heavy ion collisions

Jets produced in high energy heavy ion collisions are quenched by the production of the quark gluon plasma. Measurements of these jets are influenced by the methods used to suppress and subtract the large, fluctuating background and the assumptions inherent in these methods. We compare measurements of the background by the ALICE collaboration [1] to PYTHIA Angantyr simulations of Pb-Pb collisions and to a data-driven random background generator. Angantyr over-estimates the predictions for the standard deviations of the energy in random cones at an approximate level of 15%, indicating that fluctuations due to mini-jets and resonances are not negligible in Angantyr. We are able to describe the standard deviation of the energy in random cones in the background generator as a convolution of number and momentum fluctuations in agreement with the form predicted in the ALICE paper. The description works well for an azimuthally isotropic background but slightly underestimates the width of the correlations for a flow-modulated background. We derive the expected impact of flow on the background and compare to the data-driven background generator.

[1] The ALICE Collaboration, JHEP 2012(3):53, March 2012.

Speaker: Christine Nattrass (University of Tennessee (US))

BackgroundFluctuationsHPPoster.pdf

GMT20200520-135604_Christine-_1920x1080.mp4

Link to April Meeting talk on the same analysis

Link to paper

Zoom meeting link

57 Beam test results of the sPHENIX HCal prototype and Performance Characterization of Scintillator Tiles

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will quantify the properties of quark-gluon plasma created in relativistic heavy ions collisions with a focus on the measurements of jets and Upsilon states. A crucial component to the sPHENIX detector design for jet measurements is the hadronic calorimeter (HCal) which is located outside of the solenoid magnet and composed of alternating layers of tapered steel plates and scintillator tiles. sPHENIX has performed four tests of the HCal prototypes at Fermilab since 2015 and pre-production design of the EMCal and HCal in the η∼1 configuration was tested at the Fermilab Test Beam Facility as experiment T-1044 in the spring of 2018. We will present the results of 2018 HCal prototype beam test, the results of sPHENIX-like calorimeter system and corresponding GEANT4 simulations. The energy linearity and resolution of pions and electrons will also be presented.

Speaker: Uttam Acharya (Georgia State University)

Beam Test Results of sPHENIX HCal Prototype and Performance Characterization of Scintillator Tiles

HP2020 _Poster_Audio.mov

HP2020_Poster.pdf

58 Charged-particle production as function of event multiplicity in ALICE

The ALICE experiment at the LHC is designed to investigate the properties of the Quark-Gluon Plasma by studying high-energy A--A collisions. Medium effects like parton energy loss can be examined by measuring the production of charged particles at high transverse momentum ($\textit{p}_{\text{T}}$). In particular, the correlation between $\textit{p}_{\text{T}}$ spectra and event multiplicity of charged particles can give a handle on the different production mechanisms of charged particles.
In this poster, we report on charged-particle $\textit{p}_{\text{T}}$ spectra as a function of the event multiplicity in pp collisions at $\sqrt{s} =$ 2.76, 5.02, 7 and 13 TeV as well as in p-Pb and Pb--Pb collisions at $\sqrt{s_{\text{NN}}} = $ 5.02 TeV to study the energy and system size dependence. By comparing to QCD-inspired models, this measurement can help in understanding the event multiplicity dependence of charged-particle production mechanism.

Speaker: Patrick Huhn (Johann-Wolfgang-Goethe Univ. (DE))

phuhn_mkrueger_HP_charged_particles.pdf

zoom meeting for poster session

59 Cold QCD with sPHENIX

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will enable a spectrum of new or improved cold QCD measurements, enhancing our understanding of the initial state for nuclear collisions. sPHENIX measurements in proton-proton and proton-nucleus collisions will reveal more about how partons behave in a nuclear environment, inform our understanding of the initial state in heavy-ion collisions, and provide comparative data to investigate modification of fragmentation functions.  Measurements will also take advantage of RHIC's unique capability to collide polarized protons on nuclei, which provides novel opportunities to study nuclear effects with spin observables.  A potential upgrade to sPHENIX with forward instrumentation could significantly enhance these physics capabilities. The cold QCD nuclear physics program for the proposed sPHENIX midrapidity detector as well as the enhanced program enabled with forward upgrades will be presented.

Speaker: Desmond Mzamo Shangase (University of Michigan (US))

Cold QCD with sPHENIX Final.pdf

Link to Poster Session 154 "Cold QCD with sPHENIX"

zoom_6.mp4

60 Constraining nPDFs with Drell-Yan production in pPb collisions with the CMS experiment

Nuclear parton distribution functions (nPDFs) of quarks and antiquarks affect the production of electroweak bosons in proton-lead (pPb) collisions. In this presentation, a new measurement of the Drell-Yan (DY) process is presented in pPb collision at the center of mass energy of 8.16 TeV with the CMS detector. The rapidity dependence of this process is particularly sensitive to nPDFs, but further information can be gained by studying the mass dependence of DY production, measured for the first time in pPb collisions at 8.16 TeV, down to 15 GeV. In addition, differential measurements in the dimuon $p_{\text{T}}$ or $\phi^{*}$ (an angular variable correlated with $p_{\text{T}}$ measured for the first time in pPb) provide insights on soft gluon emission at low $p_{\text{T}}$. Comparisons to theory calculations show that these data are sensitive to the presence of nuclear modifications to the parton distributions in the lead nucleus, and can help improve and constrain theoretical calculations.

Speaker: Émilien Chapon (Chinese Academy of Sciences (CN))

chapon_HP20.pdf

zoom_0.mp4

ZOOM link

61 D$^{*+}$ production in pp collisions at $\sqrt{s} = 13$ TeV with ALICE at the LHC

The ALICE experiment is devoted to study the Quark Gluon Plasma (QGP), which is the high-density state of matter, obtained in high-energy heavy-ion collisions, where quarks and gluons are deconfined. Since heavy quarks (charm, beauty) are created mostly with hard scatterings during the first stages of the collisions and their abundances remain constant while the system evolves, they can be used as effective and calibrated QGP probes.

Production of heavy quarks in pp collisions provides a stringent test to pQCD calculations and allows us to study multi-parton interactions by analyzing their production as a function of charged-particle multiplicity. In this poster, D$^{*+}$ (c$\overline{\mathrm{d}}$) production as a function of multiplicity in pp collisions at $\sqrt{s} = 13$ TeV using data recorded during 2016, 2017 and 2018 running periods will be presented.

Speaker: Marco Giacalone (Universita e INFN, Bologna (IT))

Poster HP2020.pdf

zoom_6.mp4

Zoom Meeting Room

62 D0-tagged jets in heavy-ion collisions with ALICE at the LHC

Charm quarks are ideal probes of the Quark-Gluon Plasma (QGP). Due to their large mass they are produced in the early stages of ultra-relativistic heavy-ion collisions in hard-scattering processes.

D$^{0}$-tagged jets are valuable tools to investigate the charm interaction with the QGP. Furthermore, charmed jets can provide information to study the mass-dependent energy loss by analysing the modification of their yield in Pb$-$Pb collisions with respect to pp collisions as a function of the jet transverse momentum.

D$^{0}$ mesons are reconstructed through their hadronic decay channels D$^{0} \to K\pi$. The large combinatorial background is rejected by applying topological selections exploiting the relatively large lifetime of D$^{0}$ mesons and the excellent particle-identification capabilities of the ALICE detector. The signal is extracted using an invariant mass analysis. Charged-track jets are reconstructed with anti-$k_{\rm T}$ algorithm. The ALICE detectors allow us to measure D$^{0}$-tagged jets down to low $p_{\rm T}$, where the probes are more sensitive to the effects of the hot medium. In this contribution, ALICE measurements of the production and fragmentation of D$^{0}$-tagged charged jets in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented.

Speaker: Antonio Carlos Oliveira Da Silva (University of Tennessee - Knoxville)

D0jetPbPb_HardProbes_poster.pdf

D0JetsInPbPb_ALICE_HP2020.mp4

Link to zoom room

63 DCA studies for separating prompt and non-prompt dielectrons in p–Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with ALICE

Dileptons are a prime probe of the deconfined state of strongly interacting matter, the Quark–Gluon Plasma (QGP), produced in high energy heavy ion collisions, as they are not affected by secondary strong interactions. A measurement of the thermal radiation from the QGP in the dielectron intermediate mass region allows to estimate the medium temperature. In this region the main component of the dielectron continuum is due to correlated semileptonic decays of B and D mesons. The proper decay length for B-mesons is $c\tau \approx$ 500 $\mu$m and for D mesons it is 100-300 $\mu$m, hence the reconstructed decay electrons do not point to the primary vertex of the collision.
Combining the measured distance of closest approach (DCA) of each single electron into a pair variable DCA$\rm _{ee}$ gives the possibility to separate prompt from non-prompt dielectron pairs or the charm and beauty contributions from each other. In small collisions systems this approach can be used to measure a possible modification of the heavy-flavour sources by cold nuclear matter effects, or to identify thermal radiation on top of the heavy-flavour contributions and with this serve as a reference for measurements in Pb–Pb collisions.
We will present most recent studies in p–Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.

Speaker: Horst Sebastian Scheid (Johann-Wolfgang-Goethe Univ. (DE))

Poster_Scheid_HP2020.pdf

Video_Scheid_HP2020.mp4

Zoom meeting

64 Direct Photon and π0 Identification in Au+Au Collisions at √sNN= 200 GeV in the STAR Experiment

Jets recoiling from a direct-photon have long been seen as a golden probe of the quark gluon plasma created in relativistic heavy ion collisions, due to the ability to tightly constrain the initial hard scattering kinematics. Until recently, the ability to measure this channel and the ensuing observables at RHIC were largely statistics-limited, owing to the small cross-section of direct photon production compared to, for example, the most abundant di-jet cross-section. In this poster, we will present methods for identifying direct photons and $\pi^0$, using the 13 nb$^{-1}$ of $\sqrt{s_{NN}} = 200$ GeV Au+Au data recorded in 2014 by the STAR experiment.

Speaker: Annika Ewigleben (Lehigh University)

Ewigleben_HP2020.pdf

Zoom Meeting Link ID#253, Annika Ewigleben

65 Direct photon measurements in pp collisions at sqrt(s)=510 GeV by PHENIX

At RHIC energies high pT direct photons are mainly produced by the
quark-gluon Compton scattering process. Being not disturbed by fragmentation
processes, they provide access to initial condition of partonic collisions.
Direct photon production in pp collisions serves an ideal probe for gluon
parton distribution functions (PDF), whereas quark PDFs are well constrained
by deeply inelastic lepton-nucleon scattering. Similarly, longitudinally
polarized pp collisions provide direct access to gluon helicity distribution
within the proton, and therefore contribute to resolving the long standing
puzzle of the proton spin decomposition. We will present the status of the
direct photon analysis from pp collisions at sqrt(s)=510 GeV by PHENIX for
both unpolarized and helicity dependent measurements, and comparison to
previous measurements at different sqrt(s) and to NLO pQCD calculations

Speaker: Mr Zhongling Ji (Stony Brook University)

Poster

Video for poster

Zoom link for poster

66 Disentangling the origins of jet modification using Monte Carlos

Jet modification is an essential probe of the quark-gluon plasma produced in heavy-ion collisions. However, current jet modification measurements compare proton-proton and heavy-ion jets that had different properties when they were produced. Extracting the essential modification of jets by the quark-gluon plasma from these measurements requires an in-depth understanding of how jet observables are modified and to what extent they control energy loss. We present an extensive study of how a suite of groomed and ungroomed jet observables are modified and how they impact jet energy loss in Jewel and the hybrid model. We use information available in these models, but not in data, to identify how a jet’s properties after quenching are related to those it had when it was produced. This enables us to focus on those observable features of a heavy-ion jet that provide maximal information about the properties it had before quenching and study the extent to which these conclusions are model-independent. The insights obtained through this model study are a crucial step toward a data-driven analysis of the relation between jet observables and energy loss in experimental data.

Speaker: Quinn Brodsky (Massachusetts Institute of Technology)

HardProbes2020_Poster_QB.pdf

HardProbes_flashtalk.pdf

HardProbes_SupplementalFigs.pdf

Link to Zoom poster presentation

Poster_Preview_Video_QB.mp4

67 Effect of strong magnetic field on the interplay of momentum, heat and charge transports in a hot QCD matter

We have studied the effect of strong magnetic field on the interplay
of coefficients related to the transports of momentum, heat and
charge of a hot QCD matter by shear ($\eta$) and bulk ($\zeta$)
viscosities, thermal ($\kappa$) and electrical ($\sigma_{\rm el}$)
conductivities, and some derived coefficients,
{\em viz.} $\frac{\eta}{s}$, $\frac{\zeta}{s}$, Lorenz (L), Knudsen
($\Omega$), Prandtl (Pl), Reynolds (Rl) numbers and ratio of momentum
diffusion to charge diffusion. We have also computed the
abovementioned coefficients in the absence (isotropic) and presence
of momentum anisotropy caused by the asymptotic expansion at the early stages
of ultrarelativistic heavy-ion collisions, which facilitates us to
compare the effects of anisotropies with respect to the isotropic
medium. We have first calculated the
viscosities, conductivities and entropy density ($s$) in the relaxation time approximation of kinetic theory within the quasiparticle model.
Compared to the isotropic medium, both $\eta$ and $\zeta$ get enhanced
in the presence of strong magnetic field, contrary to their
reduction in expansion-driven anisotropy. $\eta$ increases with temperature
faster in the former case than in the latter case, whereas $\zeta$ in the former case decreases with temperature and in the latter case, it is
meagre and vanishes at a specific temperature. We have also observed that
both $\kappa$ and $\sigma_{\rm el}$ get increased in a strong magnetic field,
but $\kappa$ increases slowly with the temperature,
contrary to its rapid increase in expansion-driven anisotropy,
whereas $\sigma_{\rm el}$ monotonically decreases with the temperature,
opposite to the increase in expansion-driven anisotropy. Thus, the
viscosities and conductivities could distinguish the effects of strong
magnetic field and expansion-driven anisotropy. In the presence of
momentum anisotropies, the entropy density gets decreased, especially it
is lowest in the $B$-driven anisotropy due to reduction of
phase-space. Thus, $\eta/s$ gets enhanced in the $B$-driven anisotropy
and in the expansion-driven anisotropy, it becomes
smaller than the isotropic one. Similarly $\zeta/s$ gets amplified but
decreases faster with the temperature in a strong magnetic field. The
value of the Lorenz number, {\em i.e.}, the ratio,
$\kappa/(\sigma_{\rm el}T)$ in $B$-driven anisotropy is larger than in
isotropic medium, but smaller than in expansion-driven
anisotropy. The Knudsen number gets reduced in expansion-driven anisotropy,
whereas the strong magnetic field raises its value but to less than one, thus the system stays in local equilibrium. The Prandtl number
gets increased in $B$-induced anisotropy, whereas it gets decreased in
expansion-induced anisotropy, compared to isotropic one. Since, Pl is
found larger than 1, the sound attenuation is governed by the
momentum diffusion. The strong magnetic field makes the Reynolds number
smaller than one, whereas the expansion-driven anisotropy makes it
larger. Finally the ratio $(\eta/s)/(\sigma_{\rm el}/T)$ is amplified
much in strong magnetic field, whereas the amplification is less
pronounced in the absence of magnetic field. Since, the ratio is found more than one,
so the momentum diffusion prevails over the charge diffusion.

Speaker: Ms Shubhalaxmi Rath (Indian Institute of Technology Roorkee)

POSTER.I.D.112.pdf

Zoom link for poster

68 Exploring jet quenching through the measurement of dijet momentum balance with ATLAS

High energy partons are known to lose energy when passing through the hot and dense medium produced in heavy-ion collisions. This results in a modification to the transverse momentum distributions of jets. It has been previously shown in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$~TeV that parton energy loss within the Quark Gluon Plasma results in significant modifications to the transverse momentum balance of dijet pairs. However, additional differential measurements are needed to better understand the path-length dependence as well as the role of medium fluctuations to the energy loss. This poster presents the latest measurements of fully unfolded dijet momentum balance in Pb+Pb and pp collisions at $\sqrt{s_{NN}} = 5.02$~TeV. Additionally, the dijet momentum balance in Pb+Pb collisions is measured with respect to the second order azimuthal event plane angle, providing further insight on the path-length dependence to energy loss.

Speaker: Timothy Thomas Rinn (University Of Illinois (US))

hp_2020_poster.pdf

Zoom Meeting Room

69 Heavy flavor production in PbPb collisions : results and prospects

In 2018, LHCb recorded ~210 microbarn^{-1} integrated luminosity of PbPb collisions at sqrt(s_NN) = 5.02 TeV.
Although limited to peripheral hadronic collisions, this new dataset offers unique opportunities to study simultaneously open and close heavy flavor production, at forward rapidity down to zero pT, at the LHC.
Moreover, with an increase of the luminosity by a factor 20 compared to the previous 2015 PbPb dataset, precise measurements on photo-produced charmonia in ultra-peripheral collisions are foreseen.
All these measurements are sensitive to and would help to constrain the small-x parton distribution functions (nPDFs) in the target nucleus.
Finally, the great momentum resolution of the detector allows to study photo-produced J/psi in collisions with a nuclear overlap.
This new type of prob is sensitive to the geometry of the collisions but also to the electromagnetic field of the Pb nuclei.
In this talk, we present the latest results on heavy flavor productions obtained by LHCb measurements in peripheral and ultra-peripheral PbPb collisions.
Prospectives on this first results are also discussed.

Speaker: Samuel Belin (Universita e INFN, Cagliari (IT))

HP2020 poster session Samuel BELIN PosterID = 104

poster_hardprobes_2020.pdf

Poster_presentation_Hard_Probes.mp4

70 Heavy Quark Nuclear Modification at Forward Rapidity in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV

Experimental results from RHIC and LHC show an indication of a mass ordering
on the quark energy loss when crossing the hot and dense medium formed in
A+A collisions. The ordering is more evident at low $p_T$ region, where the
quark mass is more relevant for the energy loss mechanisms. However, this
final-state quark energy loss competes with other effects such as nuclear
shadowing and initial-state energy loss which may also depend on the quark
mass. This presentation is going to show the status of the analysis of charm
and bottom nuclear modification ($R_{AA}$) in the rapidity 1.2$<|y|<$2.2 at
$\sqrt{s_{NN}}$=200 GeV. These  measurements are performed by the PHENIX
forward vertex detectors and muon arms using the $B\rightarrow J/\psi+X$ and
muon decay channels. This rapidity region allows the exploration of
different initial-state effect contributions to the heavy flavor $R_{AA}$.
Besides, the forward measurements have more access to the low-$p_T$ region
because of the additional boost of the non-prompt decay products from heavy
flavor hadrons.

Speaker: Cesar Luiz Da Silva (Los Alamos National Laboratory (US))

Run14AuAu_FVTX_HP_poster.pdf

ZOOM link

71 Heavy Quarkonia in a Magnetic Field

It is predicted that for the noncentral events in
ultrarelativistic heavy-ion collisions (URHICs),
a strong magnetic field is generated at the very early
stages of the collisions. However, as we know
the quarkonia, the physical resonances of $Q \bar Q$
states, are formed in the plasma frame at a time,
$t_F$ (=$\gamma \tau_F$), which is order of 1-2 fm,
depending on the resonances and their momenta.
By the time elapsed, the magnetic field may become
weak. This motivates us to explore the effects of
both the weak and strong magnetic fields on the
properties of heavy quarkonia immersed in a thermal medium of
quarks and gluons and then studied how the magnetic field affects the
quasi-free dissociation in the aforesaid medium.
For that purpose, we have revisited the structure of
gluon self-energy tensor in the presence of both weak and strong
magnetic fields in thermal QCD and obtained the relevant form factors,
that in turn computes the real and imaginary parts of the
resummed gluon propagator. Then the linear response theory yields
the real and imaginary parts of the dielectric permittivity from
the respective resummed propagators. Finally, the inverseFourier transform of the permittivities of the above propagators
in the static limit obtains the complex heavy quark potential.
This is the first study to compute the heavy quark potential
perturbatively in the weak magnetic field as compared to earlier
known study of the strong magnetic field. We have observed
that the real-part gets screened more in the presence of weak
magnetic field, whereas it becomes less screened in the strong
magnetic field compared to their counterparts in the
absence of magnetic field. On the other hand, the magnitude of
the imaginary-part becomes larger both in weak and strong
magnetic field as compared to that in the absence of magnetic
field. Further, the real-part of the
potential is used in the Schr\"{o}dinger
equation to obtain the binding energy, whereas the
imaginary part is used to calculate the
thermal width of heavy quarkonia. With the weak and
strong magnetic field both the observed screening in
the real-part of the potential can be attributedin terms of the decrease in the binding energy, whereas
the increase in the magnitude of the imaginary-part of the
potential will leads to the enhancement of decay
width of quarkonia. Finally we have studied the
quasi free dissociation of quarkonia and found that
the dissociation temperature in the presence of
weak magnetic field becomes slightly lower, whereas
in the presence of strong magnetic field it becomes
higher compared to the one in absence of magnetic
field.

Speaker: Mr Mujeeb Hasan (Indian Institute of Technology Roorkee)

poster_hp2020.pdf

Zoom link for poster

72 Heavy quarkonium suppression beyond the adiabatic limit

Many prior studies of in-medium quarkonium suppression have implicitly made use of an adiabatic approximation in which it was assumed that the heavy quark potential is a slowly varying function of time. In the adiabatic limit, one can separately determine the in-medium breakup rate and the medium time evolution, folding these together only at the end of the calculation. In this paper, we relax this assumption by solving the 3d Schrodinger equation in real-time in order to compute quarkonium suppression dynamically. We compare results obtained using the adiabatic approximation with real-time calculations for both harmonic oscillator and realistic complex heavy quark potentials. Using the latter, we find that, for the $\Upsilon(1s)$, the difference between the adiabatic approximation and full real-time evolution is at the few percent level, however, for the $\Upsilon(2s)$, we find that the correction can be as large as 18% in low temperature regions. For the $J/\Psi$, we find a larger difference between the dynamical evolution and the adiabatic approximation, with the error reaching approximately 36%.

Speaker: Mr Ajaharul Islam (Kent State University)

HP 2020 poster session Ajaharul Islam Poster Id=18

Poster_Hard Probes 2020_Ajaharul Islam.mp4

Poster_Hard Probes 2020_Ajaharul Islam.pdf

73 Implementation of jet and jet-hadron analyses in heavy-ion collisions in Rivet

Rivet (Robust Independent Validation of Experiment and Theory) is a valuable framework for the comparison of data and simulations. Since features required for heavy ion analyses were only recently available, there is a backlog of analyses which need to be implemented. We discuss implementation of heavy ion analyses in Rivet by undergraduates in a Course-Based Undergraduate Research Experience (CURE) in order to address this backlog. Currently, jet analyses in Rivet are restricted to simpler collision systems such as pp or electron-positron.

Complementary tools are currently being developed in order to allow Rivet to analyze jets in heavy-ion collisions. Specifically, the comparison of jet measurements made at the LHC and RHIC to energy loss and flow models is important to understanding of the Quark-Gluon Plasma (QGP). The azimuthal correlations between identified jets and associated particles (jet-hadron correlation) is one observable that can characterize the effects of energy loss of partons in the QGP through their fragmentation.

This contribution presents new Rivet tools for the jet and jet-hadron correlation analyses in heavy-ion collisions. These tools allow analyses to perform jet background subtraction and can take into account $v_{n}$ contributions.

Speaker: William Edward Witt (University of Tennessee (US))

HP2020 poster session Will Witt PosterID = 100

RivetInHIHP2020.pdf

zoom_0.mp4

74 Improved opacity expansion for in-medium branching: transverse momentum dependent distribution

When an energetic parton propagates in a hot QCD medium it loses energy by emitting radiation induced by the parton scattering in the medium. The emission spectrum for such processes is typically split into either a regime dominated by a single hard scattering (GLV) or by a regime dominated by multiple low momentum transfers (BDMPS-Z). Both these regimes admit a close analytic treatment. Only recently, a complete analytic (and systematic) formula was provided which allows to interpolate between these two regimes by expanding around the multiple soft scattering solution. In this talk, we present new results for the $k_t$ differential spectrum. We show that despite the increase in complexity, the formulas are analytically tractable. We compare our approach to the plain opacity expansion and analyse in particular the convergence of the improved opacity expansion by computing the NNLO. Finally, we comment on Monte Carlo implementations for future applications to jet quenching phenomenology.

Speaker: João Barata (BNL and University of Santiago de Compostela/IGFAE)

Barata_final.pdf

Zoom session

75 Incomplete Thermalization and Two-Particle Correlations

We propose a set of correlation and fluctuation observables that, taken together, could indicate the level of equilibration of the matter produced in relativistic nuclear collisions. Theoretical models of the expansion and cooling of QGP used to estimate properties like viscosity and the shear relaxation time generally assume that the QGP reaches local thermal equilibrium. However, it is not likely that experimental systems fully reach this equilibrated state. As a consequence, experimental estimates of QGP properties that rely on theoretical models might yield inaccurate results. We argue that multiplicity fluctuations, transverse momentum correlations, multiplicity-momentum correlations, and correlations of momentum fluctuations are all influenced differently by various physical mechanisms including particle production, viscous forces, initial state fluctuations, and temperature fluctuations. We use simulated proton-proton and nucleus-nucleus collision events to test the behaviors of these observables with respect to the number of particles created in these collisions and attempt to constrain an estimate of the level of equilibration of the matter created in high energy nuclear collisions.

Speaker: Mr Brendan Koch (Lawrence Technological University)

Koch_HardProbes_2June2020.pptx

Microsoft Edge 2020-05-31 02-42-18.mp4

Zoom meeting link

76 Investigating collective flow patterns and the influence of electromagnetic fields in relativistic proton-nucleus collisions

The recent experimental observations of azimuthally anisotropic flow in small systems at RHIC and LHC energies has stimulated a big interest in these collisions, traditionally regarded only as control measurements for heavy-ion collisions and now becoming a new study area for the formation and evolution of the quark-gluon plasma. In the early stage of proton-nucleus collisions extremely intense electromagnetic fields are produced with a magnitude of few $m_{\pi}^2$; unlike symmetric heavy-ion collisions, in these small asymmetric systems the electric field along the impact parameter axis is comparable to the magnetic field perpendicular to the reaction plane. By means of microscopic simulations within the Parton-Hadron-String Dynamics (PHSD) approach we investigate the emergence of collectivity and the influence of electromagnetic fields on final hadronic observables in proton-nucleus collisions at relativistic energy. One of the main effects of the combined asymmetry of electromagnetic fields and particle distributions is a splitting in the rapidity dependence of the directed flow of positively and negatively charged mesons [1].

[1] L. Oliva, P. Moreau, V. Voronyuk and E. Bratkovskaya, arXiv:1909.06770.

Speaker: Lucia Oliva (Institute for Theoretical Physics (ITP), Frankfurt am Main)

Oliva_HP2020_poster.pdf

Oliva_HP2020_video.mp4

Zoom meeting link

77 Jet and Di-jet Underlying Event in p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV at STAR

Proton-ion collisions have been included in runs at the LHC and RHIC in addition to proton-proton and heavy ion collisions as a means of studying cold nuclear matter (CNM) effects. These asymmetric systems have yielded some unexpected trends, notably in measurements of nuclear modification factors at different centralities. Detectors at forward/backward rapidity have been used as a proxy for centrality or event activity (EA) in p+Au collisions in order to avoid auto-correlations in mid-rapidity measurements. In this poster, we show correlations of backward-rapidity (Au-going) event activity with mid-rapidity underlying event (UE) in p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV measured with the STAR detector. We present UE measurements and show the trends of UE in relation to EA for high-transverse momentum ($p_{T}$) jet events vs. di-jet events. Additionally, we will study collision kinematics via observables including jet rapidity ($\eta$) and jet $p_{T}$ as a means of investigating the initial hard scattering of partons in these events.

Speaker: Veronica Verkest (Wayne State University)

https://us02web.zoom.us/j/87900137321

Verkest_HP2020_poster.pdf

Verkest_HP2020_posterVideo.mp4

78 Jet modification with two particle correlations in Au+Au collisions at PHENIX

Two particle correlations which use a high momentum trigger particle are a
useful probe for exploring energy loss in the quark gluon plasma,
particularly in the high multiplicity environment of heavy ion collisions.
Previous direct photon-hadron correlation measurements in PHENIX have
demonstrated the energy loss observed as the suppression of high momentum
particles is redistributed to low momentum particle production at wide
angles from the jet. The direct photon gives access to the kinematics from
the initial hard scattering, which can be used to directly measure the
fragmentation function of the opposing jet. However, it has been observed
that the transition from suppression to enhancement appears at a fixed
associated particle $p_{T}$ rather than at a fixed $z$, the fragmentation
function variable. Recent $\pi^0$-hadron correlations have explored these
modifications more differentially as a function of associate hadron $p_T$
and angular distance, $\Delta\phi$, from the approximated jet axis. This
talk will report on the latest two-particle correlation measurements in
Au+Au collisions compared to p+p collisions from PHENIX, their relation to
fully reconstructed jet measurements and the implications of these
measurements on our understanding of jet energy loss in the QGP.

Speaker: Megan Elizabeth Connors

HP2020Connors_v3.pdf

Zoom Link

79 Light-by-light scattering in ultra-peripheral Pb+Pb collisions in the ATLAS experiment

The ultra-peripheral Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV performed at the ATLAS experiment are used to study a rare light-by-light scattering process,
$\gamma\gamma\rightarrow\gamma\gamma$, allowed in Quantum Electrodynamics via a loop
diagram. The poster summarises recent light-by-light measurements conducted using a combination of 2015 and 2018 datasets recorded by the ATLAS experiment, corresponding to an integrated luminosity of 2.2 n$b^{-1}$. The light-by-light event candidates are required to consist of only two photons produced exclusively, each with transverse energy $E_{\mathrm{T}} > $ 2.5 GeV, pseudorapidity $|\eta| <2.4$, diphoton invariant mass $m_{\gamma\gamma} > 5$ GeV, and with diphoton transverse momentum $p_{\mathrm{T}^{\gamma\gamma}}$ < 1 GeV and acoplanarity below 0.01. The differential distributions, presented as functions of kinematic and angular variables of the final-state photons, are unfolded for detector effects. The fiducial and differential cross-sections are presented and compared with theoretical predictions. The diphoton invariant mass distribution is
used to set limits on the production of axion-like particles.

Speaker: Klaudia Maj (AGH University of Science and Technology (PL))

HP poster session Klaudia Maj Poster ID = 283

KMaj-poster-LbyL.pdf

80 Local Thermalization of Gluons in a Nonlinear Model

Analytic solutions of a nonlinear boson diffusion equation (NBDE) with schematic initial conditions account for the fast local equilibration of gluons in relativistic heavy-ion collisions. The exact solutions are achieved through a nonlinear transformation that was proposed in Ref. [1], but in addition, include the singularity at $\epsilon=\mu<0$, and boundary conditions at the singularity. As a consequence, the analytic time-dependent solutions asymptotically approach the Bose-Einstein distribution not only in the UV, but also in the IR. Calculations are performed with a local equilibration time of $\tau_\text{eq}\simeq 0.1$ fm/$c$ and a local temperature of the order of 600 MeV in the initial stages of Pb-Pb collisions at energies reached at the Large Hadron Collider (LHC). The nonlinear NBDA solutions are suited to replace the conventional linear relaxation-time approximation that enforces equilibration from the initial nonequilibrium to the thermal distribution.

[1] G. Wolschin, Physica A 499, 1 (2018), and preprint (2020).

Speaker: Prof. Georg Wolschin (Heidelberg University)

Local thermalization of gluons in a nonlinear model

Poster56_gw.pdf

zoom_gw.mp4

81 Longitudinal flow decorrelation in Xe+Xe and $p$+Pb collisions with the ATLAS detector

ATLAS measurements of longitudinal flow decorrelation using two- and four-particle correlations for harmonics n=2 and 3 in Xe+Xe and $p$+Pb collisions covering a wide range of transverse momenta and collision centrality are presented and compared with Pb+Pb collisions. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV, Pb+Pb collisions at 5.02 TeV, and $p$+Pb collisions at 5.02 and 8.16 TeV. The energy dependence in $p$+Pb collisions and the system-size dependence of decorrelation are studied. The measurements provide better understanding of the initial state of heavy-ion collisions and will help in developing full three-dimensional initial-state models.

Speaker: Arabinda Behera (Stony Brook University (US))

HP20poster_AB_ver1.pdf

Zoom Link

82 Measurement of $\gamma\gamma\rightarrow\mu^+\mu^-$ pairs in non-ultra peripheral Pb+Pb collisions with the ATLAS detector

ATLAS measurements of dimuons produced via $\gamma\gamma$ scattering processes in inelastic, non-ultra-peripheral Pb+Pb collisions at 5.02 TeV are presented using an integrated luminosity of 1.9 nb$^{-1}$. The $\gamma\gamma\rightarrow\mu^+\mu^-$ pairs are identified via selections on pair momentum asymmetry and acoplanarity, and the contribution from the heavy flavor decay background is estimated using a template fit method. The pair yields are measured differentially as functions of the centrality, average transverse-momentum ($p_T$) and rapidity of the pair. The measurement shows a depletion in the number of muon pairs near zero acoplanarity in central events, resulting in the distributions peaking at non-zero values of acoplanarity. Fits to the perpendicular transverse momentum ($k_\perp$) distributions are used to estimate the centrality dependence of this peak position. The most probable is shown to increase from the most peripheral to the most central collisions, reaching a value of $k_\perp=36\pm1$ MeV in the 0-5\% most-central collisions. The ability of these measurements to qualitatively differentiate between different physical origins of the observed centrality and $p_T$ dependence are discussed.

Speaker: Benjamin Jacob Gilbert (Columbia University (US))

ATL-COM-PHYS-2020-399.pdf

overview.mp4

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83 Measurement of $\Xi_{c}^{0}$ baryon in pp collisions with ALICE at the LHC\

The ALICE detector at the Large Hadron Collider (LHC) has been optimized for studying the strongly-interacting matter - the Quark-Gluon Plasma (QGP) at extremely high densities created in heavy-ion collisions. Charm quarks are produced in initial hard scattering processes, transport through the whole evolution of the system, and interact with the QGP constituents. Therefore, they are powerful probes of the properties of the QGP. The measurement of charmed baryon production in proton-proton collisions provides an important opportunity to test perturbative quantum chromodynamics (pQCD) and to provide insights into the hadronization processes due to the large mass of the charm quark. In addition, the measurement of charmed baryon production is an interesting reference for heavy-ion collisions where the baryon-to-meson ratio can be modified if charm quarks are hadronized by recombination with light quarks in the deconfined medium. The measurement of $\Xi_{c}^{0}$ also provides additional information on the hadronization mechanism of strange quarks in proton-proton collisions.

In this poster, production of $\Xi_{c}^{0}$ is studied in the semi-leptonic decay channel ($\Xi_{c}^{0}\rightarrow e \Xi \nu$) with the ALICE detector using LHC-Run2 data. The $\it{p}_{\rm{T}}$-differential cross section times branching ratio of $\Xi_{c}^{0}$ in proton-proton collisions at $\sqrt{s}$=13 TeV will be shown.

Speaker: Jin Joo Seo (Inha University (KR))

HardProbe2020Poster_jj_v5.pdf

Video.MP4

ZOOM link

84 Measurement of Neutral Mesons in pp Collisions at $\sqrt{s} = 13$ TeV with ALICE

The precise measurement of the neutral meson production in pp collisions can be used as a constrain for fragmentation functions and parton density functions needed by pQCD calculations. Additionally, those measurements can be used as an input for direct photon analyses. Moreover, the dependence of the neutral meson cross section on the event particle multiplicity and on the event sphericity provides a baseline to study the presence of effects that could be interpreted as the creation of the quark-gluon plasma in the collision, as other measurements might indicate.
The reconstruction of neutral mesons via their two photon-decay channel can be realized in the ALICE experiment with several complementary methods, including the calorimeters and the TPC. The combination of these methods allows for a large $p_{\textrm T}$ coverage as well as small statistical and systematic uncertainties.
In this poster, the invariant cross sections as well as the multiplicity and sphericity dependencies of the $\pi^{0}$ and $\eta$ $p_{\textrm T}$ spectra in pp collisions at $\sqrt{s} = 13$ TeV with ALICE will be presented.

Speaker: Joshua Leon Konig (Johann-Wolfgang-Goethe Univ. (DE))

link to zoom meeting for poster session

Poster_Joshua_Koenig_Hard_Probes.pdf

Poster_Video_Joshua_Koenig.mp4

85 Measurement of semi-inclusive jet fragmentation functions in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ =200 GeV in STAR

Jet quenching refers to interaction of the jet shower with the QCD medium (QGP) generated in relativistic heavy ion collisions, which can have multiple phenomenological consequences: jet energy loss; modification of jet substructure; and induced acoplanarity. In this poster we report a measurement of the fragmentation of jets in central and peripheral Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV by the STAR experiment at RHIC, using a semi-inclusive population of jets recoiling from a high transverse momentum trigger hadron. The fragmentation function is constructed from the fraction of the momentum of charged particles projected onto the jet axis over that of the jet. In a previous STAR publication of the semi-inclusive charged-jet spectra, the Mixed-Event technique was used along with the semi-inclusive approach to remove the uncorrelated background contributions [1]. Such techniques have proven to be an excellent tool for isolating contributions from hard-scattered partons, and are now further developed for the measurement of jet fragmentation functions. The fragmentation functions are corrected for uncorrelated background effects and instrumental effects via unfolding, and the results for central and peripheral collisions will be compared. The measurements indicate medium-induced modification of jet fragmentation in heavy ion collisions.

References:
[1] STAR Collaboration, Phys. Rev. C 96 (2017) 24905.

Speaker: Saehanseul Oh (LBNL)

JetFF_HP2020_SaehanseulOh.pdf

Video_JetFF_SaehanseulOh.mp4

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86 Measurement of suppression of large-radius jets and its dependence on substructure in Pb+Pb with ATLAS

Measurements of the jet substructure in Pb+Pb collisions provide information about the mechanism of jet quenching in the hot and dense QCD medium created in these collisions, over a wide range of energy scales. This poster presents the ATLAS measurement of the suppression of yields of large-radius jets and its dependence on the jet substructure, characterized by the presence of sub-jets and their angular correlations. This measurement is performed using the large Pb+Pb data sample at the center-of-mass energy of 5.02 TeV recorded in 2018 and compared to the result from 2017 $pp$ collisions at the same collision energy. This study of the suppression of inclusive yields of large-$R$ jets brings new information about the evolution of the parton shower in the medium and tests the sensitivity of the jet quenching to the color coherence effects.

Speaker: Wenkai Zou (Columbia University (US))

hp2020_poster.pdf

poster_presentation.mp4

Zoom link

87 Measurement of the $\omega$ Meson in pp Collisions at the LHC with ALICE

ALICE is a dedicated heavy-ion experiment and focusses on the properties of the Quark-Gluon Plasma (QGP), a state of strongly interacting matter expected to be formed in heavy-ion collisions.
When performing proton-proton collisions, the energy densities reached are in principle not sufficient to form this medium and hence measurements in this system serve as a baseline to understand the influences of the QGP on the particle production.
Furthermore, cross sections of neutral mesons are needed to test QCD-based theory predictions and to constrain Fragmentation Functions as well as Parton Distribution Functions at high momentum.

This poster will cover the measurement of the invariant cross sections of the $\omega$-meson at mid-rapidity in pp collisions with a center of mass energy of $\sqrt{s}=13\,$TeV produced at the LHC Run2 and measured by ALICE.
The $\omega$ is reconstructed via $\omega \rightarrow \pi^+ \pi^- \pi^0$, where the $\pi^0$ decays further in two photons.
In ALICE, the measurement of photons is performed in two different ways:
The first method measures photons via their energy deposits in electromagnetic calorimeters.
The second method is called PCM (Photon Conversion Method) as photons may convert to e$^{+}$-e$^{-}$ pairs when interacting with the detector material. While the e$^{+}$-e$^{-}$ pairs from conversions are identified and measured with help of the Time Projection Chamber (TPC), the charged pions are measured using information of the Inner Tracking System (ITS) in addition.

Speaker: Jens Robert Luhder (Westfaelische Wilhelms-Universitaet Muenster (DE))

HardProbes2020_Landscape_Poster.pdf

HP2020 poster session Jens Lühder Poster ID = 94

PosterVideo.mp4

88 Measurements of generalized jet angularities in pp collisions at $\sqrt{s} = 5.02$ TeV with ALICE

In recent years jet substructure observables have been used at the LHC as instruments to search for new physics as well as to test perturbative and probe non-perturbative processes in QCD. One such observable, the generalized jet angularity, is of particular interest due its infrared and collinear (IRC) safety and thus calculability from first principles. Its general form has two continuous parameters $\beta$ and $\kappa$, which weight the relative jet constituent angle and $p_T$, respectively. These can be varied along with the jet radius $R$ to recast the observable while maintaining IRC safety, therefore providing various configurations to systematically constrain theoretical calculations. The high-precision capability of the ALICE tracking system allows a unique opportunity at LHC energies to measure tracks with low $p_T$, permitting both accessibility to the softer components inside jets as well as measurement of jets with altogether lower $p_T$. We report the generalized jet angularities in ALICE using pp collisions at $\sqrt{s}$ = 5.02 TeV with charged particle tracks. The parameters $\kappa$ = 1 and $\beta$ = 1, 1.5, 2 are investigated at both large and small values of $R$. Results are presented and compared to theoretical models. These measurements will provide a baseline for comparison to Pb-Pb collisions, where jets are modified due to the QCD medium.

Speaker: Mr Ezra Lesser (University of California Berkeley (US))

Presentation.mp4

Presentation.pdf

Zoom Link

89 Measuring the groomed shared momentum fraction ($z_{g}$) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}= 200$ GeV at STAR using a semi-inclusive approach

Jet quenching is one of the main signals used to investigate the properties of a strongly interacting quark-gluon plasma (QGP). Jet quenching can manifest as more than just energy loss, it can also be seen in the modification of jet substructure. This work focuses on measuring the substructure observable $z_{g}$, a byproduct of softdrop grooming, which probes the physics of the first hard splitting of a hard-scattered parton. This analysis employs a semi-inclusive approach, selecting candidate jets found within the recoil region of a high transverse momentum trigger particle. Requiring a high transverse momentum trigger object induces a surface bias on the event selection, causing selected candidate jets in the recoil region to be biased towards having a longer path length within the medium. Jets with a longer path length in the medium are expected to be more quenched and thus are good candidates to search for modification of $z_{g}$ at RHIC energies. Contribution from combinatorial jets due to the large fluctuating background found in central Au+Au events is subtracted from the signal at the ensemble level, using a mixed events technique. This approach to eliminate combinatorial jet contributions differs from a past measurement of $z_{g}$ at STAR that did not find any modification of $z_{g}$, which imposed a hard core requirement for jet candidates, effectively biasing the selection of jets to have a shorter path-length in the QGP medium and reducing the potential signal for modification of $z_{g}$. In this poster we will present the techniques used and the current preliminary results from the ongoing analysis at STAR.

Speaker: Daniel Nemes (Yale)

Link to Zoom Room

NEMES_HP_POSTER.pdf

VIDEO_NEMES_HP_POSTER.mp4

90 Microscopic Charmonium Production from a Boltzmann+Langevin Approach

We calculate charmonium production in Ultrarelativistic Heavy-Ion Collisions (URHICs) within a semiclassical Boltzmann transport approach for the dissociation and regeneration of charmonium where open charm diffusion is explicitly accounted for. The diffusion of charm quarks is simulated using Langevin dynamics yielding time-dependent quark spectra which serve as input into the regeneration processes of charmonia. The dissociation/regeneration rates for charmonia and relaxation rate for charm quarks are calculated from the same charm-medium interaction. Relative to perturbative rates, a large K-factor (representing nonperturbative interaction strength) is required to account for the phenomenology of open charm observables, which we implement for both the heavy-quark relaxation rate in the Langevin simulation and for the charmonium reaction rates in Boltzmann simulation. Our approach thus establishes a consistent transport framework for the simultaneous evolution of open and hidden heavy flavor with microscopically calculated transport coefficients in both sectors. The first results of phenomenological applications are presented.

Speaker: Xiaojian Du (Universität Bielefeld, Texas A&M University)

HP2020Jpsi_xiaojiandu.pdf

Poster Zoom Link

91 Monte Carlo Studies of Correlations between Leading Hadrons and Jets

Renewed interest in the question of QGP formation in small systems (pp, pA) has revived investigations into whether there is jet modification associated with these collision systems. One such modification of interest is broadening of jet acoplanarity, which is attributed to jet broadening in the medium. While this broadening has not been observed in minimum bias events at the LHC, ALICE data for pp collisions at 13 TeV suggests such an effect may be present in high multiplicity pp events. This broadening cannot be considered as evidence of QGP formation, however, until other possible explanations for its observation are dismissed. A possible contributing effect relates to the spatial distribution of trigger hadrons and the extent to which they serve as proxies for their associated jets. For this purpose, and to address other potential contributing factors, studies of correlations between jets and leading hadrons using PYTHIA 8 will be presented.

Speaker: Caitie Beattie (Yale University)

MCStudiesLeadingHadronsJets_Beattie_updated.pdf

Monte Carlo Studies of Correlations between Leading Hadrons and Jets

PosterVideo_MCStudiesLeadingHadronsJets_Beattie.mp4

92 MPI dependence of the near- and away-side pT spectra for 5 TeV pp, p-Pb and Pb-Pb collisions with the ALICE detector at the LHC

The similarities between pp, p-A and A-A collisions have not been fully understood. One issue when comparing e.g. transverse momentum ($p_{\rm T}$) distributions for different colliding systems at similar mid-rapidity multiplicity, is that selection biases and autocorrelations may play different roles. Recently, the use of the correlation between relatively high-$p_{\rm T}$ tracks ($p_{\rm T}^{\rm leading}>5$ GeV/$c$) and hadrons at lower momenta ($0.5< p_{\rm T}^{\rm associated}<5$ GeV/$c$) has been proposed in order to introduce a new multiplicity estimator. Based on distinct regions defined by $\Delta\phi=\phi_{\rm leading}-\phi_{\rm associated}$, the so-called transverse region, $\pi/3<|\Delta\phi|<2\pi/3$, can be used to build a multiplicity estimator ($N_{\rm T}$) which by definition does not contain the leading and sub-leading jet peaks. In pp collisions simulated with QCD-inspired event generators like PYTHIA, $N_{\rm T}$ is sensitive to Multiple Partonic Interactions (MPI).

This MPI-motivated analysis has been successfully applied to ALICE $\sqrt{s}=13$ TeV pp data; we now extend the study to bigger systems like p-Pb and Pb-Pb collisions. In this work, the $p_{\rm T}$ spectra in the near ($|\Delta\phi|<\pi/3$), away ($|\Delta\phi|>2\pi/3$) and transverse regions will be presented a function of $N_{\rm T}$. Results include measurements for pp, p-Pb and Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. Comparisons among the near and away side $p_{\rm T}$ spectra, at the same $N_{\rm T}$ and $\sqrt{s_{\rm NN}}$, will be shown. The role of auto-correlations and potential effects of MPI in p-Pb and Pb-Pb collisions will be discussed. Comparisons with existing QCD-inspired event generators will be shown.

Speaker: Sushanta Tripathy (Universidad Nacional Autonoma (MX))

Poster169_video_SushantaTripathy.mp4

Poster-ID169_SushantaTripathy.pdf

Zoom meeting link:ID169,Sushanta Tripathy

93 Multiple parton interaction in jets from forward-backward multiplicity correlations

Forward-backward multiplicity correlations have been studied in different colliding system, for all them, the difference with experimental results reveals physical phenomenon not well understood. In this work we present a study of forward backward multiplicity correlations on jets produced in proton-proton collisions using the PYTHIA event generator from UA5 to LHC energías. The analysis is done event by event and event classes according to a jet classification.
We show that color reconnection and multiple parton interaction produce effects which will take into account to explain the experimental data. Furthermore, is shown that from measurements of multiplicity correlations is possible to extract the average number of multiple parton interactions in the event producing these correlations, and albeit model depending, to predict the strength of these correlations, not yet measured, for higher energy collisions.

Speaker: Edgar Dominguez Rosas (Universidad Nacional Autonoma (MX))

HardProbes2.pdf

VideoEdgarPoster.mp4

Zoom Meeting

94 Multiplicity Fluctuations in Relativistic Heavy Ion Collisions

Fluctuations in the multiplicity of particles produced in relativistic nuclear collisions influence many multi-particle correlation measurements. In each nuclear collision, the number of produced particles fluctuates because the number of particle sources fluctuates and the number of particles emerging from each source also fluctuates. Further, we expect that jet and thermal source models of particle production should produce different fluctuation patterns. We search for a method to categorize collision events by the regions of phase space that provide the largest contribution to multiplicity fluctuations. In particular we seek to develop a method for comparison of different collision systems including proton-proton, proton-nucleus, and nucleus-nucleus collisions.

Speaker: Mrs Mary Cody (Lawrence Technological University)

Cody_Video_29May2020.mp4

Multiplicity_Fluctuations_Poster.pdf

Zoom Session Link

95 Multiplicity-Momentum Correlations in Relativistic Heavy Ion Collisions

The observation of anisotropic collective flow in the small systems produced by proton-proton and proton-nucleus collisions at the Relativistic Heavy-Ion Collider and the Large Hadron Collider has led theorists to the hypothesis that hydrodynamics can occur without thermal equilibration. Viscous hydrodynamic flow has the effect of smoothing out fluctuations in particle momenta, but conversely jets have the effect of simultaneously increasing particle number and transverse momentum while inducing fluctuations. We study a new observable that indicates the covariance of multiplicity and momentum of particles produced in nuclear collisions to discover if it can distinguish jet verse hydrodynamic dynamics. This observable is also sensitive to the level of equilibration. We use simulated events of proton-proton and nucleus-nucleus collisions to compare the behavior of our observable for collision events with high and low multiplicities.

Speaker: Mr Mark Kocherovsky (Lawrence Technological University)

HP2020 poster session Mary Cody 311, Mark Kocherovsky 312, Brendan Koch 313

Kocherovsky_HardProbes2020.pdf

MK_HP2020_Video.mp4

96 Neutral pion v2 at low and high pT in Central dAu collisions measured with PHENIX at the RHIC top energies

The observation of multiparticle correlations in heavy ion collisions are usually associated to collective behavior in the formed medium. Recent results at RHIC provide strong arguments for QGP formation in smaller systems.
In this poster, I present the status of the neutral pion second harmonic coefficient v2 as a function of transverse momentum at low and high pT for very central d+Au collisions at 200 GeV. At low pT the v2 is sensitive to the hydrodynamic flow; while at high pT, v2 is sensitive to the in-medium path length dependence thus allowing to constrain qhat.
The data was recorded during the 2016 operational period in PHENIX. The analysis makes use of the central rapidity electromagnetic calorimeter. These results provides strong insight into the dynamics governing the evolution of the fireball at such scales.

Speaker: Carlos Eugenio Perez Lara (Stony Brook University)

HP20_pi0v2_landscape.pdf

HP20_pi0v2.pdf

Zoom link

97 Neutral Pion-Hadron Correlations in Pb-Pb Collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the LHC with ALICE

A longstanding interest in the heavy-ion physics community has been the measurement of jets associated with high $p_{\rm T}$ photons. At leading order, these photons are produced back-to-back with a jet (usually a quark jet), with balanced transverse momentum, during the early stages of the collision. As photons do not interact strongly with the quark-gluon medium, they do not lose energy and thus hard scattering interactions producing them are not subject to a surface bias effect. As a result of these facts, high $p_{\rm T}$ photons provide an unbiased measurement of the transverse momentum of the recoiling jet.

Neutral pions provide the greatest experimental challenge to these ideal measurements, as their decay photons dominate the background to direct photons, and they become increasingly indistinguishable from single photons when measured at higher momenta due to the decreasing opening angle between the decay photons and the finite angular resolution of calorimeters. One solution to this problem is to take measurements with identified $\pi^0$ triggers and subtract them from identical measurements using inclusive electromagnetic trigger, after scaling for the ratio between decay photons and inclusive photons, another important measurement in this area. This analysis provides a foundation for such a project by measuring $\pi^0$-hadron correlations with high $p_{\rm T}$ $\pi^0$s using the ALICE Electromagnetic Calorimeter (EMCal, which also served as an event trigger) and charged particles measured with the ALICE central barrel trackers. These correlations can be analyzed with varying trigger momenta and event centralities. Additionally, the correlations are measured in separate bins of trigger angle with respect to the event plane, both in order to apply the Reaction Plane Fit method for background subtraction and in order to measure path-length dependent modification of jets.

Speaker: Mr Michael Henry Oliver (Yale University (US))

2020-may-31-conference_presentation-hard_probes_2020_poster_pi0hadron_corr_PbPb.pdf

Link to Zoom Room

PosterPi0HVideo_v2.mp4

98 Novel Methods for Measuring the Fragmentation Function of Jets in Heavy Ion Collisions Using Jet-Hadron Correlations

In high energy nucleus-nucleus collisions a novel state of nuclear matter, the Quark Gluon Plasma (QGP) is created. Hard partonic scatterings which happen inside the bulk of this nuclear matter serve as an important probe of QGP properties through their energy loss. An important observable for studying the extent of this partonic energy loss is the jet fragmentation function. Previous studies have shown modification of the fragmentation function of jets in Pb-Pb collisions at the LHC for $\sqrt(s)$ = 2.76 TeV relative to p-p collisions of similar energy. These studies focus on jets with transverse momentum > 85 GeV/c. Detailed investigation of lower momentum jet fragmentation functions may complement these studies by providing more information on energy loss (and thereby more carefully constrain QGP properties). The main difficulty in studying low momentum jets in heavy ion collisions is the presence of a significant uncorrelated background of low momentum hadrons from soft processes which get grouped together with particles from the hard scattering. One way to deal with this background from soft processes is to use the jet-hadron azimuthal correlation to fit and subtract the soft, flow correlated background information from the jet (on the average). This technique allows one to measure the near side yield in the correlation function after background subtraction for a large number of events binned in jet transverse momentum ($p_{T}$) and hadron transverse momentum. From these yields binned in $p_{T}$, one can then construct an uncorrected fragmentation function. We discuss the specifics of this proposed method of measuring the fragmentation function including corrections for detector effects. We present the results of a Monte Carlo study using Pythia and a custom made Heavy Ion Background Generator (along with mocked up detector effects) that demonstrate the feasibility of this method.

Speaker: Charles Hughes (University of Tennessee (US))

Charles_Hughes_HP2020_Poster_Novel_Methods_Frag_Func_PosterID_84.pdf

ZOOM Meeting Link

99 PHENIX measurement of the high pT direct photon production in p+A collisions and its implication to the initial state of the system

High transverse momentum direct photons are penetrating probes in
relativistic heavy ion collisions. Once produced, they leave the collision
region virtually unaffected, even if a hot, dense partonic medium was
formed. This is also the reason why direct photons are immune to the
suppression observed for high pT hadrons and jets in heavy ion collisions,
but can probe the initial state effects. The nuclear modification factor of
high pT photons has been found consistent with unity in Au+Au collisions. It
is of interest whether this applies to not only for p+p and A+A but also for
p+A collisions, especially the most central collisions. Comparing the
centrality dependence of direct photon and hadron production in p+Au system
will provide a test of the applicability of the Glauber model in such
systems which has indeed been an interesting question. The talk will present
the first measurement of high pT photons in this asymmetric collision
system.

Speaker: Niveditha Ramasubramanian (Stony Brook University)

HardProbes2020.pdf

Zoom meeting link

100 PHENIX Results on In-Medium Jet Modification Using $\pi^0$ and Direct Photon-Triggered Two-Particle Correlations

     Jets in $A+A$ collisions are modified both in terms of their particle yield and that they appear broader when compared to their counterparts in $p+p$ collisions. This modification stems from the energy loss of hard-scattered partons traversing the Quark Gluon Plasma (QGP) before fragmenting into jets. Examining the jet modification allows us to study how the jet energy energy diffuses as the hard-scattered partons traverse the QGP, as well as the possible modification of the fragmentation function, $D(z)$, due to energy loss. PHENIX has made new measurements using two particle correlations to study jet modification. By spatially correlating all charged hadrons in an event to a high $p_T$ trigger, one can observe modifications to the yield and angular distribution of the away-side jets peaking opposite the trigger particle direction. $I_{AA}$, the ratio of the away-side integrated yield in $A+A$ to that in $p+p$, is extracted from two-particle correlations. For direct photon triggered two-particle correlations in particular, $I_{AA}$ provides insight into fragmentation function modification as the integrated conditional yields $Y_{AA}$ and $Y_{pp}$ are related to the fragmentation functions, ${D_{AA}}(z)$ and ${D_{pp}}(z)$, i.e.: $I_{AA} = \frac{Y_{AA}}{Y_{pp}}\approx\frac{{D_{AA}(z)}}{{D_{pp}(z)}}$.
     This poster will show the latest two-particle correlation results by PHENIX in $Au+Au$ collisions at $\sqrt{s_{NN}}=200$~GeV collisions, utilizing both the $\pi^0$ and the direct photon as the trigger species. To quantify modification of the recoil jets opposite the trigger particle, measurements of the away-side $I_{AA}$ and Gaussian jet width $\sigma$ will be shown as a function of the associate particle $p_T$. Additionally, a new PHENIX result, the $I_{AA}$ as a function of the separation angle between the trigger and associate particle, $\Delta \phi$, probes modification to the fragmentation function spatially and in $p_T$.

Speaker: Anthony Hodges (Georgia State University)

Hodges_PHENIX_2PC_HP2020.mp4

Hodges_Poster_DPho_2PC_vc.pdf

Zoom Address

101 PHENIX results on quark flavor dependence of flow in Au+Au collisions

An outstanding puzzle in heavy ion physics is the mechanism that generates
collective motion of heavy quarks (charm and bottom) in large collision
systems. The measured azimuthal anisotropy coefficient $v_2$ of electrons
from heavy quarks closely resemble those of light quarks, despite the
several orders of magnitude differences in quark mass. In order to further
understand the quark mass dependence of the flow, we have measure $v_2$ of
electrons from charm and bottom quark decays separately. In contrast to the
apparent heavy quark flow, attempts to measure the $J/\psi$, a charmonium
state, have so far only yielded results consistent with zero. Consistent
understanding of the results will need results with better precision as well
as comparisons with models including quark recombination process. We will
present $v_2$ vs $p_T$ of $J/\psi$ and of electrons originating from charm
and bottom decays measured at mid-rapidity in Au+Au collisions at
$\sqrt{s_{NN}}$ = 200 GeV. Implications for the origins of collective motion
of heavy quarks and quarkonia will be discussed.

Speaker: Takashi Hachiya (Nara Women's University (JP))

hachiya_poster_video.mp4

HPposter_hachiya_v2.pdf

zoom link

102 Probing jet medium interactions via $Z$($H$)+jet momentum imbalances

Different types of high energy hard probes are used to extract the jet transport properties of the Quark-Gluon Plasma created in heavy-ion collisions, of which the heavy boson tagged jets are undoubtedly the most sophisticated due to its clean decay signature and production mechanism. In this study, we used the resummation improved pQCD approach with high order correction in the hard factor to calculate the momentum ratio $x_J$ distributions of $Z$ and Higgs($H$) tagged jets. We found that the formalism can provide a good description of the 5.02 TeV $pp$ data. Using the BDMPS energy loss formalism, along with the OSU 2+1D hydro to simulate the effect of the medium, we extracted the value of the jet transport coefficient to be around $\hat{q}_0=4\sim8~GeV^2/fm$ by comparing with the $Z$+jet $PbPb$ experimental data. The $H$+jet $x_J$ distribution were calculated in a similar manner in contrast and found to have a stronger Sudakov effect as compared with the $Z$+jet distribution. This study uses a clean color-neutral boson as trigger to study the jet quenching effect and serves as a complimentary method in the extraction of the QGP's transport coefficient in high energy nuclear collisions.

arXiv:2001.07606

Speaker: Mr Lin Chen (Central China Normal University)

hp2020poster114.pdf

Link to paper

Link to Zoom

poster114.mp4

103 Probing the partonic degree of freedom in high multiplicity p-Pb at $\sqrt{s_{NN}}$ = 5.02 TeV collisions

The collective flow and the possible formation of the Quark-Gluon Plasma (QGP) in the small colliding systems are hot research topics in the heavy-ion community. Recently, ALICE, ATLAS and CMS collaborations have measured the elliptic flow and the related number of constituent quark (NCQ) scaling of identified hadrons in p+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV, which are important observables to probe the partonic degree of freedom in the created small system.

In this talk, we focus on the coalescence model calculations for the NCQ scaling of at intermediate $p_T$ for the high multiplicity p+Pb collisions, which includes thermal-thermal, thermal-jet and jet-jet partons recombinations, using the thermal partons from hydrodynamics and jet partons after the energy loss of the Linear Boltzmann Transport (LBT) model. Such coalescence model calculations have also been smoothly connected with the low hydrodynamic calculation and with high jet fragmentation. Within such combined framework, we present a nice description of the spectra and elliptic flow over the $p_T$ range from 0 to 6 GeV, and obtain the approximately NCQ scaling at intermediate $p_T$ as measured in experiment. We also switch off the coalescence process of partons and find that without such coalescence, one can not describe the differential elliptic flow and related NCQ scaling at intermediate $p_T$. Such comparison calculations also demonstrate the importance of the partonic degree of freedom and indicate the possible formation of QGP in the high multiplicity p+Pb collisions.

Speaker: Wenbin Zhao (Peking University)

poster_ncq.pdf

ppbncq3.pdf

Zoom link

104 QLBT: The Linear Boltzmann Transport model for heavy quarks with a medium of quasi-particles

Heavy quarks are ideal probes of the QGP matter. To consistently describe the medium evolution and heavy-quark-medium interaction, we improve the linear Boltzmann Transport (LBT) model [Phys. Lett. B777 (2018) 255-259] by modeling QGP as a collection of quasi-particles with equation of state (EOS) fitted to the lattice QCD data. We call this QLBT model, in which the in-medium scatterings of heavy quarks are described using the linear Boltzmann transport that includes both elastic and inelastic energy loss of heavy quarks within the perturbative QCD framework. The temperature dependences of the quasi-particle masses, as well as the strong coupling parameter among them, are systematically extracted from two different sets of lattice EOS (Hot QCD and Wuppertal­-Budapest) with a Bayesian statistical analysis method. With all model parameters fixed by the lattice QCD calculations, QLBT naturally provides a good description of the nuclear modification factors and elliptic flow coefficients of heavy mesons at high transverse momenta. Systematical uncertainties arising from applying two different lattice equations of states are evaluated and turn out to be small for heavy flavor observables.

Speaker: Feng-lei Liu (CCNU)

link

poster.jpg

poster.mp4

105 Recent measurements of the azimuthal anisotropy of prompt $D^0$ mesons in PbPb collisions with the CMS detector at the LHC

In PbPb collisions at the LHC, heavy-flavor (charm and bottom) quarks are predominantly produced at the initial stages of the collision via hard scattering, and they evolve with the whole system. The $D^0$ mesons provide insights on the heavy-quarks and details about the system at initial stages, for example, the potential effects of strong electromagnetic (EM) fields created by collision participants and spectators. In this talk, measurements of the flow harmonics ($v_2$ and $v_3$) of $D^0$ ($\bar{u}c$) and $\bar{D^0}$ ($u\bar{c}$) mesons are presented as functions of rapidity ($y$), transverse momentum, and collision centrality for PbPb collisions at 5.02 TeV, using the large data samples collected by the CMS experiment during the LHC Run 2. The wide rapidity coverage ($|y|<2$) of these new charm mesons measurements allow for a better understanding of the 3-dimensional evolution of the medium formed in heavy-ion collisions. To search for possible effects from strong EM fields created in PbPb collisions, measurements of $\Delta v_2$ between $D^0$ and $\bar{D^0}$ are presented as functions of rapidity. Finally, based on the scalar product method, a four-particle cumulant technique is employed to measure $D^0$ $v_2$ for the first time in PbPb collisions. These results strengthen the evidence of collective phenomena in large hadronic collision systems.

Speaker: Liuyao Zhang (Rice University (US))

HP2020_Poster_Liuyaozhang_final.pdf

zoom_0.mp4

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106 sPHENIX capabilities for jet-based observables

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) benefits from the extensive detector advances driven by LHC and Electron-Ion Collider (EIC) detector R&D. The combination of electromagnetic calorimetry, hadronic calorimetry, precision tracking, and the ability to record data at a very high rates enables measurements of jets, jet substructure, and jet
correlations at RHIC with a kinematic reach that will overlap with similar measurements at the LHC. Jet observables are a particularly useful probe of the Quark Gluon Plasma (QGP) formed in heavy-ion collisions since the hard scatted partons that fragment into final state jets are strongly “quenched”, losing energy to the medium as they traverse it. To answer fundamental questions about the physics of this process, we need to characterize the medium induced modification of the jet fragmentation pattern and the correlation of the lost energy with the jet axis. The measurements require removal of the soft, underlying event (UE), and we will show the performance of different UE subtraction techniques for calorimetric jets in sPHENIX. The performance of the detector for photon-jet and jet fragmentation observables will also be shown.

Speaker: Dennis Perepelitsa (University of Colorado Boulder)

dvp-sPHENIX-HP20-poster-6-2-20.pdf

Virtual Zoom room

107 sPHENIX capabilities for measuring Λc_cc production in Au+Au collisions

A strong enhancement of Λ_c/D⁰ ratio compared to the fragmentation baseline is observed in Au+Au collisions at the top energy of the RHIC. This also suggests that Λ_c may be an important component for the total charm cross section. Precision measurements of charm baryons over a broad momentum range are needed for a detailed understanding of hadronization and parton energy loss mechanisms as well as to characterize QGP transport properties. sPHENIX is a planned next-generation high-rate jet, Upsilon and open heavy-flavor detector at RHIC. A state-of-the-art MAPS-based silicon detector (MVTX) is proposed to enhance heavy flavor detection capabilities greatly. We will present simulation studies of Λ_c baryon measurements in 200 GeV Au+Au collisions utilizing the full sPHENIX tracking capabilities with MVTX. The simulation method for estimating the expected signal and background will be discussed. Statistical projections of the Λ_c/D⁰ ratio will be presented.

Speaker: Yuanjing Ji (University of Science and Technology of China)

sPHENIX_HP20_Lc_wide_v3.pdf

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108 sPHENIX EMCal design, construction and test beam results

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) is designed to accurately study proton-proton, proton-nucleus, and nucleus-nucleus collision systems. The design of sPHENIX, including full azimuthal calorimeter coverage, will allow it to precisely study properties of the Quark Gluon Plasma through open heavy flavor production, jet modification, and Upsilon measurements. It will also perform a variety of cold QCD studies. Helping to enable the broad measurement capabilities of sPHENIX is the Electromagnetic Calorimeter (EMCal), which is the primary detector for identifying and measuring the energy of photons and electrons. The EMCal is constructed of scintillating fibers embedded in blocks of tungsten powder in an epoxy matrix, with the emitted light collected with acrylic light guides and read out through Silicon Photomultipliers (SiPMs). This poster will discuss the design and construction of the EMCal as well the results from a 2018 Beam Test.

Speaker: Anabel Romero (Univ. Illinois at Urbana Champaign (US))

sPHENIX EMCal Design, Construction and Test Beam Results v3.pdf

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109 sPHENIX EMCal module prototyping and production plan in China

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will probe the strongly interacting Quark-Gluon Plasma (QGP) with jets, heavy flavor tagged jets and Upsilon production. The sPHENIX electromagnetic calorimeter (EMCal) detector is essential for these measurements. The Chinese sPHENIX EMCal Consortium includes groups from Fudan, PKU and CIAE, and the consortium is planning to build sPHENIX EMCal modules covering the pseudorapidity range ±(0.8–1.1), significantly extending the experimental acceptance and greatly enhancing the physics capability for jets and Upsilon measurements. We will show the status of the Chinese prototyping project including investigations on the quality of tungsten powder from Chinese vendors and the quality assurance procedures under development. We will also report on the status of our development of a machine to precisely place scintillating fibers automatically.

Speaker: Weihu Ma (Fudan University)

HP2020-Poster-Weihu Ma.mp4

sPHENIX EMCal module prototyping and production plan in China.pdf

ZOOM LINK: sPHENIX EMCal Module Prototyping and Production Plan in China

110 sPHENIX MAPS prototype test beam results

The sPHENIX MVTX detector will be a state-of-the-art monolithic active pixel (MAPS) vertex detector, used by the sPHENIX collaboration, which will allow the study of heavy flavor physics within heavy ion collisions at RHIC. The detector is at an advanced stage of testing with several test beam activities having taken place through 2019. Three test beams have been performed since 2018 to evaluate the physics readiness, the integration of the system with other detectors within sPHENIX (both using four staves, two readout boards and one front end link exchange), and the demonstration of the full readout capability of the minimal detector segment (using eight staves, eight readout boards and one front end link exchange) is expected to be complete by the end the summer of 2019. The results of these tests are being used to drive the collaboration to production-readiness in late 2019 while simultaneously evaluating the track reconstruction software that will be used within the heavy flavor environment experienced by the MVTX.

Speaker: Cameron Dean (Los Alamos National Laboratory (US))

Compressed_HP2020_sPHENIX_MVTX_TB_C_Dean.pdf

HP2020_sPHENIX_MVTX_TB_C_Dean.pdf

sPHENIX vertex detector test beam results

111 Suppression of charmonia states in Pb+Pb collisions at 5.02 TeV with the ATLAS detector.

The suppression of heavy quarkonia states in heavy-ion collisions is a phenomenon understood as a consequence of QGP formation in the hot, dense system produced in high
energy heavy ion collisions. A full assessment of the physics scenario requires a detailed study of effects present in Pb+Pb, in comparison to $pp$ collisions. In this poster, we present the results from the studies of prompt and non-prompt $J/\psi$ and $\psi(2S)$ productions via their di-muon decay channel in 5.02 TeV Pb+Pb collisions collected by the ATLAS experiment at the LHC. We also present in detail how the separation of prompt and non-prompt signal is performed, as well as the description of the systematic uncertainties and technical details of the yield and suppression measurements.

Speaker: Martin Krivos (Charles University (CZ))

poster3.pdf

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112 Testbeam Results for the sPHENIX TPC Prototype

A Time Projection Chamber (TPC) will be the central tracking detector in the sPHENIX experiment. Its main task is to provide a high tracking efficiency and excellent momentum resolution for precise upsilon spectroscopy and jet measurements. The TPC will cover the full azimuth and a pseudorapidity range of up to $\pm$ 1.1.
A small scale prototype TPC with a radial extension of 40 cm and a similar drift length has been manufactured which can accommodate a full size amplification module as for the sPHENIX TPC.
The prototype has been exposed to a 120 GeV proton beam at the Fermilab Test Beam Facility (FTBF). The results of the test-beam campaigns including SAMPA readout electronics will be presented.

Speaker: Henry Klest (Stony Brook University)

HP2020 Klest.pdf

HP2020 Klest.pptx

Klest_Poster_Video.mp4

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113 The dipole picture and the non-relativistic expansion

We study exclusive quarkonium production in the dipole picture at next-to-leading order (NLO) accuracy, using the non-relativistic expansion for the quarkonium wavefunction. This process offers one of the best ways to obtain information about gluon distributions at small $x$, in ultraperipheral heavy ion collisions and in deep inelastic scattering. The quarkonium light cone wave functions needed in the dipole picture have typically been available only at tree level, either in phenomenological models or in the nonrelativistic limit. In this paper, we discuss the compatibility of the dipole approach and the non-relativistic expansion and compute NLO relativistic corrections to the quarkonium light-cone wave function in light-cone gauge. Using these corrections we recover results for the NLO decay width of quarkonium to $e^{+}e^{-}$ and we check that the non-relativistic expansion is consistent with ERBL evolution and with B-JIMWLK evolution of the target. The results presented here will allow computing the exclusive quarkonium production rate at NLO once the one loop photon wave function with massive quarks, currently under investigation, is known. This talk is based on ArXiv:1911.01136

Speaker: Miguel Ángel Escobedo Espinosa (Instituto Galego de Física de Altas Enerxías)

escobedoposter_hp2020.pdf

escobedopostervideo_hp2020.mp4

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114 The NA60+ experiment: high precision measurements of hard and electromagnetic processes at CERN-SPS energies

The energy range covered by the CERN SPS is unique for the investigation of the region of the QCD phase diagram corresponding to finite $\mu_B$. In this talk we will describe the studies for a new fixed target experiment, NA60+, aimed at a precision study of heavy quark and thermal dimuons in Pb-Pb collisions via an energy scan in the interval of incident beam energy 20-160 GeV/nucleon. High statistics measurements of rare processes require interaction rates of $\sim1$ MHz. In addition, a large angular acceptance is required to provide a good coverage around mid-rapidity. The apparatus is designed to reach a mass resolution below 10 MeV in the low mass dimuon region and to collect a statistics $\sim100$ times larger than the original NA60 experiment.
These aspects pose challenging requirements to the apparatus, that will be discussed in the talk, highlighting the original solutions and concepts that will be adopted. Muons will be measured by a spectrometer, including a toroidal magnet based on a new light-weight and general-purpose concept. The system of tracking and triggering devices, covering almost 200 $m^2$, will be based on GEM and RPC detectors, respectively. The system will have to cope a 50-100 kHz dimuon trigger rate, but a triggerless scheme is also under investigation to record all interactions in order to measure simultaneously dimuons and open charm decays in an unbiased way. A silicon spectrometer placed in front of a hadron absorber provides an accurate measurement of the muon tracks, the primary interaction vertex and the secondary decay vertices. This detector will profit from the tremendous advance of monolithic active pixel sensors occurred in recent years. A new R$\&$D will lead to a sensor suited for the operation in a high rate fixed target experiment with ideal features: spatial resolution at the micron level, data rate capability of $\sim$ 100 MHz/s and radiation tolerance exceeding $\sim 10^{14}$ $n_{eq}/$cm$^2$. The stitching technology, available in commercial CMOS imaging processes, will allow the new sensor to reach a wafer-scale area of 15x15 cm$^2$ or even more. This will lead to the possibility to design a practically massless tracker, with all services and connections to outer world confined to the edges of the silicon planes. The implication of the choice of MAPS will be discussed in relation to physics performance, in particular for what concerns the measurement of open cham at low energies.

Speaker: Gianluca Usai (Universita e INFN, Cagliari (IT))

poster-hp-2020-usai-final.pdf

poster-hp-2020-usai-final-with-audio.pptx

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115 The sPHENIX heavy flavor jet physics physics program

Jets initiated by the fragmentation of heavy flavor quarks (HF-jet) are sensitive to collisional energy loss of the high energy parton when traversing through Quark Gluon Plasma. Using the state-of-the-art jet detector at RHIC, sPHENIX, we will perform the first HF-jet measurement at RHIC, which includes the nuclear modification and flow of b-jets, and the momentum balance in di-b-jet pairs. A variety of b-jet tagging algorithms have been developed, which select a HF-jet sample rich in tracks displaced from the primary collision point as measured by the high precision MAPS vertex tracker for sPHENIX. The detection method, physics projection and possible impacts to the field of heavy ion physics will be presented.

Speaker: Dr Jin Huang (Brookhaven National Lab)

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116 The sPHENIX MAPS-based vertex detector

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will study QGP properties with heavy bottom quark jets (B-jets) produced in high-energy heavy ion collisions. B-jets are expected to offer a unique set of observables due to the large bottom quark mass, but need to be measured across an unexplored kinematic regime, particularly at low pT where the expected mass-dependence effects are large but the underlying backgrounds are also high. We will use a three-layer Monolithic-Active-Pixel-Sensor (MAPS) based vertex detector, originally developed for the ALICE ITS upgrade, to identify the signal and suppress the background. The MVTX will serve as the innermost tracking system of sPHENIX, covering 2 cm to 4 cm radially and a pseudorapidity range of |η| < 1.1. The very fine 27 µm x 29 µm pixels allow us to identify B-decay secondary vertices and B-jets in heavy ion collisions with high efficiency and high purity. In this presentation, we show the current status of R&D efforts towards custom readout and mechanical systems to integrate the MVTX detector into the sPHENIX system.

Speaker: Dr Yasser Corrales Morales (Los Alamos National Laboratory (US))

3minPresentation.mp4

sPHENIX_HP2020_poster_MVTX_YCM_v1.pdf

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117 The sPHENIX MAPS-based vertex detector Simulation and Tuning with Test Beam Data

Recent data from RHIC and LHC show that R_AA and v₂ of charm hadrons are very similar to that of light and strangeness hadrons. The R_AA of bottom decay daughters at low p_T seems to be less suppressed than that of light and charm hadrons, suggesting a mass suppression hierarchy. Precision open bottom measurements over a broad momentum range are needed for a detailed understanding of parton energy loss mechanisms and to characterize the transport properties of the strongly-coupled QGP medium. The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will have extensive capabilities for jet and Upsilon measurements. A fast MAPS-based silicon vertex detector (MVTX) is proposed to greatly enhance the heavy flavor detection capabilities of sPHENIX. We will present physics simulation studies on the open bottom measurements within the full sPHENIX tracking environment including the MVTX detector. Open bottom reconstruction has been explored via the inclusive non-prompt D⁰ daughters and the full exclusive reconstruction of B⁺→D⁰π⁺. Statistical projections on the nuclear modification factor and the elliptic flow measurements will be presented.

Speaker: Sitong Peng

sPHENIX_HP2020_poster_MVTX_StP_v2.5.pdf

zoom_1.mp4

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118 Untangling the evolution of heavy ion collisions using direct photon interferometry

Recently, two scenarios have been proposed to resolve the discrepancy between photon yield and the flow coefficients measured in nuclear collisions at RHIC and the LHC. In the first, additional photons are produced from the early pre-equilibrium stage computed from the "bottom-up" thermalization scenario [1-3]. In the second, the thermal rates are enhanced close to the pseudo-critical temperature $T_c\sim 155\,\mathrm{MeV}$ using a phenomenological ansatz [4]. We investigate the measurement of Hanbury Brown-Twiss (HBT) photon correlations [5] as an experimental tool to discriminate between such scenarios. By enhancing standard hydrodynamical simulations with these scenarios, we compute the correlators in terms of the relative momenta of the pair for different values of its transverse momenta, $K_\perp$. We find that the longitudinal correlation is the most sensitive to different photon sources. We compliment this theoretical exploration with a study of the feasibility of measuring a direct photon HBT signal in the upcoming high-luminosity LHC runs. Considering only statistical uncertainties, we find that with the projected $\sim 10^{10}$ heavy ion events a measurement of the HBT correlations for $K_\perp < 1\mathrm{GeV}$ is statistically significant.

[1] J. Berges, K. Reygers, N. Tanji, and R. Venugopalan, Phys. Rev. C95, 054904 (2017), arXiv:1701.05064 [nucl- th]

[2] R. Baier, A. H. Mueller, D. Schiff, and D. T. Son, Phys. Lett. B502, 51 (2001), arXiv:hep-ph/0009237 [hep-ph]
[3] O. Garcia-Montero, (2019), arXiv:1909.12294 [hep-ph]
[4] H. van Hees, M. He, and R. Rapp, Nucl. Phys. A933, 256 (2015), arXiv:1404.2846 [nucl-th]
[5] E. Frodermann and U. Heinz, Phys. Rev. C80, 044903 (2009), arXiv:0907.1292 [nucl-th]

Speaker: Dr Oscar Garcia-Montero (Goethe Universität Frankfurt)

HP_HBT.pdf

Poster.mp4

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119 Validation and improvement of the ZPC parton cascade inside a box

The quark-gluon plasma is formed in high energy heavy ion collisions such as those at RHIC and LHC, where parton interactions greatly affect many final state observables. Both elastic and inelastic parton cascade models have been constructed, such as ZPC, MPC and BAMPS. Recent studies from a multi-phase transport (AMPT) model, which includes the ZPC elastic parton cascade, have shown that even a few parton scatterings in a small system is enough to generate significant momentum anisotropies. It is therefore important to ensure that the parton cascade solution is accurate.

In this work [1], we evaluate and then improve the accuracy of the ZPC parton cascade for elastic scatterings inside a box. It is well known that cascade solutions of the Boltzmann equation such as ZPC suffer from the causality violation at high densities and/or parton scattering cross sections (i.e., large opacities), and that the parton subdivision technique can be used to solve this problem. However, parton subdivision alters the event-by-event correlations and fluctuations and is also much more computationally expensive. Therefore our goal is to find an algorithm that is accurate enough without parton subdivision. We first test a dozen different collision schemes for the collision times and ordering time of ZPC and find that the default collision scheme does not accurately describe the equilibrium momentum distribution at large opacities. We then find a particular collision scheme that can describe very accurately the equilibrium momentum distribution as well as the time evolution towards equilibrium even at high opacities. In addition, we use a novel parton subdivision method to obtain the “exact” time evolution of the moment distribution towards equilibrium. This subdivision method is valid for such box tests and is much more efficient than the traditional subdivision method; e.g. we typically use a subdivision factor of $10^6$ in this study. This work is the first step towards the validation and improvement of the ZPC parton cascade for scatterings in 3-dimensional expansion cases.

[1] X.L. Zhao, G.L. Ma, Y.G. Ma, Z.W. Lin, arXiv:2001.10140.

Speaker: Xinli Zhao (Shanghai Institute of Applied Physics,Chinese Academy of Sciences)

HP2020_poster_xinlizhao2.pdf

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08:50 Break

Plenary: Electroweak and Initial State

Plenary

Convener: Charles Gale (McGill University)

120 Electroweak Probes: Theory Overview

Speaker: Gojko Vujanovic (Wayne State University)

HP20_GV_v4.7.pdf

Recording

121 Electroweak Probes: Experimental Overview

Speaker: Zvi Citron (Ben-Gurion University of the Negev (IL))

HP_zcitron.pdf

Recording

122 Saturation Physics at e-p, e-A and p-A Colliders

Speaker: Matthew Sievert (Los Alamos National Laboratory)

Recording

Sievert_Plenary.pdf

123 Early Time Dynamics and Bulk

Speaker: Bin Wu (CERN)

2020.pdf

Recording

10:45 Break

Parallel: C1 - Jets and High-PT Hadrons III

P2

Convener: Andreas Morsch (CERN)

124 Nuclear Modification of Dijet at EIC

We study the nuclear modification for the dijet cross section in eA deeply inelastic scattering (DIS) process. This nuclear modification comes from multiple scattering of final state parton in a large nucleus, including medium induced radiation. This extra modification to dijet cross section depends on transverse momentum dependent (TMD) quark-gluon correlation function, which can be approximately factorized as large-x TMD quark distribution function and small-x TMD gluon distribution function. The small-x TMD gluon distribution is also related to TMD jet transport coefficient in cold nuclei. With input of the large-x TMD quark distribution, the nuclear modified dijet cross section can be used to probe the small-x TMD gluon distribution/ TMD jet transport coefficient inside the nuclei. The quantitative determination of transport coefficient in cold nuclei will shed light on tranport coefficient of hot and dense quark gluon plasma (QGP). Predictions for dijet cross section at large-x region for EIC collider kinematics are given in this study.

Speaker: Ms Yuanyuan Zhang (Central China Normal University)

HP2020_YYZ.pdf

Recording

125 $\gamma$+jet and $\pi^0$+jet Measurements in Au+Au Collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV with the STAR Experiment

Jets recoiling from a direct photon are seen as a relatively clean probe, due to the more tightly constrained initial hard scattering kinematics compared to di-jet measurements. In this talk, we will present semi-inclusive measurements of jets recoiling from direct-photon and $\pi^0$ triggers in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, both their yield and the transverse momentum imbalance ($x_{J\gamma} = p_{T,Jet}/p_{T,\gamma}$). The dataset used has integrated luminosity 13 nb$^{-1}$ recorded by the STAR experiment in 2014, with isolated photon and $\pi^0$ triggers with 9 $<$ E$^{trig}_T$ $<$ 20 GeV and recoil jets reconstructed with the anti-k$_T$ algorithm. We report fully corrected direct-photon and $\pi^0$-triggered charged recoil jet yields for resolution parameter R=0.2 and R=0.5. A Mixed Event technique developed previously by STAR is used to correct the charged recoil jet yield for uncorrelated background, enabling recoil jet measurements over a broad p$_{T,jet}$ range. The comparison between direct-photon and $\pi^0$-triggered recoil jets is of particular interest because of the access to the different underlying physics between the two cases, such as differences in parton flavor, initial parton energy, and the level of surface bias. We also discuss the radial dependence of in-medium parton energy loss at the top RHIC energy. The transverse momentum imbalance ($x_{J\gamma}$) will be presented for uncorrected full and charged jets (with R=0.4) as compared to baseline expectations. An outlook to $x_{J\gamma}$ with different constituent selections will also be shown.

Speaker: Dr NIHAR RANJAN SAHOO (Texas A&M University)

HP2020_Nihar.pdf

Recording

126 Reconstructed Jet Measurements in p+p, p+Au and Cu+Au collision using PHENIX

In addition to the previously reported inclusive jet spectra and nuclear
modification factors in $d$+Au, and Cu+Au collisions at $\sqrt{s_{NN}}$ =
200 GeV at mid-rapidity, measurements of jets in p+A and jet substructure in
p+p and Cu+Au have also been performed in PHENIX. Jets are reconstructed
from charged particle tracks and electromagnetic calorimeter clusters with
the anti-kT algorithm. The measurements are unfolded for detector response.
While the nuclear modification factor for centrality integrated data in d+Au
collisions is found to be consistent with unity, the centrality-selected
modification factor shows substantial deviations from unity. New
measurements in p+Au collisions will provide crucial information for
understanding the anomalous relationship between hard and soft processes in
$p$/$d$+A systems. Meanwhile the Cu+Au collision system offers an
intermediate testing ground for heavy ion jet reconstruction between small
systems and those with the largest heavy ions. The underlying event in Cu+Au
events is smaller when compared to that in the largest heavy ion systems,
simplifying the extraction of the jet signals, but still achieving the large
energy densities needed to drive substantial in-medium energy loss. To
further explore the modification of the jets in Cu+Au collisions, jet
fragmentation functions and jet grooming studies accessing the jet
substructure have been performed. This talk will present the latest results
from the reconstruction jet studies in PHENIX and their implications for
energy loss in the quark gluon plasma.

Speaker: Milap Patel

hardprobes2020.pdf

Recording

127 String shoving effects on jets in pp, pA and AA collisions

The collective effects in high-multiplicity proton-proton, proton-nucleon and nucleon-nucleon collisions have not yet been attributed to a common mechanism. Within the Lund string model of partons, the interaction force between strings (aka. string shoving) could be responsible for such effects. So far, this aspect has only been present for pp in the existing PYTHIA8 framework, but after the Angantyr model (arXiv: 1806.10820) was implemented, it has been possible to include such a machinery also for pA and AA.

In the previous shoving model implementation for pp (arXiv:1612.05132), only strings parallel to the beam axis were considered for calculating the interaction force. This was a special case since most strings in events with jets do not satisfy this condition and hence, completely dismissed the chance to study possible effects on jets.

Jet observables in dijet events are excellent probes to study collision dynamics in dense systems. Interacting Lund strings will affect jet observables and suggests a new common mechanism responsible for jet modification in pA and AA. In this talk, we present our new implementation of the string shoving mechanism in PYTHIA8 which lets us study the effects on jet observables in pp, pA and AA collisions. We also present preliminary results showing the effects in hadron-jet correlation studies.

Speaker: Smita Chakraborty (Lund University)

HardProbes2020.pdf

Recording

128 Inclusive Jet Measurements in Pb-Pb Collisions at 5.02 TeV with ALICE using Machine Learning Techniques

Measurements of the jet spectra and nuclear modification factors for inclusive charged jets and inclusive full jets (containing both charged and neutral constituents) in Pb-Pb and pp collisions at $\sqrt{s_{NN}} = 5.02$ TeV recorded with the ALICE detector will be shown. These measurements use a novel machine learning based background correction [1] which reduces residual fluctuations. The improved resolution gives opportunity for measurements to lower transverse momenta and larger jet radii $(R)$ than before. In this method, machine learning techniques are used to correct the jet transverse momentum on a jet-by-jet basis using jet parameters such as information about the constituents of the jet. Studies that investigate and estimate the fragmentation bias of this machine learning approach will also be presented. The $R$-dependence of the nuclear modification factor will be shown, which can provide insight as to how jets are modified by the medium and the medium response. Model comparisons will be shown where possible.

[1] R. Haake, C. Loizides, Machine learning based jet momentum reconstruction in heavy-ion collisions, arXiv:1810.06324 [nucl-ex] (2018).

Speaker: Hannah Bossi (Yale University (US))

HBossi_HardProbes2020.pdf

Recording

Parallel: C2 - Electroweak Probes II

Convener: Alexander Milov (Weizmann Institute of Science (IL))

129 Low-$p_{T}$ $\mu^{+}\mu^{-}$ pair production in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV at STAR

In high energy heavy-ion collisions, the strong electromagnetic (EM) fields of the nuclei can produce energetic, high-density photon fluxes, leading to photon-induced interactions. Recently, significant enhancements of $e^{+}e^{-}$ pair and J/$\psi$ production at very low transverse momentum ($p_{T}$) were observed by the STAR [1, 2] and ALICE [3] collaborations in peripheral hadronic A+A collisions. The excess yields exhibit a much weaker centrality dependence compared to the expectation for hadronic production, and are consistent with coherent photon-photon and photon-nucleus interactions. The measured $p_{T}$ broadening for $e^{+}e^{-}$ pairs may indicate the existence of a strong magnetic field in the medium. Measurements with $\mu^{+}\mu^{-}$ pairs provide a complementary channel to investigate these phenomena.

In 2014 and 2016, the STAR experiment at RHIC recorded large samples of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV with di-muon triggers utilizing the Muon Telescope Detector. In this talk, we will present invariant mass and yield distributions as a function of centrality for inclusive $\mu^{+}\mu^{-}$ pair production at \mbox{$p_{T} < 0.15$ GeV/$c$} in the mass range between 2.6 and 10 GeV/$c^{2}$. The $p_{T}^{2}$ distribution of the excess yields for these very low $p_{T}$ $\mu^{+}\mu^{-}$ pairs will also be shown. Physics implications will be discussed together with model comparisons.

References:
[1] J. Adam et al. (STAR Collaboration), Low-$p_{T}$ $e^{+}e^{-}$ Pair Production in Au + Au Collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV and U + U Collisions at $\sqrt{s_{_{\rm NN}}}$ = 193 GeV at STAR, Phys. Rev. Lett. 121, 132301 (2018).
[2] J. Adam et al. (STAR Collaboration), Observation of excess J/$\psi$ yield at very low transverse momenta in Au + Au Collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV and U + U Collisions at $\sqrt{s_{_{\rm NN}}}$ = 193 GeV at STAR, arXiv: 1904.11658.
[3] J. Adam et al. (ALICE Collaboration), Measurement of an Excess in the Yield of J/$\psi$ at Very Low $p_{T}$ in Pb-Pb Collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV, Phys. Rev. Lett. 116, 222301 (2016).

Speaker: Ms Zhen Liu (University of Science and Technology of China and Brookhaven National Laboratory)

HP2020_Low_pT_dimuon_final.pdf

Recording

130 Probing initial- and final-state effects with $\mu^{+}\mu^{-}$ pairs produced from $\gamma\gamma$ scattering in PbPb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the CMS detector

The CMS Collaboration reports on new differential measurements of $\gamma\gamma \rightarrow \mu^{+}\mu^{-}$ production in PbPb collisions at $\sqrt{s_{\rm NN}}$ = 5.02~TeV, using data collected during the 2018 LHC run with an integrated luminosity of 1.6~nb$^{-1}$. Photon-photon interactions have been observed in hadronic heavy-ion collisions by STAR and ALTAS experiments at very low transverse momentum ($p_T$) regions and the measured $p_T$ and azimuthal angular correlations of lepton pairs via $\gamma\gamma$ scattering in hadronic events exhibit significant broadening compared to that from vacuum production in ultra-peripheral events. There is still no consensus on the origin of the observed broadening, which is mainly from $p_T$ hardening of initial scattered photons as impact parameter decreases toward central hadronic collisions or final-state electromagnetic modifications of lepton pairs in presence of a QGP medium. In this talk, the azimuthal angular correlations and mass spectra of $\mu^{+}\mu^{-}$ pairs via $\gamma\gamma$ scattering will be presented as a function of centrality and rapidity. The centrality dependence of $\gamma\gamma \rightarrow \mu^{+}\mu^{-}$ production provides key insight to the origin of observed broadening for photon-photon produced lepton pairs in hadronic collisions while rapidity dependence constrains the relative contributions from leading order and high order photon-photon interactions to measured $\mu^+\mu^-$ pairs.

Speaker: Shuai Yang (Rice University)

HP2020_ShuaiYang_v3.pdf

Recording

131 Measurements of dielectron production in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 27 and 54.4 GeV with the STAR experiment

Dielectron production is suggested as an excellent probe of the hot and dense medium created in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can carry the information from the initial to the final stage of a collision. The study of the dielectron mass spectrum could help to disentangle various contributions. In the low mass region (LMR, $M_{ee}

In this talk, we will present the latest dielectron spectra in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 27 and 54.4 GeV with the STAR experiment. The 1.5 B (1.3 B) minimum-bias events of Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 27 (54.4) GeV taken in 2018 (2017) significantly enhance the precision of the in-medium $\rho$ modification measurement compared to the STAR BES-I results. Lower heavy quark semi-leptonic decay contributions compared to those at top RHIC energies and the large data samples may allow the first extraction of the medium temperature with IMR dielectrons at RHIC. The physics implications of these measurements will be discussed and put into context of previous results.

Speaker: zhen wang (Shandong University)

HP_2020_Dielectron_Zhen_v6.1.pdf

Recording

132 Evidence of shadowing in inelastic nucleon-nucleon cross section

The Glauber modeling plays a key role in centrality-dependent measurements of heavy-ion collisions.
A central input parameter in Glauber models is the inelastic nucleon-nucleon cross section $\sigma_{\rm nn}^{\rm inel}$ which is nearly always taken from proton-proton measurements. At the LHC energies $\sigma_{\rm nn}^{\rm inel}$ depends on the QCD dynamics at small $x$ and low interaction scales where the shadowing/saturation phenomena are expected to become relatively more important for larger nuclei than proton. Thus, $\sigma_{\rm nn}^{\rm inel}$ e.g. in Pb+Pb collisions may well be lower than what is seen in proton-proton collisions.

In this talk we demonstrate how to use the recent $W^\pm$ and $Z$ measurements as a "standard candle" to extract $\sigma_{\rm nn}^{\rm inel}$ in Pb+Pb collisions. Our analysis -- built on the ATLAS data, state-of-the-art NNLO QCD calculations and nuclear PDFs -- indicate that at the LHC energies $\sigma_{\rm nn}^{\rm inel}$ in Pb+Pb collisions is suppressed relative to the proton-proton measurements by tens of percents. We demonstrate that this is in line with expectations from nuclear PDFs.

Speaker: Mr Mikko Kuha (University of Jyväskylä)

Kuha_shadowing_HP2020.pdf

Recording

133 Low-mass dielectron measurements in Pb-Pb collisions with ALICE at the LHC

The production of low-mass dielectrons is one of the most promising tools for the understanding of chiral symmetry restoration and the thermodynamical properties of the Quark-Gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions. For low invariant masses ($m_{\rm ee} <$ 1.1 GeV/$c^{2}$), the dielectron invariant-mass spectrum is sensitive to the properties of short-lived vector mesons in the medium and modifications related to chiral symmetry restoration. Thermal radiation emitted by the system, both during the partonic and hadronic phase, contributes to the dielectron yield over a broad mass range and gives insight into the thermodynamic properties of the medium. In the intermediate-mass region (1.1 $< m_{\rm ee} <$ 2.8 GeV/$c^{2}$), the measurement of thermal dielectrons from the QGP is very challenging at the LHC due to the dominant contribution of correlated e$^{+}$e$^{-}$ pairs from semileptonic decays of charm and beauty hadrons. Finally, at very low pair transverse momenta initial photon annihilation and photonuclear processes, triggered by the coherent electromagnetic fields of the incoming nuclei, are expected to play a role in more peripheral collisions.
In this talk, we will present dielectron measurements with ALICE in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV for different centralities. In particular, the new results obtained analysing 2018 Pb-Pb data, which provide higher statistical precision compared to previous measurements, will be shown. The results will be compared to the expected dielectron yield from known hadronic sources as well as several predictions for the thermal radiation from the hadronic gas and QGP phases.

Speaker: Daiki Sekihata (University of Tokyo (JP))

20200602_HP2020_dsekihat_v10.pdf

Recording

Parallel: C3 - Heavy Flavor IV

Convener: Elena Gonzalez Ferreiro (Universidade de Santiago de Compostela (ES))

134 Pursuing event activity dependence of Heavy flavor and Quarkonium production in small collision systems

Open heavy flavor and quarkonium are valuable probes to identify the underlying QCD dynamics behind high multiplicity events at RHIC and LHC. In previous studies [1,2], we explored $D$-meson and $J/\psi$ production vs. charged hadron multiplicity in $p+p$ and $p+A$ collisions in the CGC framework; we modeled an initial state effect in terms of the fluctuation of gluon saturation scale, $Q_s$. In this presentation, we will pursue further this initial state fluctuation effect at different impact parameters in small collision systems in the impact parameter dependent saturation model. We discuss a systematic analysis of the high multiplicity $p+p$ collisions and centrality biased $p+A$ collisions [3]. We will then discuss how those events could clarify the production mechanism of $J/\psi's$ in high multiplicity events. In particular, we will explore whether the initial state fluctuation effect is capable of changing relative contributions of different intermediate states of heavy quark pairs produced at short distance.

[1] Y. Q. Ma, P. Tribedy, R. Venugopalan, and K. Watanabe, Phys.Rev.D98, 074025 (2018).
[2] Y. Q. Ma, P. Tribedy, R. Venugopalan, and K. Watanabe, Nucl.Phys.A982, 747 (2019)
[3] Y. Q. Ma, T. Stebel, R. Venugopalan, and K. Watanabe, in preparation.

Speaker: Kazuhiro Watanabe (Jefferson Lab)

hp20-KW.pdf

Recording

135 Probing the multi-scale dynamical interaction between heavy quarks and the QGP using JETSCAPE

The dynamics of shower development for a jet traveling through the QGP involves a variety of scales, one of them being the mass for heavy flavors residing inside jets. Though the mass of the heavy quarks plays a subdominant role during the high virtuality portion of the jet, it does affect longitudinal drag and diffusion, stimulating additional radiation from heavy quarks [1]. These emissions partially compensate the reduction in radiation from the dead cone effect. In the lower virtuality part of the shower, when the mass is comparable to the transverse momenta of the parton, scattering and radiation processes off heavy quarks are different than off light quarks. All these factors result in a different nuclear modification factor for heavy versus light flavors and thus for heavy-flavor tagged jets.

The heavy quark shower development and the fluid dynamical medium are modeled on an event by event basis using the JETSCAPE Framework [2]. We present a multi-stage calculation that explores the importance of differences between various heavy quark energy-loss mechanisms within a realistically expanding quark-gluon plasma (QGP). Inside the QGP, the highly virtual and very energetic portion of the shower is modeled using the MATTER generator, while the LBT generator models the energetic and close-to-on-shell heavy quarks’ showering. Energy-momentum exchange with the medium, essential for the study of jet modification, proceeds using a weak coupling recoil approach. The JETSCAPE framework admits transitions, on the level of individual partons, from one energy-loss prescription to the other depending on the parton’s energy and virtuality and the local density. This allows us to explore the effect and interplay between the different regimes of energy loss on the propagation and radiation from hard heavy quarks in a dense medium. The boundary between these stages can be extracted from a comparison with data. We will explore this boundary, via comparisons to experiment, for both charm and bottom quarks.

[1] R. Abir, M. Majumder, Phys. Rev. C 94, 054902 (2016)
[2] J.H. Putschke et al., arXiv:1903.07706

Speaker: Wenkai Fan (Duke University)

Recording

Wenkai_HP2020.pdf

136 Impact of the initial glasma and electromagnetic fields on HQs

Heavy quarks are excellent probes to study the initial stages of heavy ion collisions since they are generated in the early times around 0.1 fm/c together with a thermalization time that is comparable to the lifetime of the QGP phase. In this talk we want to focus on two novel aspects of the HQs dynamics related with the very early stage of their evolution (t< 0.5-1 fm/c). The first is the evolution of HQ distribution in the initial glasma fields w.r.t. the standard HQs interaction with the quark and gluon particles. The second is the impact of the initial strong magnetic field and large vorticity. From the interaction between glasma field and HQs, we find that the field can lead to an initial enhancement of RAA of charm quarks contrary to the pattern of the standard particle interaction; this furthermore leads to a larger elliptic flow v2 after the interaction with the QGP.
In the second part it will be discussed how the strong initial EM field and vorticity can lead to a large directed flow v1 of D0 and anti-D0 and a splitting that depends critically on the time evolution of the magnetic field. In particular, if the large and positive sign of v1 splitting of D mesons measured by Alice Collaboration is due to EM field, then we should expect that the lifetime of EM field at that energy is around 0.4 fm/c. Finally, we propose a study of the effects of EM field on v1 of the leptons from Z0 boson decay and its correlation to the D meson one. We will discuss how this can be exploited to probe if the large directed flow splitting of D meson is truly due to EM field, thus opening a new way to constrain the EM field.
[1] Y. Sun, G. Coci, S. K. Das, S. Plumari, M. Ruggieri and V. Greco, Phys. Lett. B 798, 134933 (2019).
[2] M. Ruggieri and S. K. Das, Phys. Rev. D 98, 094024 (2018).
[3] Y. Sun, V. Greco, S. Plumari, in preparation.

Speaker: Yifeng Sun (INFN-LNS)

Recording

Yifeng-HP 3.pdf

137 Production of $D_{s}^{\pm}$ mesons in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV by STAR

Charm quarks are excellent probes to study properties of the Quark-Gluon Plasma (QGP) created in ultra-relativistic heavy-ion collisions. In particular, measurements of the $D_{s}^{\pm}$ meson production can provide valuable information on the strangeness enhancement in the QGP as well as the charm quark hadronization mechanism in heavy-ion collisions. In this talk, we will present results from the STAR experiment on invariant yields of $D_{s}^{\pm}$ mesons as a function of transverse momentum for different centrality classes of Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The measurements utilize the data with the Heavy Flavor Tracker detector from 2014 and 2016. The ratio between strange ($D_{s}^{\pm}$) and non-strange ($D^{0}$) open charm mesons will also be shown, and compared to PYTHIA and model calculations. A clear enhancement relative to the PYTHIA calculation is seen in the ratio, while model calculations incorporating strangeness enhancement and charm quark coalescence hadronization can describe the observed enhancement reasonably well. These results suggest that recombination of charm quarks with equilibrated strange quarks in the QGP plays an important role in charm quark hadronization.

Speaker: fu chuan (central china normal university)

HP2020_Chuan.pdf

Recording

138 Nuclear modification and exclusive photoproduction of Upsilon in pPb collisions with the CMS experiment

Results of nuclear modification of Upsilon production in pPb collisions at 5.02 TeV and exclusive Upsilon photoproduction in Ultraperipheral collisions (UPC) of pPb at 8.16 TeV, are presented. The nuclear modification factors in pPb collisions are measured to quantify nuclear effects in such a small system and sequential suppression is observed among the three states following the ordering of their binding energies. Exclusive photoproduction of Upsilon states in UPC of protons and Pb using data collected by the CMS in 2016 with an integrated luminosity of $178.4 $ nb$^{-1}$, is presented. The $\Upsilon(1S)$ photoproduction cross-section is extracted in the region $|y|<2.2$ as a function of the photon-proton centre-of-mass energies $W_{\gamma p}$, which provides valuable information of the gluon distribution at small values of parton fractional momenta $x$. The results are compared to other experimental results as well as various theoretical predictions.

Speaker: Dr Ruchi Chudasama (Eotvos Lorand University (HU))

Recording

ruchi_nuclear_mod_upsilon_HP.pdf

Parallel: C4 - Initial State III

Convener: Wei Li (Rice University (US))

139 Recent quarkonium measurements in small systems with the ALICE detector at the LHC

At the LHC energies Multiple Parton Interactions (MPI) are expected to affect not only processes involving soft particle production, but also the hard momentum scales relevant for the production of heavy quarks, such as charm and beauty. Quarkonium measurements in high-multiplicity proton-proton (pp) collisions can shed light on the role of MPI at such hard momentum scales, as well as on the interplay between hard and soft particle production mechanisms. In addition, quarkonium production measurements in minimum bias pp collisions, besides serving as a reference for heavy-ion collisions collected at the same center-of-mass energy, represent a benchmark test of QCD based models in both perturbative and non-perturbative regimes.
The ALICE detector has unique capabilities at the LHC for measuring quarkonia down to zero transverse momentum. Measurements are carried out at both central and forward rapidity, in the dielectron and dimuon decay channel, respectively.
In this contribution, the latest quarkonium measurements performed by the ALICE collaboration in pp collisions at several center-of-mass energies will be presented. Recent $\Upsilon$(1S), $\Upsilon$(2S) and $\Upsilon$(3S) cross section measurements performed at $\sqrt{s}$ = 5 TeV, down to zero transverse momentum and at forward rapidity, will be shown. A comprehensive study of the multiplicity dependence of the quarkonium production at $\sqrt{s}$ = 13 TeV, based on minimum bias and high-multiplicity triggered events, will be also presented. Such measurements include $\psi$(2S) production at forward rapidity as a function of the charged particle multiplicity density, as well as the latest multiplicity dependent inclusive J/$\psi$ production measurements at mid-rapidity, based on multiplicity estimators covering different pseudorapidity regions. Similar multiplicity dependent measurements in p-Pb collisions at center-of-mass energies of $\sqrt{s_{\rm NN}} =$ 5.02 and 8.16 TeV will also be shown. Results will be compared with available theoretical model calculations.

Speaker: Manuel Guittiere (Centre National de la Recherche Scientifique (FR))

HardProbes2020_MG.pdf

Recording

140 PHENIX results on J/psi from small systems

Charmonium is considered a valuable probe to study the medium produced in
collisions involving nuclei and/or nucleons. With the recent observations of
collective behavior of produced particles in small system collisions,
measurements of the modification of charmonium in these systems  have become
increasingly relevant. In this talk we will present the PHENIX results of
J/ measurements at forward and backward rapidities (1.2<|y|<2.2) in p+Al,
p+Au and 3He+Au at = 200 GeV beam energy. These data complement previously
published d+Au data, and comprise the most extensive study of  J/ in small
systems including system size, centrality, transverse momentum and rapidity
dependencies. The observed modifications of J/ production depends strongly
on target size but is very similar for different projectiles. This
presentation will show the conclusion of this experimental effort and
discuss the implication on the current understanding  of charmonia
interaction with nuclear media.

Speaker: Sanghoon Lim (University of Colorado Boulder)

HP2020_shlim_final.pdf

Recording

141 Recent ALICE results on photon-induced J/psi production

The strong electromagnetic fields generated by ultra-relativistic heavy ions provide the possibility to study photon-induced processes at the LHC in new kinematic regions. ALICE has measured the exclusive and the coherent production of J/$\psi$ in p-Pb and Pb-Pb collisions at a center-of-mass energy of 5.02 TeV. These collisions correspond to photon-proton and photon-Pb interactions, respectively. In these cases, the mass of the charm quark allows for perturbative QCD computations addressing the phenomena of saturation and nuclear shadowing.

An overview of recent ALICE results will be presented. The p-Pb data allow us to study the evolution of the cross section for exclusive production over three orders of magnitude in Bjorken-x. Regarding the Pb-Pb data, there are two types of measurements: in ultra-peripheral and in peripheral collisions. The new data from LHC Run 2 allow us to cover a larger kinematic range with smaller experimental uncertainties than in the past. The measurements are compared with the predictions of available models to discuss the implications of the new data for our understanding of QCD in these regimes. A brief summary of ALICE plans in this field for LHC Run 3 and 4 will also be presented.

Speaker: Valeri Pozdniakov (Joint Institute for Nuclear Research (RU))

hp.pdf

Recording

142 ATLAS measurement of azimuthal anisotropies in $Z$-boson tagged $pp$ collisions at 8 and 13 TeV and in ultra-peripheral Pb+Pb collisions at 5.02 TeV

Measurements of two-particle correlations in $pp$ collisions have demonstrated long-range azimuthal correlations between charged particle pairs, commonly interpreted as arising from a single particle azimuthal anisotropy. To better understand the origin and nature of these collective signatures, ATLAS presents studies in $pp$ collisions with a novel handle on the event geometry, and in photo-nuclear collisions.
In $pp$ collisions, the impact-parameter dependence of these correlations are studied by selecting events containing a Z-boson, which acts as an independent handle on the impact parameter.
This talk presents measurements of the azimuthal anisotropy in such Z-tagged $pp$ collisions at 8 and 13 TeV. The measurements include studies of the $p_{T}$, event-multiplicity, and collision energy dependence of the anisotropy as well as the comparison to the inclusive $pp$ collisions.
In addition, two-particle correlations measured in ultra-peripheral Pb+Pb collisions at 5.02 TeV are also presented. In such ultra-peripheral collisions, the nuclei do not interact hadronically. However, a quasi-real photon from the EM field of one nucleus can interact with the other nucleus. These photons may reach energies up to 80 GeV and readily fluctuate into vector meson configurations. Thus these photo-nuclear collisions may proceed as rho-nucleus collisions albeit at a significantly lower collision energy than the equivalent nucleon-nucleon energy.
This talk presents measurements of two-particle correlations and characterizes the azimuthal distribution of particle production in photo-nuclear collisions as a function of the event multiplicity.

Speaker: Blair Daniel Seidlitz (University of Colorado Boulder (US))

BlairSeidlitz_HP2020_SmallSysFlow_FINAL.pdf

Recording

143 Measurement of electroweak-boson production in p-Pb and Pb-Pb collisions at the LHC with ALICE

W and Z bosons are created in the hard scattering processes occurring in the initial stage of heavy-ion collisions and they are insensitive to the presence of a strongly-interacting medium. This makes them clean probes of the initial-state effects of the collision, such as the nuclear modification of the parton distribution functions (nPDFs). The measurement of the electroweak-boson production in p-Pb and Pb-Pb collisions at the LHC provides constraints on the nPDFs of the (anti-)quarks in a phase-space region that is poorly constrained by previous experiments.
ALICE measures the electroweak-boson production in the muonic decay channel at forward rapidities ($2.5 < y_{\rm lab} < 4$). In this contribution, recent results on the Z-boson production in Pb-Pb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV, exploiting the combined 2015 and 2018 data sets, will be presented. The invariant production yield as well as the nuclear modification factor ($R_{\rm AA}$) will be shown as a function of rapidity and collision centrality. Similarly, results on the rapidity dependence of the Z-boson production cross section in p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV will be discussed. The latter will be complemented by new results on the W-boson production cross-section in the same collision system. The different results will be compared to calculations obtained with or without including nuclear modifications of the PDFs, as well as to results obtained by other LHC experiments.

Speaker: Guillaume Taillepied (Université Clermont Auvergne (FR))

HP2020_ewk_bosons_ALICE.pdf

Recording

12:40 Break

Parallel: D1 - Jets and High-PT Hadrons IV

P2

Convener: Leticia Cunqueiro Mendez (Oak Ridge National Laboratory - (US))

144 The wake of jets from linearized hydrodynamics

Recently, jet substructure observables have been widely used in the study of jets. Some observables are sensitive to the wide angle soft particles within the jet, for example, the Lund plane distribution with different jet radii and soft drop parameters. As the jet loses energy and momentum during its evolution inside the quark-gluon plasma (QGP), the “lost" energy and momentum is deposited in the medium and evolves therein — the wake of the jet. This wake ultimately hadronizes into particles whose net momentum must be correlated with the jet direction, since it corresponds to the momentum lost by the jet. This means that when a jet reconstruction algorithm is then used to find the jet, some of the particles originating from the wake must end up being counted as a part of the jet. Since these particles are generally soft, and are spread over a wide angle with respect to the jet axis, they can significantly modify those jet substructure observables that are sensitive to the soft physics and/or to physics at wide angles. To understand the predictions of any model of jet quenching for such observables, it is mandatory to quantify the dynamics of the back-reaction of the medium to the jet, namely the wake of the jet.

In this talk, we will report progress toward addressing this question by treating the energy and momentum loss as a perturbation on the background of a Bjorken flow. By working to linear order in the perturbation and solving the resulting evolution equations numerically in momentum space, we study how the wake evolves within the hydrodynamically evolving droplet of QGP and explore the dependence of the dynamics of the wake on the viscosity of the QGP and model uncertainties. Via this study, we upgrade the previous numerical implementation of the jet wake in the hybrid model, in particular for the component of the wake that yields particles with transverse momenta of a few GeV after hadronization. Further we will assess the phenomenological impact of the improved wake treatment on a range of jet observables.

Speaker: Prof. Jorge Casalderrey Solana (University of Barcelona)

jcs_hp2020.pdf

Recording

145 Fragmentation and equilibration of jets in a QCD plasma.

We investigate the medium induced fragmentation of jets in a high-temperature QCD plasma. Based on an effective kinetic theory of QCD, we study the non-equilibrium evolution of the jet shower and the chemical equilibration of jet fragments in the medium. By including radiative emissions as well as the elastic interactions evolution, our approach extends all the way from the jet energy scale to the temperature of the medium and includes important effects such as the recoil of the medium. We present results for the in-medium fragmentation, including chemical and kinetic equilibration of the soft fragments and discuss implications of our result to jet quenching physics and the problem of thermalization of the quark-gluon plasma in heavy ion collisions.

Speaker: Mr Ismail Soudi (Universität Bielefeld)

Fragmentation and equilibration of jets in a QCD plasma..pdf

Recording

146 Jet quenching tests of the QCD Equation of State

Jet quenching has become a fundamental tool to study
the hot QCD matter produced in heavy ion collisions. While
important theoretical and experimental advances have been made in the last two decades, the extraction of the medium properties
and the comparison with finite temperature QCD is still particularly worrisome.
In this work we show that improvements in the calculation of the medium-induced
gluon spectrum are required for a correct extraction of these parameters without temperature issues. In particular, we employ an improved numerical implementation of multiple scatterings that resums all possible terms in the opacity expansion beyond the Gaussian approximation. We find significant differences in the extracted medium parameters when comparing with two of the most used approximations in phenomenological analyses to date, the first order opacity expansion and the Gaussian approximation. We also make a first attempt to compare the extracted medium parameters with lattice results.

Speaker: Xabier Feal (BNL)

HP2020-Feal.pdf

147 A study of Jet Quenching properties using JEWEL framework coupled with v-USPhydro forhydrodynamic simulation along TRENTo and MC-KLN initial conditions

High energy partons has been a useful tool to study the hot and dense matter produced in heavy-ion collisions. To this end, it has been shown that is important to incorporate the most realistic description of the Quark Gluon Plasma using relativistic hydrodynamics in order to study many properties at high pT. Therefore, in this work we couple a modified JEWEL code to event-by-event relativistic hydrodynamics (v-USPhydro). Here we compare two different event-by-event initial conditions TRENTO and mckln coupled to a full 2+1 hydrodynamic model to smooth Glauber initial conditions with only a Bjorken longitudinal expansion. The jet v2 and v3, substructure, and shape variables are calculated for LHC PbPb 2.76TeV collisions. We find that vn's have the largest influence from a realistic medium.

Speaker: Mr Fabio Canedo (Universidade de São Paulo)

presentation.pdf

Recording

Parallel: D2 - Heavy Flavor V

Convener: Che-Ming Ko

148 $J/\psi$ production in jets in p+p collisions at $\sqrt{s}$ = 500 GeV by STAR

The suppression of $J/\psi$ production caused by the color-screening effect in heavy-ion collisions is considered as an evidence of the creation of quark-gluon plasma. To interpret the observed suppression in heavy-ion collisions, a good understanding of its production mechanism in p+p collisions is needed. However, the production of $J/\psi$ in hadronic collisions remains not fully understood and requires further studies. Recently, $J/\psi$ production in jets was proposed as a useful observable to help explore the $J/\psi$ production mechanism, and to differentiate various $J/\psi$ production models.

In this talk, we will present the measurement of the fraction of charged jet transverse momentum ($p_{T}$) carried by the $J/\psi$ meson, z($J/\psi$) $\equiv$ $p_{T}(J/\psi)$/$p_{T}(jet)$, at mid-pseudorapidity ($|\eta|<1$) with a kinematic cut of $p_{T}(J/\psi)>$5 GeV/c in p+p collisions at $\sqrt{s}$ = 500 GeV by the STAR experiment. The comparison to model calculations and similar measurements carried out at the LHC will be presented, and its physics implications will be discussed.

Speaker: Dr Qian Yang (Shandong University)

Qian_HPs_final.pdf

Recording

149 Bottomonia in QGP from lattice QCD: Beyond the ground states

Using novel lattice (non-relativistic) QCD techniques, we will present results pertaining to the fate of Υ(1S), Υ(2S) and Υ(3S) in QGP. We will present results on how the masses of these states change with temperature, as well as how their spatial sizes change. Finally, we will also show new lattice QCD results on the heavy quark potential from Wilson lines.

Speaker: Rasmus Larsen (Brookhaven Nationanl Laboratory)

Recording

wavefunctions_talk.pdf

150 Quarkonia production in pPb collisions

We present LHCb results on quarkonia production in proton-lead collisions, using the data collected in 2016 at sqrt(s_NN) = 8.16 TeV. Measurements are performed in the forward rapidity region (pseudorapidity between 2 and 5), covering both forward (pPb configuration) and backward (Pbp configuration) rapidities. Measurements for charmonium states include prompt and from-b-decay components which are disentangled. The large increase of the data sample, with respect to the 5 TeV sample collected in 2013, allows a remarkable improvement in the accuracy of the studies of nuclear matter effects.

Speaker: Óscar Boente García (Universidade de Santiago de Compostela (ES))

HP2020_oboente.pdf

Recording

151 Z production in pPb collisions at LHCb

LHCb measurements of the electroweak boson production in forward and backward configuration of proton-lead collisions are sensitive to the nPDFs in a unique kinematic domain, allowing to study in a complementary fashion the structure of the nucleus.
In this talk, we present the latest results obtained on the Z production in pPb and Pbp collisions by LHCb, being the most precise measurements in the rapidity coverage

Speaker: Hengne Li (South China Normal University (CN))

20200602_HengneHardProbeZ_v2.pdf

Recording

Parallel: D3 - Heavy Flavor VI

Convener: Enrico Scomparin (Universita e INFN Torino (IT))

152 Directed, elliptic and triangular flow of D mesons in ALICE

Heavy quarks (charm and beauty) are produced in abundance during the early stage of ultra-relativistic heavy-ion collisions. They therefore experience the full evolution of the Quark-Gluon Plasma (QGP). This makes them unique probes of the collective behaviour of particles in the medium as it expands and cools. The anisotropy of the overlap region between the two colliding nuclei in the initial state is translated into a momentum anisotropy of the produced particles in the final state.

The $v_{2}$, or elliptic flow, is an observable that reflects the degree of collectivity in this expanding system. At low momenta it provides information on the collective motion of particles and the degree of thermalisation within the system, while at higher momenta it serves to constrain the path-length dependence of the energy loss of heavy quarks in the medium. The effect of quark recombination can be studied by comparing the measured $v_{2}$ of non-strange D mesons (${\rm D}^0$, ${\rm D}^{+}$, ${\rm D}^{*+}$) with measurements of strange D mesons (${\rm D}_{\rm s}^{+}$).

In addition to the elliptic flow, other flow harmonics provide information about the properties of the QGP. The directed flow ($v_{1}$) of heavy-flavour particles is sensitive to the unprecedentedly strong magnetic fields present in the early stages of the collision, and so measurements of its charge dependence are key to constraining the electrical conductivity of the QGP. Finally, the triangular flow ($v_{3}$) is driven by fluctuations in the initial state of the system, and is sensitive to the ratio of the shear viscosity to the entropy density, $\eta/s$. The $v_3$ measurement therefore serves as an important constraint on hydrodynamic models of QGP formation, which predict a low $\eta/s$ at RHIC and the LHC.

This talk will present the latest measurements by the ALICE Collaboration on the directed, elliptic and triangular flow of charmed hadrons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. The charge-dependent $v_1$ of D$^0$ mesons will be shown, as well as the average D-meson $v_{2}$ measured by standard and Event-Shape Engineering (ESE) techniques, and the non-strange D-meson $v_{3}$. The non-strange D-meson $v_{2}$ results will also be compared with those of strange D mesons. Comparisons with predictions from theoretical models will be discussed.

Speaker: Stefano Trogolo (Universita e INFN, Padova (IT))

Recording

Trogolo_HP_2020_final.pdf

153 Heavy Quark Radiative Energy Loss in a Non-perturbative Approach

The energy loss of heavy quarks propagating through the quark-gluon plasma (QGP) is expected to transit from an elastic regime at low and intermediate momenta to a radiative regime at high momenta. For the latter, a significant amount of energy dissipates by radiating rather soft gluons that can strongly interact with the surrounding medium through non-perturbative many-body effects. In order to investigate these effects, we extend a T-matrix approach [1-3], which describes the equation of state of QGP and yields a small shear viscosity and heavy-quark diffusion coefficient, to include the radiative energy loss of heavy quarks. We analyze several different cases by turning on/off specific non-perturbative many-body effects, to illustrate how the underlying partonic spectral functions and drag coefficients affect the radiation properties, such as the emitted power spectra and the pertinent transport coefficient, qhat. In addition, by scrutinizing the power spectrum, we can test the accuracy of the commonly employed soft and collinear approximations for the kinematics of the radiated gluons. Furthermore, we implement the transport coefficients including both the elastic and radiative contributions into a realistic transport simulations. The comparison of the results to other approaches and experiments will be discussed.

[1] S. Y. F. Liu and R. Rapp, (2016), arXiv:1612.09138 [nucl-th].
[2] S. Y. F. Liu and R. Rapp, Phys. Rev. C 97, 034918 (2018).
[3] S. Y. F. Liu, M. He, and R. Rapp, (2018), Phys.Rev. C99, 055201 (2019).
[4] S. Y. F. Liu, and R. Rapp, (2020), in preparation.

Speaker: Dr Shuai Liu (Institute of Modern Physics)

eloss_sliu_HP.pdf

Recording

154 Heavy flavor physics with the sPHENIX MAPS vertex tracker upgrade

The sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will measure a suite of unique jet and Upsilon observables with unprecedented statistics and kinematic reach at RHIC energies. A MAPS-based vertex detector upgrade to sPHENIX, the MVTX, will provide a precise determination of the impact parameter of tracks relative to the primary vertex in high multiplicity heavy ion collisions. The MVTX utilizes the latest generation of MAPS technology to provide precision tracking with high tracking efficiency over a broad momentum range in the high luminosity RHIC environment. These new capabilities will enable precision measurements of open heavy flavor observables, covering an unexplored kinematic regime at RHIC. The physics program, its potential impact, and recent detector development of the MVTX will be discussed in this talk.

Speaker: Michael Joseph Peters (Massachusetts Inst. of Technology (US))

hp2020_MVTX_HF_f.pdf

155 Heavy-flavour studies with a high-luminosity fixed-target experiment at the LHC

Extraction of the multi-TeV proton and lead LHC beams with a bent crystal or by using an internal gas target allows one to perform the most energetic fixed-target experiment ever. $pp$, $pd$ and $pA$ collisions at $\sqrt{s_{NN}}=115$ GeV and Pb$p$ and PbA collisions at $\sqrt{s_{NN}}=72$ GeV can be studied with high precision and modern detection techniques over a broad rapidity range.
Using the LHCb and ALICE detectors in a fixed-target mode offers unprecedented possibilities to access heavy-flavour production in a new energy domain, half way between the SPS and nominal RHIC energies.

In this talk, we will review projection studies for quarkonium and open charm and beauty production with both detector set-ups used with various nuclear targets and the LHC lead beams.
We will also discuss prospects of novel observations, e.g. $\chi_{C}$ suppression measurements and new quarkonium-correlation studies.

Speaker: Dr Barbara Antonina Trzeciak (Czech Technical University in Prague)

Recording

Trzeciak_AFTER_HP20_v2.pdf

Parallel: D4 - Initial State IV

Convener: Jacquelyn Noronha-Hostler (Rutgers University)

156 Dependence of semi-inclusive jet and high-$p_{T}$ charged particle production on event activity at high backward-rapidity in $\sqrt{s_\mathrm{NN}}$ = 200 GeV $p$+Au collisions at STAR

Observations of flow-like signals in small-system collisions, $pp$ and $p$/$d$+A, have led to a resurgence of interest and measurements, the results of which have perhaps permanently challenged the naive picture of initial geometry and subsequent early-time dynamics for these systems. In the wake of this renewed interest, jet and high-$p_\mathrm{T}$ particle measurements in small systems are proving similarly fruitful and challenging. While no clear signal of jet quenching has been observed, inclusive measurements at both LHC and RHIC energies of $p$/$d$+A collisions show jet spectra enhancement/suppression at high Bjorken-$x$ when binned by event activity (EA) at high backward-rapidity (the A-going direction). In this talk we present the first semi-inclusive small-system jet spectra measurements at RHIC energies. The results show significant suppression of the jet spectra normalized per trigger in high-EA relative to low-EA collisions. PYTHIA 8 simulations verify that the modification of these spectra is not the result of trivial autocorrelations. Surprisingly, these simulations do show a qualitatively similar modification and studies to understand the cause will be presented. Finally, we present charged particle correlations with EA at high backward-rapidity, which hint at energy conservation or fluctuating proton effects.

Speaker: David Stewart (Yale University)

HP2020_Final.pdf

Recording

157 Fully coherent energy loss effects on light and open heavy-flavour hadrons in pA collisions

Fully coherent energy loss (FCEL), predicted from first principle QCD calculations, affects the yields of hadrons in proton-nucleus collisions at all energies. The FCEL effects on quarkonia have been succesfully compared to existing measurements over the last few years. In this talk, our approach is generalized systematically to $2\to 2$ processes allowing for the first computation of FCEL effects on light ($h^\pm$) and open heavy-flavour ($D$, $B$) hadron production in pA collisions at the LHC. Results indicate that significant FCEL effects are to be expected, at mid-rapidity and even more so at forward rapidity, and should be taken into account in the standard nPDF global fit analyses. The FCEL baseline calculations are provided and compared to data whenever available.

References:
F. Arleo and S. Peigné, to appear
F. Arleo, F. Cougoulic, S. Peigné, to appear

Speaker: Francois Arleo (Laboratoire Leprince-Ringuet)

Hard_Probes_2020_Arleo.pdf

Recording

158 Probing the gluonic intial state with inclusive dijets in pPb and exclusive dijets in ultra-peripheral PbPb collision at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the CMS experiment

Dijet processes can be used in several ways to probe the nuclear initial state. Exclusive dijet photoproduction in ultra-peripheral heavy-ion collisions has recently been suggested as a probe of the gluon Wigner distribution. In particular, the angular correlation of exclusive dijets can asses the azimuthal anisotropy of the gluon distribution in the nuclear target. In this talk we present, for the first time, the measurement of the angular correlations of dijets in ultra-peripheral PbPb collisions at $\sqrt{s_{\rm NN}}$ = 5.02~TeV with the CMS experiment. The dependence of the second harmonic of the angular distribution as a function of the vectorial sum of the leading and subleading jets will be discussed. In addition, the pseudorapidity of the inclusive dijet system in pPb collisions is a probe of the nuclear parton distribution function (nPDF) of the gluon: the recent CMS result will be presented, and its impact on nPDF models will be discussed.

Speaker: Aleksandr Bylinkin (The University of Kansas (US))

Bylinkin_HP_2020_final.pdf

Recording

159 Probing gluon saturation through precision studies of inclusive dijet and photon+dijet production in e+A DIS at small x

We present the first computation of the next-to-leading order (NLO) impact factors for inclusive dijet and photon+dijet production in e+A DIS at small $x$ in the framework of the Color Glass Condensate (CGC) effective field theory. When combined with the recent derivation of JIMWLK small $x$ evolution to next-to-leading logarithm in $x$ accuracy, these results provide us with a prediction of the photon+dijet and dijet cross-sections in e+A DIS to O($\alpha_S^3 \ln(1/x)$) accuracy. The novel momentum space computational techniques developed in our work allow us to extend our work to higher loop orders and we will discuss the progress towards that direction in the context of inclusive dijet production.
This methodology can also be employed in precision computations for p+A collisions and the realization of these precision studies at small $x$, both for DIS and hadron-hadron (nucleus) collisions, will pave the way towards the quantitative global analyses of data required for a definitive understanding of the systematics of gluon saturation.

Speaker: Kaushik Roy

Recording

Roy_HP2020_final.pdf

Wednesday 3 June

Plenary: Jets I

Plenary

Convener: Marta Verweij (Nikhef National institute for subatomic physics (NL))

160 Jet: Overview

Speaker: Eliane Epple (Los Alamos National Laboratory (US))

HP20_JetOverview_Epple_Final.pdf

Recording

161 Jets: Medium Modifications

Speaker: Jasmine Brewer (Massachusetts Institute of Technology)

JasmineBrewer-HP2020.pdf

Recording

162 Jets: Substructure

Speaker: Yang-Ting Chien (Stony Brook University)

Chien_HP2020.pdf

Recording

08:45 Coffee break

Plenary: Jets II

Plenary

Convener: Xin-Nian Wang (Central China Normal University (China)) / Lawrence Berkeley Na)

163 Jets: Back Reaction onto the Medium

Speaker: Yasuki Tachibana (Wayne State University)

hp_2020.key.zip

hp_2020.pdf

Recording

164 Monte Carlo Modeling

Speaker: Kolja Kauder (Brookhaven National Laboratory)

Kauder_MonteCarlo_HP2020.pdf

Recording

165 Multi-Parton Interactions and Underlying Event: A PYTHIA Perspective

Speaker: Christian Bierlich (Lund University (SE))

cbierlich.pdf

Recording

10:15 Break

Parallel: E1 - Jets and High-PT Hadrons V

P2

Convener: Yen-Jie Lee (Massachusetts Inst. of Technology (US))

166 Measurement of jet structure and substructure in heavy ion collisions with ATLAS

Measurement of jet structure in heavy-ion collisions allows studying properties of the hot and dense QCD medium created in these collisions and the mechanism of the jet quenching. This talk presents the latest ATLAS measurements of the internal structure of jets to better constrain the modifications of the parton showering process. A new measurement of how the suppression of large-radius jets depends on the internal jet structure characterized by the transverse momentum scale for the hardest splitting will be presented. This measurement brings new information about the evolution of the parton shower in the medium and tests the sensitivity of the jet quenching to color coherence effects. Furthermore, a measurement of the angular distribution of charged particles around the jet axis in Pb+Pb and $pp$ collisions at $\sqrt{s_{NN}} = 5.02$~TeV will be presented. This measurement is performed for jets with radius parameter $R = 0.4$ but is extended for particles outside the jet cone to a radial distance of 0.8.

Speaker: Anne Marie Sickles (Univ. Illinois at Urbana Champaign (US))

Recording

sickles_060320.pdf

167 Jet substructure measurements in Pb-Pb collisions at 5.02 TeV with ALICE

We report new jet substructure measurements in Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector. For the first time, fully corrected measurements of the groomed jet momentum fraction, $z_g$, the groomed jet radius, $\theta_g \equiv R_g/R$, and the number of Soft Drop splittings, $n_{\mathrm{SD}}$, will be shown in Pb-Pb collisions, along with their ratio to those in pp collisions. We present results with the Soft Drop grooming method for multiple grooming settings, as well as with the Dynamical grooming method. By using stronger grooming conditions and improved background subtraction techniques, these results are fully corrected and can be directly compared to theoretical models of jet quenching - avoiding the large background contamination present in previously reported observables. Additional jet substructure measurements will be shown and compared to recent theoretical predictions, featuring the Lund plane map of radiation phase space and its projections onto distributions of the splitting scale $k_T$, and the angular distribution between the groomed and ungroomed jet axis.

Speaker: James Mulligan (University of California, Berkeley (US))

Mulligan_HP2020.pdf

Recording

168 Jet substructure via dynamical grooming

Jet substructure represents a cornerstone in the on-going endeavor to pinpoint the effect of a hot, thermal medium, namely the QGP, on QCD dynamics. In this talk, based on [1], I will present a new set of jet substructure observables and an associated grooming technique, dubbed "dynamical grooming". This procedure is rooted on identifying the hardest splitting in an angular ordered shower and discarding prior splittings that occur at larger angles. First, I will use p+p collisions to benchmark the method with pQCD calculations through the computation of the Sudakov form factor at modified leading-log accuracy in the context of vetoed showers. I will compare the analytic properties of the dynamically tagged splitting such as its momentum sharing fraction with Monte-Carlo simulations. In addition, the resilience of the method to non-perturbative effects together with its performance on quark/gluon discrimination and boosted W/t/H tagging will be assessed. Finally, predictions for the dynamically groomed $z_{g}$ in heavy-ion collisions at LHC energies will be presented within a probabilistic picture of energy loss.

[1] arXiv:1911.00375

Speaker: Alba Soto Ontoso (Brookhaven National Lab)

HardProbes2020_ASO.pdf

Recording

169 Nuclear modification of jet shape for inclusive jets and γ-jets at the LHC energies

With our coupled jet-fluid model [1, 2, 3], we study the nuclear modifications of full jets and jet structures for single inclusive jets and $\gamma$-jets in Pb+Pb collisions at $5.02$ ATeV and $2.76$ ATeV. The in-medium evolution of full jet shower is described by a set of coupled transport equations including the effects of collisional energy loss, transverse momentum broadening and medium-induced splitting process. The dynamical evolution of bulk medium is simulated by solving relativistic hydrodynamic equation with source term which accounts for the energy and momentum deposited by hard jet shower to soft medium. Our study demonstrates that the hydrodynamic medium response to jet propagation significantly enhances the broadening of jet shape at large angles and is essential for the cone-size dependence of jet energy loss and nuclear modification factor of inclusive jet production. It is also found that the nuclear modification pattern of jet shape is sensitive to jet energy but has weak dependence on the flavor of the parton that initiates the jet. Our result can naturally explain the different nuclear modification patterns of jet shape functions for single inclusive jet and $\gamma$-jet events as observed by the CMS Collaboration, and can be tested in the future by measuring the jet shape function over a wider range of jet energies in heavy-ion collisions.

Reference:
[1] Ning-Bo Chang, Guang-You Qin, Phys.Rev,C94,024902 (2016)
[2] Yasuki Tachibana, Ning-Bo Chang and Guang-You Qin, Phys.Rev,C95,044909 (2017)
[3] Ning-Bo Chang, Yasuki Tachibana and Guang-You Qin, Phys.Lett,B801,135181 (2020)

Speaker: Dr Ning-Bo Chang (Xinyang Normal University)

NingBo_Chang_Jet energy loss and jet shape modification.pdf

NingBo_Chang_Jet energy loss and jet shape modification.pptx

Recording

170 Jet substructure in p+p and p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV at STAR

In order to attribute the partonic energy loss within jets (jet quenching) observed in A+A collisions to the traversal of partons through the hot QCD medium, it is necessary to examine cold nuclear matter (CNM) effects on the corresponding jets. Such examination has historically been done using p+A collisions. In this talk, we present fully corrected measurements of jet substructure - with a focus on jet mass - in p+A collisions at STAR at $\sqrt{s_{\rm{NN}}}=200$ GeV as a function of the event activity (EA) to increase or decrease the magnitude of CNM effects. EA is determined in backward (Au-going) rapidity ($3.3<\left|\eta\right|<5.0$) by the STAR Beam-Beam Counter detector to minimize auto-correlation effects of jet measurements at mid-rapidity. By differentiating the measured jets by rapidity, we explore potential Bjorken-$x$ dependence in jets exiting the gold nucleus or proton. Finally, we compare the results in p+A collisions to fully corrected corresponding measurements in p+p collisions and current vacuum and heavy-ion Monte Carlo models to isolate these CNM effects in anticipation of an upcoming jet mass measurement in A+A collisions.

Speaker: Isaac Mooney

Mooney_HP20_final.pdf

Recording

Parallel: E2 - Electroweak Probes III

Convener: Peter Alan Steinberg (Brookhaven National Laboratory (US))

171 Non-UPC production of dimuons from two-photon scattering in Pb+Pb collisions with the ATLAS detector

Muon pairs produced via two-photon scattering processes in hadronic Pb+Pb collisions provide a potentially sensitive electromagnetic probe of the quark gluon plasma.
First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation between the two leptons and/or of the two-lepton $p_T$ distribution. ATLAS has recently measured dimuons produced via two-photon scattering in non-UPC Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$~TeV using an integrated luminosity of $1.9~\mathrm{nb}^{-1}$. This data set represents a factor of $\sim4$ increase in statistics over the 2015 data set used for the first ATLAS measurement. The increased statistics allow new features to be observed in the data, as well as differential studies of the dependence of the pair-distribution on the transverse-momentum and pseudorapidity of the two muons. The results of the new measurement and the possible physics implications will be discussed.

Speaker: Soumya Mohapatra (Columbia University (US))

2020-03-HP.pdf

Recording

172 Production of W/H+jets in Relativistic heavy-ion collisions

Gauge boson associated with jet production is a perfect channel for jet quenching. Z+jet and $\gamma+$jet correlations have already been investigated by several theory models and experimental groups in both p+p and Pb-Pb collisions at $\sqrt s=5.02$ TeV. However, W+jets are dominated by quark jet and H+jet are mainly gluon jet, the comparison of W+jet and H+jet would provide complementary information of jet quenching.

In the talk, we report a systematic calculation of W/H+jet production in Pb-Pb collisions at the LHC including jet quenching effects in the QGP. In the model, a nice baseline description of W+jet in p+p is achieved by utilizing Sherpa, a Monte Carlo event generator which combines the NLO with resummation by a matched parton shower (PS), and the parton energy loss in hot/dense QCD medium is simulated by Linear Boltzmann Transport(LBT) model.

We make predictions for the first time for the modifications of W/H+jet events due to jet-medium interactions: the modification of the distributions of events as a function of the vector sum of the lepton and jets $|\vec{p}_T^{Miss}|$, which is enhanced in small $|\vec{p}_T^{Miss}| $ region and suppressed in large $|\vec{p}_T^{Miss}|$ region due to jet energy loss in the opposite direction of the W boson. This observable can be easily observed in experimental and provide new information of jet quenching. While $|\vec{p}_T^{Miss}|$, is significantly broadened in PbPb collisions for H+jet event. Furthermore, we have investigated the shift of W/H+jet $p_T$ imbalance distribution $x_{jV}$, the suppression of jet yield per W/H trigger $R_{jV}$ and the modification of W/H+jet azimuthal angle correlations $\Delta \phi_{jV}$ as Z+jets, multi-jets have important contributions in small $\Delta \phi_{jV}$ and $x_{jV}$ phase space and the differences between W/H+jet and Z+jet will be discussed. We find that, H have much less jet partners and the tagged jet has smaller energy, but they loss the same fraction of its energy. What's more, we extended the Webber hadronization model to Pb+Pb collisions, with which we can make nice descriptions on the jet profile and jet fragmentation function both in p+p and Pb+Pb collisions.

Speaker: Mr Shan-Liang Zhang (Central China Normal University)

Recording

Shanliang_HP2020.pdf

173 The NA60+ experiment at the CERN SPS: physics goals and prospects

The region of the QCD phase diagram at high $\mu_{\rm B}$ can be accessed by fixed-target experiments working at future or existing facilities providing nuclear beams in the multi-GeV energy range. In particular, the CERN SPS is able to provide high-intensity beams over a wide energy interval ($\sqrt{s_{\rm NN}}$ = 5-17 GeV) that are ideal for the study of rare signals. Recently, an expression of interest has been presented for a new experiment at the CERN SPS, NA60+, aimed at measuring hard and electromagnetic probes in nuclear collisions with unprecedented precision with an energy scan.
The physics goals of such an experiment are very broad and ambitious. On one hand, NA60+ proposes the investigation of the order of the phase transition to the QGP in the region $\mu_{\rm B}\sim$ 200-400 MeV with the first measurement of a caloric curve, and the first direct measurement of $\rho-a_1$ chiral mixing by a precision measurement of the dimuon yield in the $a_1$ mass region. These physics topics can be addressed via the study of the thermal dimuon continuum from threshold up to 3 GeV. On the other hand, the study of the transport properties of the QGP close to the threshold energy for the occurrence of deconfinement can be accessed for the first time by a simultaneous precision study of hidden and open charm. The measurements of charmonium and open charm states are performed through dimuon and hadronic decays, respectively. In this talk, the physics case of the experiment will be reviewed with a detailed discussion of the results of the physics performance studies. The talk will stress the competitiveness and complementarity of the NA60+ program in the landscape of the proposals foreseen at other facilities in this decade.

Speaker: Enrico Scomparin (Universita e INFN Torino (IT))

HP2020_NA60plus_v4.pdf

Recording

174 Photon-Jet correlations in p-p and A-A collisions using the JETSCAPE framework

It is now well established that jet modification is a multistage effect; hence a single model alone cannot describe all facets of jet modification. The JETSCAPE framework is a multistage framework that uses several modules to simulate different stages of jet propagation through the QGP medium. These simulations require a set of parameters to ensure a smooth transition between stages. We fine tune these parameters to successfully describe a variety of observables, such as the nuclear modification factors of leading hadrons and jets, jet shape, and jet fragmentation function.

Photons can be produced in the hard scattering or as radiation from quarks inside jets. In this work, we study photon-jet transverse momentum imbalance and azimuthal correlation for both p-p and A-A collision systems. All the photons produced in each event, including the photons from hard scattering, radiation from the parton shower, and radiation from hadronization are considered with an isolation cut to directly compare with experimental data. The simulations are conducted using the same set of tuned parameters as used for the jet analysis. No new parameters are introduced or tuned. We demonstrate a significantly improved agreement with photons from A-A collisions compared to prior efforts. This work provides an independent, parameter free verification of the multistage evolution framework.

Speaker: Chathuranga Sirimanna (Wayne State University)

PhotonJetCorrelation_Chathuranga.pdf

Recording

175 Probing initial and final state effects with Z bosons in PbPb and Drell-Yan in pPb with the CMS detector

The differential yields of Z bosons decaying to lepton pairs are measured in PbPb collisions collected in 2018 by the CMS experiment at the LHC. The measurement uses 1.8 nb$^{-1}$ of 5.02~TeV data. The yields in various centrality bins are compared to the HG-PYTHIA model, which indicates that geometric and selection biases could be present for peripheral events. In some cases, the uncertainties of the measurement are smaller than the modeling uncertainties of the Glauber model, showing that Z-counting could be a preferred experimental measure of effective nucleon-nucleon luminosity. Additionally, a high precision measurement of the Z boson azimuthal anisotropy ($v_{2}$) is presented. This observable provides a second method to study whether Z bosons reconstructed in the leptonic decay channel experience significant final-state modifications. This is relevant for measurements in which a high-$p_{T}$ Z boson is used as a tag of a recoiling jet’s $p_{T}$. The final state modification of these jets is quantified by examining the $p_{T}$ imbalance of Z boson + jet pairs. A new measurement of the Drell-Yan (DY) process is also presented in pPb collision at the center of mass energy of 8.16 TeV with the CMS detector. The rapidity dependence of this process is particularly sensitive to nPDFs, but further information can be gained by studying the mass dependence of DY production, measured for the first time in pPb collisions at 8.16 TeV, down to 15 GeV. In addition, differential measurements in the dimuon $p_{\text{T}}$ or $\phi^{*}$ (an angular variable correlated with $p_{\text{T}}$ measured for the first time in pPb) provide insights on soft gluon emission at low $p_{\text{T}}$.

Speaker: Austin Alan Baty (Rice University (US))

Baty_ZBosons_HP2020_v5.pdf

Recording

Parallel: E3 - Heavy Flavor VII

Convener: joerg aichelin (Subatech/CNRS)

176 Charmed-baryon production and hadronization studies with ALICE

The measurements of the charmed baryons are fundamental to investigate charm-quark production and hadronization mechanisms in different collision systems.
Recent measurements of charm-baryon production in small systems at LHC energies show a baryon-over-meson ratio significantly higher than that in e$^{+}$e$^{-}$ and e$^{\pm}$p collisions, and higher than expectations from Monte Carlo generators, tuned to reproduce these measurements, suggesting a violation of the universality of the fragmentation of charm in different collision systems.
Various mechanisms are recently being considered in the theory community to describe the measurements, such as multi-parton interactions, colour reconnection, ropes, or statistical hadronization approaches.
In nucleus-nucleus collisions, where a hot and dense Quark-Gluon Plasma (QGP) forms and collectively expands, the enhancement of baryon-to-meson ratios is predicted by theoretical models in which heavy quarks hadronize by coalescence with light quarks from the plasma. Measurements of $\Lambda_{\rm c}$ production in nucleus-nucleus collisions hint to a larger ratio to D mesons, with respect to the case of pp collisions.
Furthermore, the measurement of open heavy flavours as a function of multiplicity in pp and p-Pb collisions provides important information to understand how the possible presence of collective effects could modify the production of heavy-flavour hadrons.
The analysis of different charm baryon species, such as $\Sigma_{\rm c}$ and $\Xi_{\rm c}$, give further insight into the study of the charm hadrons production in all systems.

In this talk, we present measurements of $\Lambda_{\rm c}$, $\Xi_{\rm c}$ and $\Sigma_{\rm c}$ baryons performed with the ALICE detector at mid-rapidity in pp collisions at various collision energies.
The $\Lambda_{\rm c}/ {\rm D}^{0}$ ratio measured in different collision systems and its multiplicity dependency from pp to p-Pb and Pb-Pb collisions will be shown. The $R_{\rm pPb}$ and the $R_{\rm AA}$ of the $\Lambda_{\rm c}$ will be discussed as well.
The results will be compared with predictions from Monte Carlo event generators in the pp system, and with models including CNM effects or the formation of a QGP in larger systems.

Speaker: Christopher Hills (University of Liverpool (GB))

HardProbes2020_CH_Final.pdf

Recording

177 Measurements of nuclear modification factors of $B_{S}^{0}$ and $B^{+}$ mesons in PbPb collisions with the CMS experiment

Beauty quarks are considered as one of the best probes of the strongly interacting medium created in relativistic heavy-ion collisions because they are predominantly produced via initial hard scatterings. Measurements of B meson production provide information about the diffusion of beauty quarks and the flavor dependence of in-medium energy loss. In these studies, clarifying the hadronization mechanism is crucial for understanding the transport properties of beauty quarks. Measurements of $B_{S}^{0}$ production can shed light on the mechanisms of beauty recombination in the medium and provide information about strangeness enhancement in the quark-gluon plasma. In this talk, we will present a new measurement of the ratio of $B_{S}^{0}$ to $B^{+}$ mesons in PbPb collisions at 5.02 TeV with the CMS detector, using data recorded in 2018.

Speaker: Zhaozhong Shi (Massachusetts Inst. of Technology (US))

Hard Probes 2020 Final Draft.pdf

Recording

178 Charmonia production with a density operator model

Quarkonia production in AA collisions has been the subject of vivid discussions since it was proposed as a signature of the quark-gluon plasma formed in these collisions. By now, it seems there is little doubt that both mechanisms of dynamical suppression and recombination are necessary in order to understand the most common observables, the nuclear modification factor RAA of J/Psi as well as its elliptic flow v2. On the level of models, there exist only a few which include these mechanisms and are able to address the comparison with experimental data. While some good agreement has been reached for the RAA, the explanation of the v2 remains problematic. Besides, some quantum features are still lacking proper implementation. From the theory side, a step in the direction of dealing with the formation of charmonia out of a large number of c and cbar quarks has been made recently [1] but still at the price of semi-classical approximations. Besides, to our knowledge, the numerical application to realistic AA collisions has not been achieved yet.

In our contribution, we present the application of a density operator model to charmonia production in AA collisions. The idea of the formalism goes back to the work of Remler, Gyulassy and Frankel [2,3] in which a general scheme connecting composite particle cross section with time-dependent density operators was derived from Von Neumann’s equation in the context of deuteron production. The formalism is indeed able to deal with the dynamical coalescence of many particles towards bound states. It inholds a unification of both the suppression and recombination processes, which is aguably an improvement of the existing models. We will present both the fundamental ingredients of the density operator formalism, its concrete implementation in EPOS-HQ and its application to RAA and v2 of J/psi at RHIC and LHC energies.

Bibliography
1. J-P Blaizot and M A Escobedo, JHEP 1806 (2018) 034
2. E.A. Remler, Annals of Physics 136 (1981) 293
3. M. Gyulassy and K. Frankel and E.A. Remler, Nuclear Physics A402 (1983) 596

Speaker: Pol Gossiaux (Subatech)

quarkonia density matrix gossiaux.pdf

Recording

179 DREENA framework as a multipurpose tool for QGP tomography

DREENA framework is based on our dynamical energy loss formalism, which takes into account finite size, finite temperature QCD medium consisting of dynamical (moving) partons. Both radiative and collisional energy losses are calculated under the same theoretical framework in the dynamical energy loss formalism, which is applicable to both light and heavy flavor observables. We generalized the formalism to the case of finite magnetic mass, running coupling,and towards removing widely used soft-gluon approximation. Importantly, DREENA provides a natural framework where temperature profile from any medium evolution can be straightforwardly implemented. We exploit this by implementing different state-of-the-art medium evolutions (both event-by-event hydrodynamics and kinetic transport theory) within DREENA framework.DREENA does not use free parameters, i.e. its only input is the temperature profile that comes directly from various hydrodynamics and kinetic theory models. This opens possibility to use DREENA on both light and heavy flavor to test and differentiate between different available QGP evolution models, including both large and smaller systems, making DREENA a multipurpose QGP tomography tool. Our results on these tests will be presented, which enables us to gain a better understanding of the bulk QGP medium created at RHIC and LHC. As a highlight, contrary to the existing models, which for full hydro evolution models lead to $v_2$ puzzle, with DREENA we surprisingly obtain a very good joint agreement between $R_{AA}$ and $v_2$ data.This well known puzzle therefore appears to be a consequence of a simplified energy loss commonly used by other models– once a proper description of parton medium interactions is used, $v_2$ puzzle is abolished. While a widely accepted paradigm is that proper medium evolution description dominates in explaining high pt data, this result strongly suggests that proper description of parton-medium interactions is much more important.

Speaker: Dusan Zigic (Institute of Physics Belgrade)

HP2020_DREENA_DZ.pdf

Recording

180 System size scan of D meson RAA and vn using PbPb, XeXe, ArAr, and OO collisions

Experimental measurements indicate no suppression (e.g. RpPb ∼ 1) but a surprisingly large D meson v2 was measured in pPb collisions. In order to understand these results we use Trento+v-USPhydro+DAB-MOD to make predictions and propose a system size scan at the LHC involving $^{208}PbPb$, $^{129}XeXe$, $^{40}ArAr$, and $^{16}OO$ collisions. We find that the nuclear modification factor approaches unity as the system size is decreased, but nonetheless, in the 0–10% most central collisions v2{2} is roughly equivalent regardless of system size. These results arise from a rather non-trivial interplay between the shrinking path length and the enhancement of eccentricities in small systems at high multiplicity. Finally, we also find a surprising sensitivity of D mesons v2{2} in 0–10% at pT = 2–5 GeV to the slight deformation of 129Xe recently found at LHC.

Speaker: Prof. Jacquelyn Noronha-Hostler (University of Illinois Urbana Champaign)

HP2020_NoronhaHostler.pdf

Recording

Parallel: E4 - Initial State V

Convener: Anthony Robert Timmins (University of Houston (US))

181 ATLAS measurements of transverse and longitudinal flow decorrelations in Xe+Xe, Pb+Pb, and $p$+Pb collisions

ATLAS measurements of flow harmonics ($v_n$) and their fluctuations in Pb+Pb and Xe+Xe collisions covering a wide range of transverse momenta, pseudorapidity and collision centrality are presented. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV, Pb+Pb collisions at 5.02 TeV, and $p$+Pb collisions at 5.02 and 8.16 TeV. The $v_{n}$ are measured up to $n=6$ using the two-particle correlations, multi-particle cumulants, and scalar product methods. The $v_{n}$ values are also performed using a non-flow subtraction technique that was developed for flow measurements in $pp$ and $p$+Pb collisions. This non-flow subtraction is found to have a significant effect on the measured $v_n$ at high-$p_T$ and in peripheral collisions. A universal scaling in the $p_{T}$ dependence of the $v_{n}$ is observed for both systems.
Measurements of correlations between the $v_n$ for different order $n$, studied with three- and four-particle mixed-harmonic cumulants, are also presented, and contributions to these correlations from ``centrality fluctuations'' are also discussed. Measurements of longitudinal flow decorrelations involving two- and four-particle correlations for $v_{2}$ and $v_{3}$ in Xe+Xe and $p$+Pb collisions are also presented and compared with the corresponding measurements in Pb+Pb collisions. The four-particle decorrelation is found to not factorize as a product of two-particle decorrelations. The ability of such measurements to distinguish between different models of initial geometry and to reduce the uncertainty in determining the effective shear-viscosity to entropy-density ratio of the QGP is demonstrated.

Speaker: Arabinda Behera (Stony Brook University (US))

HP20talk_ABehera_ver3.pdf

Recording

182 Chemical equilibration of QGP in hadronic collisions

We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma using the QCD effective kinetic theory in longitudinally expanding systems. We find that chemical equilibration takes place after hydrodynamization, but well before local thermalization. By relating the transport properties of QGP and the system size we estimate that hadronic collisions with final state multiplicities $dN_{ch}/dη≥10^2$ live long enough to reach approximate chemical equilibrium for all collision systems. Therefore we expect the saturation of strangeness enhancement to occur at the same multiplicity in proton-proton, proton-nucleus and nucleus-nucleus collisions.

References:
1. Aleksi Kurkela and Aleksas Mazeliauskas, Phys. Rev. Lett. 122, (2019) [arXiv:1811.03040],
2. Aleksi Kurkela and Aleksas Mazeliauskas, Phys. Rev. D99, (2019), [arXiv:1811.03068]

Speaker: Dr Aleksas Mazeliauskas (CERN)

mazeliauskas_HP.pdf

Recording

183 Kinetic and Chemical Equilibration of Quark-Gluon Plasma

We establish a non-equilibrium QCD evolution model with light quark and gluon degrees of freedom. By including both elastic and inelastic scattering for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of quark-gluon plasma, and thus connect the initial (semi-) hard production of partons at early times with the hydrodynamic description of a near-thermalized quark-gluon plasma after the first fm/c of collision. Within this approach, we investigate the time scales and mechanisms for kinetic and chemical equilibration of the quark-gluon plasma at zero and non-zero net-baryon density, and elaborate on the connections to jet quenching physics.

Speaker: Xiaojian Du (Universität Bielefeld)

HP2020QGP_xiaojiandu.pdf

Recording

184 Influence of the Multiplicity Fluctuations Distribution on Initial Conditions

One of the greatest uncertainties in heavy-ion collisions is the description of the initial state. Different models predict a wide range of initial energy density distributions based on their underlying assumptions. Final flow harmonics are sensitive to these differences in the initial state due to the nearly linear mapping between eccentricities and anisotropic flow harmonics. The Trento code uses a model-agnostic approach by phenomenologically parameterizing the initial state and constraining those parameters from a Bayesian analysis. In this framework, multiplicity fluctuations are determined by a one parameter gamma distribution. While this approach covers a broad class of initial-state models, it is not universal. Notably, initial-state models arising from the Color-Glass Condensate (CGC) framework lead to an initial energy density which is outside the functional form considered in Trento and its later Bayesian analyses. Instead, in the CGC approach the multiplicity fluctuations normally use a log-normal distribution. In this work we compare $T_{A}T_{B}$ scaling (CGC-like) to $\sqrt {T_{A}T_{B}}$ scaling (preferred from a Trento Bayesian analysis) and determine that the choice in a gamma distribution may inadvertently exclude $T_{A}T_{B}$ scaling from a Bayesian analysis.

Speaker: Patrick Carzon (University of Illinois at Urbana-Champaign)

Mult Fluct- Hard Probes.pdf

Recording

185 What attracts to attractors?What attracts to attractors?

Whether, how, and to what extent solutions of Bjorken-expanding systems become insensitive to aspects of their initial conditions is of importance for heavy-ion collisions. In this talk I will present attractor solutions in hydrodynamics, kinetic theory and holography, whereby we show that in hydrodynamics and kinetic theory the attractor extends to arbitrarily early times, whereas in holography the attractor solution is reached at the same timescale as the hydrodynamization timescale. Interestingly, in holography this can be intuitively understood by the presence of higher-order correlations, which are related to the initial conditions being present close to the black hole horizon in the dual gravitational theory.

Speaker: Wilke Van Der Schee (CERN)

Recording

WvdSchee_HP2020.pdf

12:10 Break

Parallel: F1 - Jets and High-PT Hadrons VII

P2

Convener: Helen Caines (Yale University (US))

186 Exploring large-R jets and substructure in Pb-Pb collisions at 5.02 TeV with ALICE

Due to recent advances in jet finding techniques and larger data samples, measurements of inclusive or recoil jets with large resolution parameters are now experimentally accessible via semi-inclusive hadron-jet or machine learning techniques, the latter of which enables the measurement of charged jet spectra down to low jet transverse momentum for jet resolution parameters up to $R=0.6$. By encompassing additional jet and medium response phase space, jet substructure measurements in these large R jets can provide further constraints on jet and medium properties. Of particular interest is the search for large transverse momentum kicks which may indicate the presence of point-like scatters within the QGP. We explore the jet substructure of inclusive and recoil jets in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV, utilizing Soft Drop and other grooming methods, as well as the Lund Plane, in order to access the hardest $k_{\mathrm{T}}$ splitting.

Speaker: Raymond Ehlers (Oak Ridge National Laboratory - (US))

2020-06-02.rehlers.hardest_kt_hard_probes_2020.v12.pdf

Recording

187 Jet suppression from small to large radius

The angular dependence of jet suppression encodes key information about the process of energy and momentum hydrodynamization, and for this reason can be used to greatly improve our understanding of fundamental aspects of the jet/QGP interaction. In this work we study jet suppression from small to very large radius, for low and very high energy jets at the LHC and RHIC. We use the hybrid strong/weak coupling model for jet quenching that combines perturbative shower evolution with an effective strongly coupled description of the energy and momentum transfer from the jet into the QGP. Because of momentum conservation, the wake created by the jet enhances or depletes the amount of particles generated at the freeze-out hypersurface depending on their orientation with respect to the jet. We find that jet suppression is surprisingly independent of the anti-$k_T$ radius R, first slightly increasing as one increases R, then at larger values of R very slowly decreasing [1]. This nearly independence of jet suppression with increasing values of R arises mainly from two competing effects, namely the larger energy loss of the hard jet components, which tends to increase suppression, versus the partial recovery of the lost energy due to medium response, reducing suppression. We also find that the boosted medium from the recoiling jet reduces the amount of plasma in the direction opposite to it in the transverse plane, increasing the amount of jet suppression due to an over-subtraction effect. We show that this characteristic signature of the hydrodynamization of part of the jet energy can be quantified by selecting samples of dijet configurations with different relative pseudorapidities between the leading and the subleading jet.

[1] D. Pablos, arXiv:1907.12301 - accepted by PRL

Speaker: Daniel Pablos (University of Bergen)

pablos_hp20.pdf

Recording

188 Constraints on jet quenching from a multi-stage energy-loss approach

A unified description of jet evolution through deconfined QCD matter remains one of the challenging problems in the area of heavy-ion physics. To gain a comprehensive understanding of the properties of the QGP, we need an energy-loss model that effectively captures the physics of multi-scale jet quenching and provides a simultaneous description of a wide variety of integrated and differential jet observables. In this talk, we present such a comprehensive study by performing a model-to-data comparison for leading hadrons, inclusive jets, and jet substructure observables. Within the JETSCAPE framework [1,2], an effective parton evolution is proposed which includes a high-virtuality, radiation dominated region followed by a low-virtuality, scattering dominated phase. Measurements of inclusive jet and single hadron $R_{AA}$ set strong constraints on the phase-space available for each stage of the energy-loss. The jet-medium response is incorporated through a weakly-coupled transport description with recoil particles excited from the QCD medium. This illustrates the central role played by recoil in the description of both integrated jet observables as well as the sub-structure of the jet. We also study cone size dependence of the nuclear modification factor for jets. This serves as an excellent probe to study the detailed mechanism of the lost jet energy inside the plasma.

[1] JETSCAPE Collaboration (J. H. Putschke (Wayne State U.) et al.), The JETSCAPE framework, arXiv:1903.07706 [nucl-th] (2019).
[2] JETSCAPE Collaboration (S. Cao (Wayne State U.) et al.), Multistage Monte-Carlo simulation of jet modification in a static medium, Phys. Rev. C96 (2017) no.2, 024909.

Speaker: Chanwook Park (McGill University)

Chanwook_Park_HP2020.pdf

Recording

189 An extraction of jet transport coefficient in cold nuclear matter from world data

Quantifying the nuclear modification due to multiple scatterings between jet and nuclear medium can provide a solid baseline for the identification of the medium fundamental property, which can be partly encoded in the nonperturbative jet transport coefficient ($\hat q$). In this work, we perform the first global extraction of the $\hat q$ for cold nuclear matter within the framework of the higher-twist expansion, which has been shown to be a successful approach to describe the nuclear effects observed in heavy ion collisions. The analysis takes into account the world data on the transverse momentum broadening in semi-inclusive eA deep inelastic scattering and in Drell-Yan dilepton and heavy quarkonium production in pA collisions, as well as the nuclear modification of the structure functions in DIS related to the coherent dynamical shadowing. The results of this work provide a quantitative evidence that the $\hat q$ for cold nuclear matter is a probing-scale dependent quantity similar to the standard parton distribution functions of proton, rather than a constant value usually used in heavy-ion study, which is expected to motivate a more precise understanding of the jet transport property of the quark-gluon plasma.

Speaker: Peng Ru (South China Normal University)

Recording

Ru_HP2020.pdf

190 Identification of Quenched Jets with Machine Learning

It is believed that the properties of quark-gluon plasma (QGP) can be studied through measurements of the jet quenching phenomenon. More specifically, detailed studies of the jet substructure may reveal the microscopic properties of the QGP.

Recently the modification of groomed jet observables was studied in heavy-ion collisions [1][2]. In addition, the Lund radiation plane was introduced to investigate parton shower modifications in the QGP [3].

In this talk, I am going to show how machine learning techniques can help evaluate how quenched a jet is on a jet-by-jet basis. A classifier based on the long short-term memory (LSTM) model is trained. The LSTM model is an artificial recursive neural network (RNN) and is capable of processing sequential data. This design makes it well-suited for making predictions on jets by taking advantage of the binary structure of parton branchings that form a jet.

Simulations are made with Monte-Carlo event generators including PYTHIA8, JEWEL and the hybrid strong/weak coupling model, the last two of which take the medium response into consideration.

Reference:
[1] Measurement of the splitting function in pp and PbPb collisions at √sNN =5.02TeV. arXiv:1708.09429.
[2] Exploration of jet substructure using iterative declustering in pp and Pb-Pb collisions at LHC energies. arXiv:1905.02512v1.
[3] Novel tools and observables for jet physics in heavy-ion collisions. arXiv: 1808.03689.

Speaker: Lihan Liu (Vanderbilt University (US))

hp2020_LihanLiu.pdf

Recording

Parallel: F2 - Jets and High-PT Hadrons VI

Convener: Abhijit Majumder (Wayne state university)

191 Jet charge modification in dense QCD matter

Jet production and jet substructure modification in heavy-ion collisions have played an essential role in revealing the in-medium evolution of parton showers and the determination of the properties of strongly-interacting matter under extreme conditions. It is imperative to extend these studies to include flavor tagging and to devise observables that are sensitive to the partonic origin of jets. The average jet charge, defined as the momentum-weighted sum of the electric charges of particles inside the jet, is a proxy of the electric charge of the quark or gluon that initiates the jet. We demonstrate how the factorization framework of soft-collinear effective theory can be generalized to evaluate the jet charge in a dense strongly-interacting matter environment, such as the one produced in nuclear reactions at collider energies. Observables that can separate the contribution of in-medium branching from the trivial isospin effects are identified and their connection to established jet quenching effects is elucidated. We present predictions for the transverse momentum dependence of the jet charge distribution in nucleus-nucleus collisions and its modification relative to the proton case.

Speaker: Dr Ivan Vitev

Recording

Vitev_HP2020.pdf

Vitev_HP2020.pdf

192 Microjet spectrum and intra-jet distributions in heavy-ion collisions

Jets in the vacuum correspond to multi-parton configurations that form predominantly via a branching process sensitive to the soft and collinear divergences of QCD. In heavy-ion collisions, energy loss processes, stimulated via interactions with the medium, affect jet observables in a profound way. On the level of Feynman diagrams this can be traced back to the difference of medium modifications imprinted in resolved and unresolved, including virtual, emissions along the cascade that is taking place inside and outside of the medium. This leads to a novel, non-linear resummation of jet energy loss through the so-called collimator function. In this talk we present new results on the combined effects of small-R resummation and energy loss to compute the R-dependent jet spectrum (called microjet spectrum) in heavy-ion collisions. We extend this analysis to the intra-jet distribution of inclusive hadrons and discuss the non-trivial role of factorization in this context. Finally, we set up a systematic inclusion of small-angle, medium-induced radiation and discuss its role on these observables.

Speaker: Konrad Tywoniuk (University of Bergen (NO))

HP2020_KonradTywoniuk.pdf

Recording

193 Measurements of groomed heavy-flavour jet substructure with ALICE

Recently, a variety of jet shape and substructure measurements in pp and Pb-Pb collisions have provided new insights into the processes of jet fragmentation and the mechanisms of jet interaction with the quark-gluon plasma. Grooming techniques, such as Soft Drop, allow us to access the hard splittings inside a jet by removing soft radiation emitted at large angles. These techniques provide a cleaner handle with which to explore the mechanisms of parton fragmentation both in the vacuum and in the presence of a hot QCD medium.

Thanks to the excellent tracking and particle identification of its detector, the ALICE collaboration is now capable of extending the study of jet substructure to the heavy-flavour sector by studying charm-tagged jets. Such measurements allow for the exploration of the mechanisms of parton fragmentation using a quark-enriched jet sample down to very low jet momenta and can therefore be used to identify differences between quark and gluon fragmentation as well as provide a reference for studying the flavour dependence of quark energy loss in Pb-Pb collisions.

In this talk, we show the first measurements of the groomed jet substructure variables, $z_g$ and $R_g$, using the Soft Drop algorithm for charged jets tagged by fully reconstructed D$^0$ mesons. Having access to the jet splittings involving fully reconstructed D$^0$ mesons also allows for the first direct measurement of the dead cone effect at colliders, by comparing the Lund plane of charm-tagged jets to that of inclusive jets. These results will be presented for pp collisions at $\sqrt{s}$ = 13 TeV and the prospects for similar measurements in Pb-Pb collisions will also be discussed.

Speaker: Vit Kucera (CERN)

D0_jet_substructure.pdf

Recording

194 Medium modification of jet substructure for inclusive, photon-tagged and heavy flavor jets in heavy-ion collisions

Recent measurements of jet substructure provide insights into how the hard and soft parts of the jets are modified by jet-medium interaction. One can also learn the flavor dependence of jet quenching via comparisons between boson tagged jet, inclusive jet and heavy flavor jet. In this study, with the Linear Boltzmann Transport (LBT) model, we investigate the jet shape, jet splitting function, and groomed jet mass in single jet, photon-jet and heavy flavor jet events. In order to identify the effect of jet induced medium response on jet substructure, we first fit the jet modification factor both with and without the medium response for a precise study.

Our study on jet shape function shows that the medium modifications for the core of quark jets and gluon jets are quite different and the broadening of jet profile at the edge of the jet cone is mainly carried by soft particles from medium recoil. We also find that the distributions of radiated gluon and recoiled parton are modified strongly by their rescatterings in the medium. The groomed jet study shows that jet induced medium response is responsible for the enhancement of large groomed mass tail while the jet-medium interaction generally leads to a smaller groomed mass of jets in heavy ion collisions. With different grooming setting, we explore the medium modification of different phase space to distinguish the contributions from medium induced radiation and medium recoil in gluon jet, quark jet and heavy flavor jet events. We further implement different scenarios of coherent and incoherent energy losses in LBT simulation and find that they have a significant impact on the pT dependence of the nuclear modification of jet splitting function.

Speaker: Tan Luo (IGFAE)

HP2020_TanLuo.pdf

Recording

195 Study of quenching of b-jets with the CMS experiment

Jet quenching is used to explore the detailed dynamics of QCD at high densities and temperature. In order to study the parton energy loss dependence on the flavor, we measure the b-jet nuclear modification factor with the latest recorded data-sets of pp and PbPb collisions at 5.02 TeV with CMS detector in 2017 and 2018. The higher center-of-mass energy, compared to the previous study at 2.76 TeV, allows us to access a larger range of b-jet transverse momentum. The use of the latest multi-variate b-tagging algorithms, as well as in-situ method to determine the b-jet efficiency and mistagging rate, dramatically reduce the uncertainties on the measurement. The result is unfolded to the particle level in order to facilitate the comparison to theoretical developments and other experiments. In addition to the nuclear modification to the b-jet spectra, the jet internal structure is studied via the jet shapes. We present the differential jet shape of b jets in pp collisions, as measured by the jet-track correlation method, and compare it to inclusive jet shapes and theoretical predictions.

Speaker: Xiao Wang (University of Illinois at Chicago (US))

Recording

Xiao_Hardprobe2020.pdf

Parallel: F3 - Heavy Flavor VIII

Convener: Deepa Thomas (University of Texas at Austin (US))

196 X(3872) production in pp with particle multiplicity

The last decade of hadron spectroscopy has unveiled a wealth of states that do not have the properties expected of particles composed of 2 or 3 valence quarks. Among the most intriguing of these exotics is the X(3872), which various models attempt to describe as a hadronic molecule, a compact tetraquark, an unexpected charmonium state, or their mixtures. Heavy ion collisions, as well as high multiplicity pp collisions, offer a new window on the properties of this poorly understood hadron. In these systems, promptly produced X(3872) hadrons can interact with other particles in the nucleus and/or those produced in the collision. The influence of these interactions on the observed X(3872) yields provides information that can help discriminate between the various models of its structure, as well as give insight into the dynamics of the bulk particles produced in these collisions. With a full range of precision vertexing, tracking, and particle ID capabilities covering 2 to 5 in units of rapidity, the LHCb experiment is especially well suited to measurements of both prompt and non-prompt exotic hadrons.
This talk will present new LHCb measurements X(3872) production in high multiplicity pp collisions through the decay to $J/\psi \pi^{+} \pi^{-}$.

Speaker: Cameron Dean (Los Alamos National Laboratory (US))

LHCb_X3872_HP2020_C_Dean.pdf

Recording

197 Evidence of X(3872) production in PbPb collisions with CMS experiment

The structure of the exotic meson $\chi_{c1}(3872)$, also known as $X(3872)$, is still under debate. The similarity of the $\chi_{c1}(3872)$ mass and the $D-\bar{D}^{*}$ mass threshold inspired the interpretation that $\chi_{c1}(3872)$ is a $D-\bar{D}^{*}$ “molecule” with small binding energy. Another explanation is that this meson is a tetra-quark, consisting of a di-quark and di-antiquark. Relativistic heavy-ion collisions produce an extremely hot and strongly interacting medium, which provides a new environment in which to study the nature of multi-quark states. Because of the dramatically different radii of a $D-\bar{D}^{*}$ “molecule” and a tetra-quark, the interactions of these two proposed states are expected to interact differently with the medium. Therefore, the yield of $\chi_{c1}(3872)$ in heavy-ion collisions can provide insight into its structure. The ratios of production cross-section of fully reconstructed $\chi_{c1}(3872)$ over $\psi(2S)$ in PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS detector are presented.

Speaker: Jing Wang (Massachusetts Inst. of Technology (US))

20200603_X3872_HP2020_JingWang_v7.pdf

Recording

198 Probing X(3872) structure via final state interactions

Recently, LHCb collaboration has presented the relative production rates of promptly produced X(3872) over ψ(2S) as a function of particle multiplicity, given by the total number of charged particle tracks reconstructed in the VELO detector for the forward pseudorapidity region, 2 < η < 5. This ratio is found to decrease with increasing multiplicity.

In fact, suppression of weakly-bound quarkonia states has been studied for decades in proton-nucleus collisions. Models incorporating final state effects, such as breakup via interactions with comoving hadrons, are able to describe the relative suppression of excited-over-ground quarkonium states in pA collisions.
In the case of proton-proton collisions, these final state effects can affect the quakonia production for multiplicities higher than the mean value, giving rise to a suppression that evolves with the increase of comoving particles.

We present our results for the ratio of X(3872) over ψ(2S) compared to LHCb data from proton-proton collisions. They are consistent with the interpretation of the X(3872) as being a tetraquark with a size between 1 to 2 fm and a biding energy of the order or smaller than the one of the ψ(2S). They disfavor the interpretation of the X(3872) as weakly bound hadronic molecule of large size.

We extend our study to PbPb collisions by the inclusion of recombination effects and compare our results to the available CMS data.

Speaker: Elena G. Ferreiro (Universidade de Santiago de Compostela (ES))

FerreiroHP2020b.pdf

Recording

199 X(3872) Transport in High-Energy Heavy-Ion Collisions

We investigate the in-medium kinetics of the X(3872) particle in ultrarelativistic heavy-ion collisions. Toward this end we employ our well-tested rate equation approach for charmonia to compute the time evolution of the X(3872) distribution with its two pertinent transport parameters, i.e., the equilibrium limit and inelastic reaction rate. The former is entirely determined by the X(3872)'s mass and the previously calculated charm-quark fugacity. The key new parameter is the reaction rate, believed to depend on the structure of the X(3872) particle ("large" for a DD* molecule and "small" for a diquark-antidiquark bound state). We evaluate the sensitivity of the final X(3872) abundance and pT spectra on different scenarios for its width and initial conditions. In particular, within the same transport approach, we obtain results for the X / Psi(2S) ratio as measured in experiment.

Speaker: Biaogang Wu

Recording

x_transport_HP2020.pdf

200 Study charm hadronization via $\Lambda_c$ and $D_s$ production in pp and PbPb collisions with the CMS experiment

Because of their large mass, the interactions of heavy quarks with the quark-gluon plasma (QGP) may be different from those of light quarks and hence can provide essential inputs in understanding the QGP. With strange quark yields being enhanced in the presence of a QGP, the production of $D_{s}^{+}$ is expected to be enhanced if recombination plays an important role in the hadronization process. Furthermore, studies of the lightest charm baryon, $\Lambda_{c}^{+}$, can provide further information to charm quark hadronization. Models involving quark coalescence predict a large enhancement of $\Lambda_{c}^{+}$ production in PbPb collisions compared to pp collisions. The $\Lambda_{c}^{+}$ and $D_{s}$ production in both pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been measured in the CMS experiment. Results of $\Lambda_{c}^{+}$ and $D_{s}$ differential cross-sections, and the ratios of these two yields over those for $D^{0}$ in pp and PbPb collisions, as well as $R_{AA}$ for $D_{s} $ and $\Lambda_{c}^{+}$, are presented.

Speaker: Milan Stojanovic (Purdue University (US))

MStojanovic_HP2020_v2.pdf

Recording

Parallel: F4 - New Theoretical Developments I

Convener: Raju Venugopalan (Brookhaven National Laboratory)

201 Entanglement, partial set of measurements, and diagonality of the density matrix in the parton model

We consider the following conundrum: On one hand the proton as a quantum object is in a pure state and is described by a completely coherent wave function with zero entropy. On the other hand in high energy experiments (DIS) when probed by a small external probe, it behaves like an incoherent ensemble of (quasi-free)
partons.

In this talk, we define the "entropy of ignorance" which quantifies the entropy associated with ability to perform only a partial set of measurement on a quantum system. For a parton model the entropy of ignorance is equal to a Boltzmann entropy of a classical system of partons. We analyze a calculable model used for describing low x gluons in Color Glass Condensate approach, which has similarities with the parton model of QCD. In this model we calculate the entropy of ignorance in the particle number basis as well as the entanglement entropy of the observable degrees of freedom. We find that the two are similar at high momenta, but differ by a factor of order unity at low momenta. This holds for the Renyi as well as von Neumann entropies. We conclude that the entanglement does not seem to play an important role in the context of the parton model.

Speaker: Dr Vladimir Skokov (North Carolina State University)

HP2020.pdf

Recording

202 The problem of overlapping formation times: A complete result for QCD

The splitting processes of bremsstrahlung and pair-production in a medium are coherent over large distances in the high energy limit leading to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. Avoiding soft-emission approximations and working in the large-Nc limit, we consider corrections to the LPM effect from cases where the coherence lengths of two consecutive splittings overlap. In this work, we present (i) complete results for the case of two overlapping gluon splittings (e.g. $g\rightarrow gg\rightarrow ggg$ and virtual corrections to single splitting $g\rightarrow gg^{*}\rightarrow ggg^{*}\rightarrow gg$) and (ii) confirm that earlier leading-log results for these effects are reproduced by our more-complete results in the appropriate soft limit. We also discuss how to combine the effects of overlapping real double splitting with the corresponding virtual corrections to single splitting in order to calculate IR-safe quantities such as in-medium energy loss.

Speaker: Dr Shahin Iqbal (Institute of Particle Physics, Central China Normal University)

Recording

Shahin_HP2020.pdf

203 On gauge invariance of transverse momentum dependent distributions at small x

The interplay between the small x limit of QCD amplitudes and QCD factorization at moderate x has been studied extensively in recent years. It was finally shown that semiclassical formulations of small x physics can have the form of an infinite twist framework involving Transverse Momentum Dependent (TMD) distributions in the eikonal limit. In this work, we demonstrate that small x distributions can be formulated in terms of transverse gauge links. This allows in particular for direct and efficient decompositions of observables into subamplitudes involving gauge invariant suboperators which span parton distributions. The application to Dijet production in eA collisions will be discussed beyond the correlation limit as well as a strategy to compute finite energy corrections.

Speaker: Dr Yacine Mehtar-Tani (Brookhaven National Laboratory)

HP2020-mehtar.pdf

Recording

204 QCD Correlations in Multiple Gluon Bremsstrahlung

We compute for the first time the spectrum for emitting 1, 2, and 3 soft and collinear gluons from a hard scattering process in full QCD. This result is important because 1) all current energy loss calculations assume QED-like independent emissions of multiple gluons, which obviously misses all correlations from the non-Abelian nature of QCD, and 2) the average high-p$_{\mathrm{T}}$ parton emits ~3 gluons as it escapes the medium. QCD correlations are therefore critical for any realistic comparison of theoretical predictions to experimental data on jets and jet substructures in heavy ion collisions. These calculations additionally provide a benchmark for jet Monte Carlo algorithms. As part of the talk, we will give a brief overview of the spinor helicity formalism, sometimes referred to as a twistor expansion or the use of maximal helicity violating (MHV) techniques, which provide the massive simplifications necessary for performing the novel derivations.

Speaker: William Alexander Horowitz (University of Cape Town (ZA))

200603(HP)Horowitz.pptx

Recording

205 Revisiting heavy quark radiative energy loss in nuclei with in the high-twist approach

We revisit the calculation of multiple parton scattering of a heavy quark in nuclei within the framework of recently improved high-twist factorization formalism, in which gauge invariance is ensured by a delicate setup of the initial partons’ transverse momenta. We derive a new result for the heavy quark radiative energy loss in deeply inelastic scattering. By taking the massless limit, it is consistent with the previous calculation of light quark energy loss. But in the heavy quark case, it leads to a new correction term, which vanishes in the soft gluon radiation limit. We show numerically the significance of the new correction term in the calculation of heavy quark energy loss as compared to previous studies and with soft gluon radiation approximation.

Speaker: Dr Yilun Du (University of Bergen)

HP2020_Yilun_Du.pdf

Recording

Thursday 4 June

Plenary: Heavy Flavor I

Plenary

Convener: Ralf Rapp (Texas A&M University)

206 Lattice and Effective Field Theories for Hard Probes

Speaker: Nora brambilla

hardprobes2020.pdf

Recording

207 Open Heavy Flavor: Theory

Speaker: Vincenzo Greco (University of Catania)

Greco-HF-Theory-HP2020-v.pdf

Recording

208 Open Heavy Flavor: Experiment

Speaker: Camelia Mironov (Massachusetts Inst. of Technology (US))

hp20_hfExp_20200604_mironov_v2.pdf

09:15 Break

Plenary: Heavy Flavor II

Plenary

Convener: Ramona Vogt (LLNL)

209 Quarkonia: Theory

Speaker: Yan-Qing Ma

Recording

YQMa20200604.pdf

210 Quarkonia: Experiment

Speaker: John Matthew Durham (Los Alamos National Laboratory)

Durham_HardProbes2020.pdf

Recording

10:20 Lunch

Parallel: G1 - Jets and High-PT Hadrons IX

P2

Convener: Christine Nattrass (University of Tennessee (US))

211 Search for jet quenching effects in high-multiplicity proton-proton collisions at 13 TeV with ALICE

Jet quenching is a possible consequence of the formation of a quark-gluon plasma (QGP) in collision systems, but to date no significant jet quenching has been observed in small systems. In this talk, the ALICE Collaboration reports results of a novel approach to jet-quenching measurements in high-multiplicity pp collisions at √𝑠=13 TeV, searching for the broadening of the acoplanarity distribution measured by the semi-inclusive distribution of jets recoiling from a high-pT hadron. Charged-jet reconstruction is carried out using the anti-kT algorithm with R=0.4 and a data-driven statistical method is used to correct the measured jet yield for uncorrelated background, which includes multi-partonic interactions. High-multiplicity (HM) pp events are selected based on charged-particle multiplicity registered in forward scintillator detectors and their acoplanarity distributions are compared to that for Minimum Bias (MB) events. Significant broadening is observed in the acoplanarity distribution of HM events, consistent with jet quenching. However, qualitatively similar features are also seen in pp collisions generated by the PYTHIA which does not include the simulation of jet quenching or any other QGP effects. We will discuss the current status of this analysis, and prospects to understand the origin of this striking phenomenon.

Speaker: Filip Krizek (Czech Academy of Sciences (CZ))

Recording

slides_HP_v8.pdf

212 First Results from Hybrid Hadronization in Small and Large Systems

“Hybrid Hadronization” is a new Monte Carlo package to hadronize systems of partons. It smoothly combines quark recombination applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems, following the picture outlined by Han et al. [PRC 93, 045207 (2016)]. Hybrid Hadronization integrates with PYTHIA 8 and can be applied to a variety of systems from $e^++e^-$ to A+A collisions. It takes systems of partons and their color flow information, for example from a Monte Carlo parton shower generator, as input. In addition, if for A+A collisions a thermal background medium is provided, the package allows to sample thermal partons that contribute to hadronization. Hybrid Hadronization is available for use as a standalone code and is also part of the JETSCAPE 2.0 release.
In this presentation we review the physics concepts underlying Hybrid Hadronization and demonstrate how users can use the code with various parton shower Monte Carlos. We present calculations of multiplicities, hadron chemistry, fragmentation functions and jet shapes in $e^++e^-$, $p+p$ and A+A collisions when Hybrid Hadronization is combined with different parton shower Monte Carlos (PYTHIA 6, PYTHIA 8 and JETSCAPE/MATTER). We compare to calculations using pure Lund string fragmentation as well as to data from LEP, RHIC and LHC. In particular, we discuss observable effects of the recombination of shower partons with thermal partons.

Speaker: Michael Kordell (Wayne State University)

HybridHadronization.pdf

HybridHadronization.pptx

Recording

213 Medium response from mini-jets and in-medium hadronization in relativistic heavy ion collisions

In ultra-relativistic heavy-ion collisions, partons with intermediate energy (5-10) GeV excite ripples as they travel through the Quark-Gluon Plasma (QGP).
These ripples' effect on particle production phenomenology is not very well studied.
In this work, we extend our previous work \cite{Ryu:2018ckh} and present study using a state-of-the-art hybrid framework that consists of the IP-Glasma pre-thermalization dynamics, viscous hydrodynamics (MUSIC), jet energy loss (MARTINI), and hadronic re-scatterings (UrQMD). This framework consistently handles both soft and hard physics involved in relativistic heavy ion collisions.
We consider the energy loss of mini-jets, whose energy is between 5 to 10 GeV, and their induced medium excitation.
The energy and momentum lost from the mini-jets are treated as either free-streaming wave-packets or causal diffusive perturbations of the hydrodynamic flow.
They alter the energy-stress tensor evaluated on the particlization hypersurface during the hadronization as jet induced medium response.
In addition, this approach uses a novel in-medium fragmentation where the color neutrality of a string is enforced locally.
We quantify the importance of the medium response from mini-jets propagation and their in-medium hadronization on identified particle $p_T$-spectra and their flow anisotropic coefficients.

S. Ryu, S. McDonald, C. Shen, S. Jeon and C. Gale,
``Effects of hadronic rescattering in mini-jet production and energy loss at the LHC''
PoS High-pT 2017, 014 (2019).
doi:10.22323/1.320.0014

Speaker: Dr Sangwook Ryu (Wayne State University)

Recording

slide_HP2020_SRyu.key

slide_HP2020_SRyu.pdf

214 Resolving the spacetime structure of jets with medium

Away from the strictly soft and collinear limit of QCD radiation the choice of evolution scale in a parton shower algorithm is ambiguous and several options have been implemented in existing Monte Carlo event generators for proton-proton collisions [1]. However, the resulting space-time evolution could result in subtle differences depending on the particular choice. In this work we quantify measurable consequences of the choice of the evolution variable and show how the implications of such a choice propagates into jet quenching observables. We develop a parton shower algorithm for a general evolution variable, that includes as special cases the virtuality, angle, transverse momentum and formation time. We study the interplay between the shower history for different evolution variables and the phase space affected by parton energy loss. In particular, we implement effects of jet quenching in the dense and dilute medium limits and highlight the role of color coherence effects [2,3]. We compare the results of the different ordering variables to existing Monte Carlo shower implementations on the parton level by analyzing primary and secondary Lund planes. Finally, we study the sensitivity of quenched jets to the choice of evolution variable by confronting our results for certain key observables, such as the inclusive jet spectrum, the (groomed) momentum sharing fraction or the jet mass, against theoretical expectations and experimental data.

References
[1] T. Sjostrand, Status and developments of event generators,PoS LHCP2016, 007 (2016).
[2] J. Casalderrey-Solana, D. Pablos and K. Tywoniuk, Two-gluon emission and interference in athin QCD medium: insights into jet formation, JHEP1611, 174 (2016).
[3] Y. Mehtar-Tani and K. Tywoniuk, Sudakov suppression of jets in QCD media, Phys. Rev. D98, no. 5, 051501 (2018).

Speaker: Adam Takacs (University of Bergen)

Adam_Takacs_HardProbes_2020_short.pdf

Recording

215 Parton modification studies using electroweak-boson-tagged hadrons with pp and PbPb collisions at 5.02 TeV with the CMS experiment

Electroweak bosons can be used to constrain the kinematics, as well as the flavor, of the recoiling parton, before its interaction with the quark-gluon plasma. While photons are more abundant, they suffer from larger systematic uncertainties, particularly at low transverse momentum ($p_\mathrm{T}$), from the background photons from neutral meson decays. Tagging with Z bosons is a complementary way to study modifications of low $p_\mathrm{T}$ partons as well as the soft particles from the medium response. The talk will present studies of kinematics correlations between electoweak bosons and charged particles in pp and PbPb collisions at $\sqrt{s_\mathrm{NN}} = 5.02\,\mathrm{TeV}$ using data collected with the CMS detector.

Speaker: Kaya Tatar (Massachusetts Inst. of Technology (US))

200604_HP2020_KayaTatar.pdf

Parallel: G2 - Jets and High-PT Hadrons VIII

Convener: Urs Wiedemann (CERN)

216 Jet quenching in the hadron gas: an exploratory study

The suppression of high momentum particles in heavy-ion collisions in comparison to elementary reactions is one of the main indications for the formation of a quark-gluon plasma. In recent studies, full jets are being reconstructed and substructure observables are gaining importance in assessing the medium modifications of hard probes. In this work, the effect of the late stage hadronic interactions are explored within the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons)[1]. High momentum particles are incorporated in a radially expanding hadron gas to analyse the corresponding angular distributions, also referred to as ‘jet shape’ observables. We find that the full hadron gas can be approximated with a pion gas with constant elastic cross-sections of 100 mb. In addition, the temperature and probe energy dependence of diffusion coefficients $\tilde{q}$ and $\tilde{e}$ quantifying the transverse and parallel momentum transfers are extracted. The species dependence and the importance of different interaction types are investigated. Parametrizations are presented that can be employed in future jet quenching calculations to include the effect of the hadronic phase.

[1] P. Dorau, J.-B. Rose, D. Pablos and H. Elfner, arxiv:1910.07027

Speaker: Hannah Elfner

Elfner_HP2020.pdf

Recording

217 Jets and medium evolution in Pb-Pb collisions at the LHC energies from the EPOS initial state

We present the results for PbPb collisions at 2.76 TeV LHC energy from a parton shower integrated with a hydrodynamic evolution. The initial hard (jet) partons are produced along with soft partons in the initial state EPOS approach (EPOS3 model). The EPOS3 initial state typically contains multiple hard scatterings in each event. The soft partons, represented by strings, melt into a thermalized medium which is described with a 3 dimensional event-by-event viscous hydrodynamic approach. The jet partons then propagate in the hydrodynamically expanding medium. The total jet energy gets progressively “degraded” according to a state-of-the-art microscopic radiative energy loss Monte Carlo for the low-virtuality jet partons. Also, partons reaching a certain lower cut off are “melted” into the hydrodynamic medium via the source terms. The full evolution proceeds in a concurrent mode, without separating hydrodynamic and jet parts. We discuss two features of PbPb collision:
- a jet overlap effect [1] which emerges due to multiple hard parton production in each heavy-ion collision event,
- jet energy loss in the medium and its modification due to the LPM effect.

[1] Iurii Karpenko, Joerg Aichelin, Pol Gossiaux, Martin Rohrmoser, and Klaus Werner, Phys. Rev. C 101, 014905 (arXiv:1908.00836)

Speaker: Dr Iurii Karpenko (FNSPE CTU Prague)

HP2020-karpenko.pdf

Recording

218 Light meson nuclear modification factor in p-Pb collisions over an unprecedented transverse momentum range with ALICE

Light meson measurements in high-energy proton-nucleus collisions provide a probe to study the physics of strongly interacting matter and the quark-gluon plasma (QGP). In particular, measuring the nuclear modification factor $R_{pA}$, where the particle production in pA is compared to a baseline proton-proton reference which is scaled to account for nuclear geometry, provides important insights to the modfication of nucleon structure functions in nuclei and a baseline for the observed strong suppression of hadron yields at high $p_{\rm T}$ in heavy-ion collisions.

In this talk, neutral pion and $\eta$ meson invariant differential yields and nuclear modification factors at midrapidity are presented with a $p_{\rm T}$ reach beyond 100 GeV/$c$ and up to $40$ GeV/$c$, respectively, and compared to theoretical model calculations. Both neutral mesons are measured via their diphoton decay channel in pp and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 and 8.16 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from several partially independent reconstruction techniques where the decay photons were detected with the electromagnetic calorimeter, EMCal, the photon spectrometer, PHOS, or via reconstruction of $e^+e^-$ pairs from conversions in the ALICE detector material using the central tracking system.

Speaker: Nicolas Schmidt (ORNL)

2020_06_Hard_Probes_highpT.pdf

Recording

219 PHENIX results on nuclear modification of hadron production in small and large systems

The intermediate pT region is ideal for studying hadronization and the
transition from soft to hard physics.  Quark mass and flavor are key
ingredients in hadronization as well as elucidating the details of energy
loss mechanisms in the hard sector.  For this reason, it is essential to
study a variety of different particle species, and PHENIX is ideally-suited
for many resonance decay analyses.  In this talk we present spectra and
nuclear modification factors of identified particles $\pi^0$, $\omega$,
$K_S$, $K^*$, and $\phi$ in p+Al, p+Au, d+Au, 3He+Au, Cu+Au, Au+Au, and U+U
collisions.  Implications for hadronization and energy loss will be
discussed.

Speaker: Axel Drees

Drees_HP2020.pdf

Recording

220 How many observables are necessary to constrain light parton transport properties?

Interactions between hard partons and the quark-gluon plasma range from frequent soft interactions to rare hard interactions. While it is reasonable that hard interactions can be described perturbatively, soft interactions likely suffer from significant non-perturbative effects. Since the effect of the soft interactions can be encoded into parton transport coefficients, these non-perturbative effects can in principle be quantified by extracting the drag and diffusion of light partons from heavy ion measurements.

In this work, we perform a proof of principle calculation to determine to what extent the drag and diffusion of light partons can be constrained from jet measurements. We implement this study in the JETSCAPE framework [1] using a hard-soft factorized parton energy loss model derived in the weakly-coupled limit [2]. We first calculate a set of jet observables using known drag and diffusion coefficients. By then applying a Bayesian analysis on these observables, we determine which observables can best constrain the light parton transport coefficients. We use this closures test to understand how adding observables, or reducing uncertainties on specific observables, can improve constraints on the parton's transport coefficients.

---

[1] Putschke, J. H., Kauder, K., Khalaj, E., Angerami, A., Bass, S. A., Cao, S., ... & Elfner, H. (2019). The JETSCAPE framework. arXiv preprint arXiv:1903.07706.
[2] Ghiglieri, J., Moore, G. D., & Teaney, D. (2016). Jet-medium interactions at NLO in a weakly-coupled quark-gluon plasma. Journal of High Energy Physics, 2016(3), 95.

Speaker: Tianyu Dai (Duke University)

Recording

Tequila_HP20.pdf

Parallel: G3 - Heavy Flavor IX

Convener: William Alexander Horowitz (University of Cape Town (ZA))

221 Production and azimuthal anisotropy of muons from heavy flavor decays in small and large systems with ATLAS

Heavy flavor production and collectivity in A+A collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in the QGP medium. In this talk, ATLAS measurements on nuclear modification factor and $v_{2}$ and $v_{3}$ flow coefficients of muons from heavy flavor decays in Pb+Pb collisions are presented as a function of muon $p_{T}$ and centralities. Muons with charm and bottom origins are separated based on the transverse impact parameter with respect to the primary collision vertex. To better understand the origin of collectivity in small systems, azimuthal anisotropy of muons from heavy flavor decays is also measured in $p$+Pb and $pp$ collisions. A template fit method is used in small system to subtract non-flow contributions using simultaneous fit to low and high charged-particle multiplicity samples. The extracted $v_{2}$ coefficients are presented as a function of muon $p_{T}$ and event charged-particle multiplicity.

Speaker: Qipeng Hu (University of Colorado Boulder (US))

ATLAS_HF_HP2020_QipengHu.pdf

Recording

222 Open charm and dileptons from relativistic heavy-ion collisions

Dileptons are considered as one of the cleanest signals of the quark-gluon plasma (QGP),however, the QGP radiation is masked by many 'background' sources from either hadronic decays or semileptonic decays from correlated charm pairs. In this study we investigate the relative contribution of these channels in heavy-ion collisions from $\sqrt{s_{\rm NN}}=$ 8 GeV to 5 TeV with a focus on the competition between the thermal QGP radiation and the semileptonic decays from correlated $D-$meson pairs. As a 'tool' we employ the parton-hadron-string dynamics (PHSD) transport approach to study dilepton spectra in Pb+Pb (Au+Au) collisions in a wide energy range incorporating for the first time a fully microscopic treatment of the charm dynamics and their semileptonic decays. We find that the dileptons from correlated $D-$meson decays dominate the 'thermal' radiation from the QGP in central Pb+Pb collisions at the intermediate masses (1.2 GeV $< M <$ 3 GeV) for $\sqrt{s_{NN}} > $ 40 GeV, while for $\sqrt{s_{\rm NN}}=$ 8 to 20 GeV the contribution from $D,{\bar D}$ decays to the intermediate mass dilepton spectra is subleading such that one should observe a rather clear signal from the QGP radiation. We, furthermore, study the $p_T$-spectra and the $R_{AA}(p_T)$ of single electrons at different energies as well as the excitation function of the inverse slope of the $m_T$- spectra for intermediate-mass dileptons from the QGP and from charm decays. We find moderate but characteristic changes in the inverse slope parameter for $\sqrt{s_{NN}} > $ 20 GeV which can be observed experimentally in high statistics data. Additionally, we provide detailed predictions for dilepton spectra from Pb+Pb collisions at $\sqrt{s_{NN}} = $ 5.02 TeV.

Speaker: Elena Bratkovskaya (GSI, Darmstadt)

Bratkovskaya-HP-2020.pdf

Recording

223 Elliptic flow of electrons from heavy-flavor decays in 54.4 and 27 GeV Au+Au collisions from the STAR experiment at RHIC

Measurements of heavy-flavor hadron production and elliptic flow ($v_{2}$) provide unique and indispensable information for understanding the properties of the quark-gluon plasma. Recent STAR measurements indicate that in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=$ 200 GeV $D^{0}$ mesons develop large $v_{2}$ similarly as light-favor hadrons, implying that charm quarks interact strongly with the thermalized medium at the top RHIC energy. Interestingly, at lower collision energies the electrons from heavy-flavor decays seem to exhibit much lower $v_{2}$, unlike the light-flavor hadrons. However, the precision of the previous results from STAR at $\sqrt{s_{\mathrm{NN}}}$ = 62.4 and 39 GeV did not allow for firm conclusions.

Thanks to the large data samples recorded by STAR in 2017 and 2018, we are now able to perform more precise measurements of the $v_{2}$ of electrons from heavy-flavor decays in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}= 54.4$ and $27$ GeV. The collected data sample at $\sqrt{s_{\mathrm{NN}}}$ = 54.4 GeV and 27 GeV are more than 10 times larger than those at $\sqrt{s_{\mathrm{NN}}}$ = 62.4 and 39 GeV respectively, used in the previous STAR analysis. In this talk, we will present the new results from the STAR experiment on the $v_{2}$ of electrons from heavy-flavor decays, at $\sqrt{s_{\mathrm{NN}}}$ = 54.4 and 27 GeV, as a function of electron transverse momentum. We will also discuss physics implications of these results by comparing to theoretical model calculations.

Speaker: Ms Yuanjing Ji (University of Science and Technology of China)

hardprobe_npe_v14.pdf

NPEv2_yj.mp4

Recording

224 Measurements of electron production from heavy flavor decays in p+p and Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV with the STAR experiment

Heavy quarks are predominantly produced at the early stages of relativistic heavy-ion collisions before the formation of the quark-gluon plasma (QGP) medium. Heavy quarks subsequently traverse the QGP throughout its whole evolution, and thus are suggested as excellent probes to study the properties of the QGP. Theory predicts heavy quarks lose less energy than light quarks through gluon radiation. Measurements of the production of electrons from open heavy flavor hadron decays (Heavy Flavor decayed Electron, HFE), in p+p and Au+Au collisions and the nuclear modification factor, $R_{AA}$, of HFE provide valuable tool to understand the interactions of heavy quarks with the QGP medium. Furthermore, measurements of the HFE $R_{AA}$ can be combined with separate measurements of the open bottom decayed electron fraction in HFE to evaluate the $R_{AA}$ of open bottom decayed and open charm decayed electrons and investigate the mass hierarchy of parton energy loss in the QGP.

In this talk, we will present the new results of HFE production in p+p collisions at $\sqrt{s}$ = 200 GeV from the STAR experiment with significantly improved precision compared to the previous measurements. We will also report measurements of the nuclear modification factor, $R_{AA}$, for HFE production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.

Speaker: Yingjie Zhou (Central China Normal University CCNU (CN))

Recording

Yingjie_HP20_final.pdf

225 A comprehensive description of open-heavy flavour observables in heavy-ion collisions within a transport approach

We present recent developments of the POWLANG transport model for the study of heavy-flavour (HF) production in heavy-ion collisions. In particular we focus on the results of recent/ongoing work concerning:

1. Event-shape engineering studies of D-meson distributions;

2. Full 3+1 transport simulations validated against soft-particle production data. The realistic 3+1 hydrodynamic background allows us to study the HF directed flow v_1 and the HF decay muons at forward rapidity, so far neglected in most theoretical calculations. ;

3. Medium-induced changes in the HF hadronization, accounting for 4-momentum conservation, space-momentum correlations and modification in the HF-hadrochemistry, this motivated by the experimental data on the production of D_s meson and Lambda_c baryons.

Speaker: Andrea Beraudo (INFN, sezione di Torino (IT))

beraudo-HP.pdf

Recording

Parallel: G4 - New Experimental Developments

Convener: Harald Appelshaeuser (Goethe University Frankfurt (DE))

226 Heavy flavor and jet studies for the future Electron Ion Collider

The proposed high luminosity high energy Electron Ion Collider (EIC) will explore the proton/nuclear structure, search for gluon saturation and precisely determine the nuclear parton distribution functions (nPDFs) in a wide x-$Q^{2}$ phase space. Heavy flavor and jet measurements at the future EIC will allow us to better constrain the nPDFs within the poorly constrained high Bjorken-x region, precisely determine the quark/gluon fragmentation processes and directly study the quark/gluon energy loss within the nuclear medium. We propose to develop a new physics program to study the flavor tagged hadrons/jets, heavy flavor hadron-jet correlations and flavor dependent jet fragmentation processes in the nucleon/nucleus going direction (forward region) at the EIC. These proposed measurements will provide a unique path to explore the flavor dependent fragmentation functions and energy loss in heavy nuclei, which can constrain the initial state effects for previous and ongoing heavy ion measurements at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). A forward (proton/nuclei going direction) silicon tracking detector is essential to carry out these measurements at the EIC. In addition to the EIC heavy flavor and jet physics developments, the forward silicon tracking detector R$\&$D and detector design are ongoing with the Los Alamos National Laboratory Lab Directed Research and Developments (LDRD) supports. Details of the proposed new physics program, progresses of the detector and physics simulation studies and the status of the detector R$\&$D will be discussed in this presentation.

Speaker: Xuan Li (Los Alamos National Laboratory)

HP2020_XuanLi_v3.pdf

Recording

227 LHC Run 3 and Run 4 prospects for heavy-ion physics with LHCb

The largely unknown parton distribution functions of nuclei and the similarities observed between high-multiplicity pp and pPb events compared to PbPb, often described by means of hydrodynamics, are the main motivations for an extended pPb data taking program during LHC Run 3 and Run 4.
The future increase in luminosity combined with the LHCb unique and improved detector capabilities in the upgrade will allow to perform new and precise measurements.
Moreover, an upgraded internal gas target is going to be installed for the LHCb run 3 fixed target program, allowing a wider choice of target gas species and an increase of the gas density by up to two order of magnitude.
Prospects will be presented on both the LHCb collider and fixed target programs.

Speaker: Samuel Belin (Universita e INFN, Cagliari (IT))

hardprobes_2020_belin_v2.pdf

Recording

228 Prospects for new measurements using advanced silicon technologies in ALICE

A Large Ion Collider Experiment plans intensive use of silicon technologies for extensions of the experiment, beyond the currently ongoing upgrade during the Long Shutdown 2 of the LHC. For Run 4, we will discuss the plans for the installation of three new layers of the Inner Tracking system, based on wafer-sized sensors sufficiently thinned to be rolled to a cylinder. This will lead to an unprecedentedly low material budget, and consequently drastically reduced interaction probabilities and unparalleled vertexing performance. For Run 5 and beyond, we will present ideas for a next-generation heavy-ion experiment fully based on silicon sensors for tracking, time-of-flight and shower measurements. This combines the advantages of extremely low material budget, fast read-out and high resolution.

Speaker: Marco Van Leeuwen (Nikhef National institute for subatomic physics (NL))

20200603_HP_SiliconTechnologies_MvanLeeuwen.pdf

Recording

229 New opportunities in heavy ion physics at HL-LHC with a MIP Timing Detector at the CMS experiment

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). A new timing layer is designed to measure minimum ionizing particles (MIPs) with a time resolution of ~30 ps and hermetic coverage up to a pseudo-rapidity of $|\eta|$=3. The precision time information from the MIP timing detector (MTD) will serve as an excellent time-of-flight detector for particle identification in QCD and heavy-ion physics. Together with the wide coverage of tracker and calorimetry, the MTD will enable a broad range of new and unique opportunities in heavy-ion physics at CMS. We present the current status and ongoing R&D of the MTD and performance of extending heavy-ion physics program at CMS with particle identification, focusing on measurements involving hard probes such as heavy flavor hadron reconstruction over wide rapidity down to a very low transverse momentum, correlations of jets and identified hadrons.

Speaker: Geonhee Oh (University of Illinois at Chicago (US))

HP2020_Geonhee_MTD.pdf

Recording

230 The Forward Rapidity Upgrade for the STAR Detector

The STAR Collaboration designs, constructs, and installs a suite of new detectors in the forward rapidity region (2.5<$\eta$<4) over the next two years, enabling a program of novel measurements in pp, pA, and AA collisions. This extension of STAR’s kinematic reach will allow detailed studies of cold QCD physics at both very high and very low partonic momentum fraction, i.e., when the colliding quarks and gluons carry very large or very small amounts of the nucleon energy. Previous STAR efforts using the Forward Pion Detector (FPD) and Forward Meson Spectrometer (FMS) detectors have demonstrated that there are outstanding QCD physics opportunities in the forward rapidity region. To fully explore these physics opportunities, the forward upgrade [1] has detection capability for neutral pions, hadrons, photons, electrons, and jets, and adds charged-particle tracking, electromagnetic, and hadronic calorimetry to STAR’s capabilities at high pseudorapidity. The upgrade will greatly expand the kinematic reach for ongoing measurements of the spin and flavor structure of the nucleon, and will enable studies of the longitudinal structure of the nuclear initial state that leads to breaking of boost invariance in heavy-ion collisions. Transport properties of the hot and dense matter formed in heavy-ion collisions will also become accessible with the new measurement capabilities at forward rapidity. Details on the planed upgrade and the scientific opportunities it will enable will be presented.

Reference:
[1] The STAR Forward Calorimeter System and Forward Tracking System, https://drupal.star.bnl.gov/STAR/starnotes/public/sn0648

Speaker: Dr James Brandenburg (Brookhaven National Laboratory)

jdb_STAR_Forward_Rapidity.pdf

Recording

12:15 Coffee break

Parallel: H1 - Jets and High-PT Hadrons XI

P2

Convener: Gunther Roland (Massachusetts Inst. of Technology (US))

231 Gradient Tomography of Jet Quenching in Heavy-ion Collisions

Transverse momentum broadening and energy loss of a propagating parton are dictated by the space-time profile of the jet transport coefficient $\hat q$ in dense QCD medium. Spatial gradient of $\hat q$ perpendicular to the propagation direction can lead to a drift and asymmetry in parton transverse momentum distribution. Such an asymmetry depends on both the spatial position along the transverse gradient and path length of a propagating parton as shown by numerical solutions of the Boltzmann transport in the simplified form of a drift-diffusion equation. In high-energy heavy-ion collisions, this asymmetry with respect to a plane defined by the beam and trigger particle (photon, hadron or jet) with a given orientation relative to the event plane is shown to be closely related to the transverse position of the initial jet production in full event-by-event simulations within the linear Boltzmann transport model. Such a gradient tomography can be used to localize the initial jet production position for more detailed study of jet quenching and properties of the quark-gluon plasma along a given propagation path in heavy-ion collisions.

Speaker: Prof. Xin-Nian Wang (CCNU/LBNL)

Recording

xnwang-HP2020.pdf

232 Event-by-event jet anisotropy and hard-soft tomography in heavy-ion collisions

Jet anisotropy can provide insight into the path-length dependence of jet quenching and closely relate to the bulk anisotropy in high energy heavy-ion collisions. We show a weak dependence of colliding energy and jet $p_{T}$ for inclusive jet anisotropy $v^{2}_{jet}$ at different centrality classes within the linear Boltzmann jet transport model coupled with the dynamic evolution of the QGP provided by the 3+1D CLVisc hydrodynamic model with fully fluctuating event-by-event initial conditions. By studying the hard-soft tomography, jet anisotropy follows a similar dependence on the system size as the bulk anisotropy does, and an approximately linear correlation between $v^{2}_{jet}$ and bulk $v_{2}$ is observed. In the meantime, jet triangle flow coefficient $v^{3}_{jet}$ shows a small but not vanishing value due to the initial fluctuation and jet quenching.

Speaker: Yayun He

Recording

YayunHe_HP2020.pdf

YayunHe_HP2020_v2.pdf

233 Studies of quark-like and gluon-like contributions to jets using jet charge measurements in pp and PbPb collisions with the CMS experiment

Jets can be used to study in-medium modifications of the parton shower and the energy loss mechanisms in heavy-ion collisions. Several recent works have alluded to a modification in the fractions of quark and gluon jets in QGP due to color-charge dependent quenching. The jet charge is defined as the momentum-weighted sum of charges of particles inside a jet. The sensitivity of jet charge to the electric charge of the initiating parton can be used to discriminate between jets of different origins. In this talk, the unfolded jet charge distributions are presented using data with pp and PbPb collisions at 5.02 TeV collected by the CMS experiment. A template-fitting method is presented to extract the quark-like and gluon-like jet fractions in pp and PbPb collisions using templates from simulations. We also present a jet charge based tagging technique to decompose the inclusive jet shape measurements into the respective quark-like and gluon-like jet shape distributions. These results provide crucial input towards a better understanding of the flavor-dependent medium modifications of the parton shower.

Speaker: Dhanush Anil Hangal (University of Illinois at Chicago (US))

HP2020_DhanushHangal_Jun4.pdf

Recording

234 Measurements of photon- and Z-tagged jet quenching by ATLAS

Measurements of hard-scattered partons produced in conjunction with a high-pT photon or Z boson offer a discerning way to study the quark gluon plasma (QGP) created in ultrarelativistic nucleus-nucleus collisions. The high-pT boson tags the initial energy, direction, and flavor of the opposing parton or partons before they begin to shower and propagate through the QGP, offering a valuable handle for understanding the mechanism of parton energy loss.
ATLAS has performed detailed measurements of the photon-jet transverse momentum balance and the jet fragmentation function in 2015 Pb+Pb data. The significantly larger luminosity of 2018 Pb+Pb data delivered by the LHC, in addition to improvements to the electron reconstruction in
heavy ion events, have enabled qualitatively new measurements in these channels with the ATLAS detector, including the first Z-tagged measurements of partonic energy loss and modification.
In this talk we will present the newest measurements of the energy loss of partons created in coincidence with a high-pT Z boson in Pb+Pb collisions without any formal requirement on a reconstructed jet, comparing the results to predictions provided by multiple models. Prospects for further measurements requiring a reconstructed jet opposite an electroweak boson in the full Run 2 dataset will be discussed, as well as possible future observables in Run 3.

Speaker: Jeff Ouellette (University of Colorado Boulder (US))

JOuelletteHardProbes2020.pdf

Recording

235 Evolution of jet shapes and fragmentation functions in Au+Au collisions at $\sqrt{s_\mathrm{NN}}=200$ GeV with the STAR experiment at RHIC

The modification of jet substructure in heavy-ion collisions compared to that in the vacuum reference is one of the main features of jet quenching. Such modification has been observed at LHC kinematics with various observables, such as jet fragmentation and jet shapes. In this talk, we report measurements of the differential jet shape and semi-inclusive jet fragmentation functions in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV with the STAR detector at RHIC.

Based on the semi-inclusive population of jets recoiling from a high-$\it{p}_{T}$ trigger hadron, the fragmentation functions are constructed from the fraction of the transverse momentum of charged particles projected onto the jet axis over that of the jet. The fragmentation functions are corrected for uncorrelated background effects and instrumental effects via the Mixed-Event technique and unfolding, and the results for central and peripheral collisions will be compared. Similarly, the differential jet shape, $\rho(r)$, is defined as the average fraction of the transverse momentum contained inside an annulus with inner radius $r_a = r-\delta/2$ and outer radius $r_b = r+\delta/2$. The differential jet shapes will be measured for full (charged + neutral) jets at low $\it{p}_{T}$ (10-40 GeV/$\it{c}$) using constituent information jet-by-jet. This kinematic range will provide a complementary measurement to the LHC to demonstrate whether there is a modification and a broadening of the jet profile at RHIC energies. The differential jet shapes will explore the dependence of modifications based on jet size ($R$), centrality, event-plane angle (defined by the beam direction and the vector of the impact parameter), and additionally include a comparison to baseline p+p collisions. Both jet fragmentation function and jet shape results indicate medium-induced modifications in heavy-ion collisions.

Speaker: Joel Mazer (Rutgers University)

HardProbes2020_JetShapeFF_JoelMazer.pdf

Recording

Parallel: H2 - Jets and High-PT Hadrons X

Convener: Brian Cole (Columbia University (US))

236 Open and hidden strangeness production study via high pT dihadron correlations in pp and p-Pb collisions with ALICE at the LHC

Complementary to jet reconstruction, two-particle correlations in $\Delta\eta$ and $\Delta\varphi$ are used to study jets, and in particular their particle composition. While in Pb-Pb collisions this is done to characterize the quark-gluon plasma, pp and p-Pb collisions serve as a reference and are of interest on their own for their input into the understanding of particle production mechanisms. Recent ALICE results on the production of strange particles in small systems (pp and p-Pb collisions) reveal the possibility of having similar strange hadron production mechanisms in all collision systems. We study the production mechanism of hidden strangeness ($\phi$ meson) and open strangeness ( $K_S^0$ meson and $\Lambda$ ($\bar{\Lambda}$) baryon) in jets via two-particle correlations between the strange hadrons and charged primary hadrons in pp collisions at $\sqrt{s} = 13~\rm{TeV}$ and p-Pb at $\sqrt{s_{NN}} = 5.02~\rm{TeV}$ collected with the ALICE experiment at the LHC.

In this talk, the dependence of the per-trigger yields of strange hadrons on the transverse momenta of the trigger and associated particles, as well as on the event multiplicity, will be presented on both the near-side and away-side of the h-V$^0$ and h-$\phi$ correlation functions. Moreover, the ratios of these yields to the yields extracted from the h-h correlation function will be shown. The presented results will be compared among the three hadron species. In addition, a comparison to different MC generators will be presented, which will allow us to better understand differences in the production of open strange mesons, baryons and hidden strange resonances.

Speaker: Lucia Anna Husova (Westfälische Wilhelms-Universität Münster (DE))

husovaHP.pdf

Recording

237 Getting into the Swing of things in Heavy Ion Collisions

In proton-proton collisions the underlying event is rather well
reproduced by general purpose event generators such as Herwig, Pythia
and Sherpa. The key to this success has been the modelling of
multi-parton interactions (MPI). Since long it has been recognised
that the (semi-) soft partonic sub-scatterings in such a scenario
cannot be treated completely independent and the concept of "colour
reconnections" was introduced, where the hadronising strings in an
event may be spanning partons from several different sub scatterings.

The Anganty model for generating fully hadronic exclusive final states
in heavy ion collisions in Pythia8 originally did not include any
collective effects. Rather it simply stacked a number nucleon-nucleon
collisions from Pythia on top of each other, without allowing any
crosstalk. Nevertheless Angantyr is able to reproduce fairly well
general features of events in pA and AA, such as multiplicity and
transverse momentum distributions of charged particles.

In this talk I will present the so-called Swing model for colour
reconnectsions, which originally was developed for the Ariadne/DIPSY
program. Contrary to the standard reconnection models (eg. the ones
implemented for pp in Pythia), the swing is applied already on the
perturbative level and will also affect jet evolution. This model is
now being implemented in the Pythia8/Angantyr program where it allows
for colour reconnections between partons from different
nucleon-nucleon sub-collisions in pA and AA. This requires a proper
treatment of the space-time structure of heavy ion collisions in
general, and in particular of the jet evolution in such events. I will
present preliminary preliminary results from this model with emphasis
on jet-related observables.

Speaker: Leif Lönnblad (Lund University (SE))

HP2020.pdf

Recording

238 The dynamics of leading jets and the jet energy loss

In heavy-ion collisions the Quark Gluon Plasma (QGP) is recreated which is believed to have filled our universe shortly after the Big Bang. The quenching of highly energetic jets which are also produced in these collisions are powerful probes of the QGP. We propose the measurement of leading and subleading jets as a new probe of the underlying dynamics of the QGP. The dynamics of leading jets are significantly more complicated than inclusive jets but allow for a more precise use of jets as probes of the underlying parton dynamics that carry information about the QGP. In particular, leading jets allow for a definition of the so-called jet energy loss at the cross section level. The measurement of subleading jets further allows for a quantitative exploration of how the lost energy is distributed in the final state phase space. We present results for the factorization and evolution of leading and subleading jets both in proton-proton and heavy-ion collisions and outline possible measurements to better illuminate the interaction of the QGP with hard probes.

Speaker: Felix Ringer (Lawrence Berkeley National Laboratory)

HP20_FRinger.pdf

Recording

239 Jets are modified at both high and low virtuality

Jet modification is a multi-stage (multi-scale) process: an initial high virtuality stage gives way to a lower virtuality transport stage for high energy partons, and a strongly coupled phase for lower energy parts of the shower. The transition from the high virtuality medium-modified DGLAP stage takes place when the virtuality reaches the medium induced scale $\hat{q} \tau$, where $\tau$ is the lifetime of a given parton. A recent outstanding dispute has arisen on the role of energy loss in the high virtuality phase, and its contribution to jet observables $^{[1,2]}$. In this presentation, we demonstrate that in a realistic dynamically evolving medium, the effect of the higher virtuality stage on leading hadron suppression is comparable or dominant to the lower virtuality stages. This is due to the fact that, for most jets, $\hat{q}$ scales with entropy density, and thus falls faster than the virtuality of the leading partons. As a result, the combined lifetime of partons with virtuality larger than the medium induced scale is sufficiently long that these partons scatter with the plasma multiple times before reaching the medium scale.

To systematically address this, we derive the complete next-to-leading twist single gluon emission contribution. Going beyond previous work, we include higher-twist contributions from both the modulus of the amplitude and the phase in interference terms. We also include all momentum fraction ($y$) suppressed contributions from quark scattering prior to emission. This calculation allows us to successfully address the issues raised in the work by Aurenche et al. $^{[3,4]}$. Based on this formalism, a Monte-Carlo framework (MATTER+LBT+hydrodynamics) is further developed for simulating parton showers through the QGP. We demonstrate that while the medium-modified DGLAP process dominates jet observables at high $p_T$, the subsequent near-on-shell transport process dominates at low $p_T$. Only by combining these two stages can we naturally obtain a simultaneously good description of the nuclear modification factors of hadrons and jets.

References:
1. Caucal, P., Iancu, E., Mueller, A. H., & Soyez, G. (2018). Vacuumlike jet fragmentation in a dense qcd medium. Physical review letters, 120(23), 232001.
2. Casalderrey-Solana, J., Mehtar-Tani, Y., Salgado, C. A., & Tywoniuk, K. (2013). New picture of jet quenching dictated by color coherence. Physics Letters B, 725(4-5), 357-360.
3. Aurenche, P., Zakharov, B. G., & Zaraket, H. (2008). Failure of the collinear expansion in the calculation of the induced gluon emission. JETP letters, 87(11), 605-610.
4. Aurenche, P., Zakharov, B. G., & Zaraket, H. (2008). Comment on``Success of collinear expansion in the calculation of induced gluon emission''. arXiv preprint arXiv:0806.0160.

Speaker: Abhijit Majumder (Wayne state university)

majumder_HP20.pdf

Recording

240 Gamma-hadron spectra in $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

Under the assumption that a quark-gluon plasma droplet is produced in $p$ + A collisions, $\gamma$-triggered hadron spectra [1,2] are studied within a next-to-leading-order perturbative QCD parton model with the medium-modified parton fragmentation functions in $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The initial conditions and space-time evolution of the small system of hot and dense medium is simulated by superSONIC hydrodynamic model [3] and parton energy loss in such a medium is described by the high-twist (HT) approach [4]. The scaled jet transport coefficient $\hat{q}/T^3$ in this HT approach is extracted from single hadron in central A + A collisions because its values from single and dihadron suppressions are similar [5]. Numerical results show that $\gamma$-hadron spectra for $p_T^\gamma=12-40$ GeV/$c$ in this scenario are suppressed by 10% $\sim$ 20% in the most central 0 - 10% $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The suppression becomes weaker with higher transverse momentum of the triggered-$\gamma$. As a comparison, $\gamma$-hadron suppression in Pb + Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ and 5.02 TeV is also predicted.

References
[1] X. N. Wang, Z. Huang and I. Sarcevic, Phys. Rev. Lett. 77, 231 (1996)
[2] H. Zhang, J. F. Owens, E. Wang and X. N. Wang, Phys. Rev. Lett. 103, 032302 (2009)
[3] R. D. Weller and P. Romatschke, Phys. Lett. B 774, 351 (2017)
[4] W. t. Deng and X. N. Wang, Phys. Rev. C 81, 024902 (2010)
[5] M. Xie, S. Y. Wei, G. Y. Qin and H. Z. Zhang, Eur. Phys. J. C 79, no. 7, 589 (2019)

Speaker: Man Xie (Central China Normal University)

arXiv:2003.02441

Recording

xieman-gam-had-hp2020.pdf

Parallel: H3 - Heavy Flavor X

Convener: Giulia Manca (Universita` degli studi di Cagliari and INFN, Cagliari, IT)

241 Beauty production with ALICE at the LHC

In hadronic collisions, beauty quarks are produced in hard scattering processes with large momentum transfer. Their production provides a very important test of perturbative QCD calculations in pp collisions.
In heavy-ion collisions, the measurement of beauty hadron production is a unique tool to investigate the properties of the Quark-Gluon Plasma. In particular, beauty quarks, being four times heavier than charm quarks, can be utilized to study the in-medium mass dependent energy loss. In addition, measurements in p-Pb collisions are crucial to investigate the effects of cold nuclear matter on their production.

With the ALICE detector, beauty quarks are studied by measuring electrons and non-prompt D mesons coming from beauty hadron decays at mid-rapidity. Finally, a more direct access to the initial parton kinematics is obtained by measuring beauty-tagged jets. They can provide further constraints for energy loss models adding information on how the radiated energy is dissipated.

In this contribution, the latest measurements of beauty production using beauty-decay electrons, non-prompt D-mesons and beauty-tagged jets in pp collisions at $\sqrt{s}$ = 5.02 TeV, and their comparison to pQCD calculations will be presented. New measurements of beauty-tagged jet production down to low $p_{\rm T}$ in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be discussed. The latest results on the centrality dependence of $R_{\rm AA}$ of beauty-decay electrons and non-prompt D mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared to different theoretical models will be presented.

Speaker: Mengke Cai (Central China Normal University)

HP2020_BProduction_MCai_1.pdf

Recording

242 Measurement of quarkonium polarization in Pb-Pb collisions at the LHC with ALICE

Polarization measurements represent an important tool for understanding the particle production mechanisms occurring in proton–proton collisions. In particular, for quarkonium states, the very small polarization measured at the LHC represents a serious and a long-lasting challenge for theoretical models. When considering heavy-ion collisions, particle polarization could also be used to investigate the characteristics of the hot and dense medium (Quark-Gluon Plasma) created at LHC energies. Recently, it has been hypothesized that quarkonium states could be polarized by the strong magnetic field generated in the early phase of the evolution of the system.
In ALICE, the quarkonium polarization is extracted by measuring the anisotropies in the angular distribution of the muons coming from the quarkonium state decay. In this contribution, final results on the J/$\psi$ and new results on the $\Upsilon(1S)$ polarization in Pb-Pb collisions at a center of mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV will be presented. The $p_{\rm T}$-differential measurement was done at forward rapidity (2.5 $<$ y $<$ 4) and the results will be shown in two different reference planes. The results will be also compared with previous measurements from pp collisions. Finally, the status of the analysis dedicated to measure the J/$\psi$ polarization as a function of the collision centrality as well as relative to the event plane will be discussed.

Speaker: Luca Micheletti (Universita e INFN Torino (IT))

quarkonium_polarization.pdf

Recording

243 Open heavy flavour production in heavy ion collisions

Heavy flavor observables provide valuable information on the properties of the hot and dense quark gluon plasma (QGP) created in ultrarelativistic nucleus-nucleus collisions. Various microscopic models have successfully described many of the observables associated with its formation. Their transport coefficients differ, however, due to different assumptions about the underlying interaction of the heavy quarks with the plasma constituents, different initial geometries and formation times, different hadronization processes, and a different time evolution of the QGP as well as by different transport equations for the heavy quarks. Recently the different groups joined efforts to investigate systematically how these assumptions influence the heavy quark properties at the end of the QGP expansion. For this purpose the same initial condition and the same model for the QGP expansion has been imposed on these models and the influence on RAA and v2 as well as the difference in box calculations has been studied. We report about these results and identify what steps are necessary to reduce the present ambiguities.

Y. Xu et al. Phys.Rev. C99 (2019) 014902
S.Cao et al. Phys.Rev. C99 (2019) 054907
T. Song et al. arXiv:2001.07951

Speaker: joerg aichelin (Subatech/CNRS)

HP2020_aichelin.pdf

Recording

244 Radial profile of heavy quarks in jets in high-energy heavy-ion collisions

Heavy flavor physics in high-energy heavy-ion collisions is a promising and active area to study the `` jet quenching " effects both at the RHIC and the LHC. The recent reported $D^0$ meson radial profiles in jets measured by CMS collaboration provide new experimental constraints on the mechanisms of heavy flavor production in proton-proton collisions and give new insights into the in-medium interaction mechanisms of heavy quarks inside the quark-gluon plasma (QGP). In this talk, we present the first theoretical calculations of the charm and bottom radial distributions relative to the jet axis both in p+p and Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$TeV. In our work, the in-medium parton propagations are described by a Monte Carlo transport model which uses the next-to-leading order (NLO) plus parton shower (PS) event generator SHERPA as input and includes elastic (collisional) and inelastic (radiative) interaction for heavy quarks as well as light partons, the cold nuclear matter(CNM) effects are also taken into accout. Our simulated results show that, at low $D^0$ $p_T$, the radial distribution shifts to larger radius indicating a strong diffusion effect of charm quarks due to the in-medium interactions, but no significant modification observed at high $D^0$ $p_T$, which are consistent with the experimental data. In the further study, we estimate the net effect on the heavy quark diffusion from collisional and radiative mechanism, and demonstrate the $p_T$ dependence of this diffusion effect. We find that collisional process has significant effects at low $p_T$, especially dominates at $0-5$GeV, and the radiative process has a non-zero effect even at high $p_T\sim 50$GeV. The total diffusion effect decreases with charm $p_T$ which explains the significant modification at low $D^0$ meson $p_T$ observed in experiment. As for the bottom quarks, no significant modification on their radial profile in jets is observed in A+A collisions. Actually, due to the mass effect, the in-medium diffusion effects of bottom quarks are smaller both in collisional and radiative interaction relative that of charm quarks. Our study suggests more precise measurements on the charm and bottom radial distributions in jets in heavy ion collisions to disentangle the contributions from collisional and radiaive energy loss, especially at $p^Q_T <20$GeV.

Speaker: Sa WANG (Central China Normal University)

HP2020_SAWANG.pdf

Recording

245 Fragmentation of J/$\psi$-jets in PbPb collisions with the CMS experiment

J/$\psi$ mesons have been found to be produced with more jet activity than predicted by models in pp collisions at the LHC. J/$\psi$ production has long been known to be modified in nuclear collisions, via Debye screening, as well as by other effects. Indirect evidence, in particular, the non-vanishing $v_{2}$ of J/$\psi$ at large transverse momentum, however, suggests that jet quenching may also play an important role in J/$\psi$ suppression. We present the first measurement of reconstructed J/$\psi$-jets in heavy-ion collisions. We measure the jet fragmentation function of jets containing a J/$\psi$ meson, to study the dependence of quenching effects on the degree of associated hadro-production inside the jet.

Speaker: Batoul Diab (Centre National de la Recherche Scientifique (FR))

HP2020_BatoulDiab.pdf

Recording

Parallel: H4 - New Theoretical Developments II

Convener: Hannah Elfner

246 Heavy flavor hadronization and hadron chemistry in heavy-ion collisions

A solid hadronization model is essential for understanding hadronic observables in high-energy nuclear collisions, while still remains a challenge due to its non-perturbative nature. We have developed an advanced hadronization model for heavy quarks [1] and studied their suppression, flow and hadron chemistry in heavy-ion collisions. A complete set of both $s$ and $p$-wave hadronic states are included, which naturally cover all major heavy flavor hadron states observed in the Particle Data Group, and normalize the coalescence probability of zero momentum heavy quarks with proper hadron sizes. With a strict energy-momentum conservation implemented, the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum are guaranteed.

By combining this newly developed hadronization scheme with the state-of-the-art Langevin-hydrodynamics model [2] that incorporates both elastic and inelastic energy loss of heavy quarks inside the realistic QGP medium, we provide a good description of the nuclear modification factor and elliptic flow of $D$ mesons, as well as the corresponding flavor hierarchy between $D$ and $B$-decayed electrons. A good description of the charmed hadron chemistry -- both $p_\mathrm{T}$-integrated and differentiated $Λ_c$/$D^0$ and $D_s$/$D^0$ ratios -- is also obtained. Our study indicates that the in-medium size of charmed hadrons should be larger than the size in vacuum, which can be tested by hadronic model calculations. It is also found that the inclusion of the $p$-wave states and the radial flow of the QGP is crucial for understanding the chemical composition of charmed hadrons observed in relativistic heavy-ion collisions.

[1] S. Cao, K.-J Sun, S. Liu, W.-J Xing, G.-Y. Qin and C.-M. Ko, arXiv:1911.00456.
[2] S. Cao, G.-Y. Qin and S.A. Bass (2015) Phys. Rev. C92 024907 (arXiv:1505.01413)

Speaker: Shanshan Cao (Wayne State University)

HP2020.pdf

Recording

247 Lattice QCD calculation of $\hat{q}$ with dynamical fermions

The jet transport coefficient $\hat{q}$ is the leading property of a strongly interacting medium that effects jet propagation. It introduces momentum transverse to a jet parton’s direction, changing its virtuality and thus controls the modification of hard jets in a dense extended medium. In this talk, we present the first unquenched lattice QCD calculation of $\hat{q}$. The calculation is carried out using (2+1)-flavors of quarks, using the highly improved staggered quark action (HISQ) and tree-level Symanzik improved gauge action. The calculation is performed in a wide range of temperatures, ranging from 200 MeV $\lt T \lt$ 800 MeV using the MILC code package.

Following earlier work in quenched SU(2) and SU(3) [1,2], we considered a single hard parton scattering off the glue field of a thermal QCD medium by exchanging a Glauber gluon (whose transverse momentum is larger than its longitudinal components). The hard scale associated with the jet parton allows the coupling of the gluon to that parton to be treated in perturbation theory. The coupling of the gluon to the medium is treated non-perturbatively. This non-perturbative part is expressed in terms of a non-local (two-point) Field-Strength-Field-Strength operator product which can be Taylor expanded after analytic continuation to the deep-Euclidean region. Such an expansion allows us to write $\hat{q}$ in terms of the expectation of a diminishing series of local operators, which are suppressed by factors of the hard parton energy. We also discuss the connection between our formalism and a method outlined in Ref. [3] that allows one to extract light-cone correlations using the matrix elements of frame-dependent, equal-time correlators in the large momentum limit. The calculated $\hat{q}$ and its temperature dependence demonstrates considerable agreement with the phenomenological extractions carried out by the JET collaboration.
[1] A. Kumar, A. Majumder, C. Nonaka, PoS LATTICE2018 169 (2018),
arXiv: 1811.01329 [nucl-th].
[2] A. Majumder, Phys. Rev. C87 034905 (2013).
[3] X. Ji, Phys. Rev. Lett. 110, 262002 (2013).

Speaker: Amit Kumar (Wayne State University)

AmitKumar_HardProbes2020_upload.pdf

Recording

248 Beyond the wake: Hydrodynamic and non-hydrodynamic response of an expanding Quark-gluon plasma to a moving energetic probe

We study the response of a Bjorken-expanding quark-gluon plasma (QGP) to the passage of an energetic parton through it. We compute the non-equilibrium stress-energy tensor induced by such moving energetic parton using linearized Boltzmann equation under the relaxation time approximation. At large distances and large Bjorken time, the QGP exhibits hydrodynamic response, meaning the disturbance induced by the energetic parton forms a Mach cone and diffusive wake. However, the transition from hydrodynamic response to non-hydrodynamic response occurs at the intermediate distances and times. We will characterize the features of the non-hydrodynamic response due to the competition among multiple time scales of the problem: the expansion rate of the medium, the equilibration rate of the medium and the rate of energy/momentum loss of the energetic parton. Finally, we will discuss the phenomenological implication of our study.

Speaker: Dr Yi Yin (Institutite of Modern Physics (Lanzhou), CAC)

HP_nonhydro_response_YiYin.pdf

Recording

249 Photon-jet angular correlations in high energy proton-nucleus collisions: from low to high transverse momenta

We calculate the double differential cross section for production of a quark parton and a photon in proton-nucleus collisions using a newly proposed formalism which generalizes the Color Glass Condensate approach by including large x gluons of the target. We investigate transverse momentum, rapidity and A dependence of azimuthal angular correlations between the produced parton and the photon in different collision kinematics.

Speaker: Jamal Jalilian-Marian (Baruch College, CUNY)

hp2020.pdf

Recording

250 Photon radiation in hot nuclear matter by means of chiral anomalies

A new mechanism of photon emission in the quark-gluon plasma is proposed. Photon dispersion relation in the presence of the CP-odd topological regions generated by the chiral anomaly acquires an imaginary mass. It allows photon radiation through the decay $q→q\gamma$ and annihilation $q \bar q→\gamma$ processes closely related to the chiral Cherenkov radiation. Unlike previous proposals this mechanism does not require an external magnetic field. The differential photon emission rate per unit volume is computed and shown to be comparable to the rate of photon emission in conventional processes. The presentation is based on Phys.Rev. C99 (2019) no.6, 064907, Phys.Rev.Lett. 121 (2018) no.18, 182301.

Speaker: Prof. Kirill Tuchin (Iowa State University)

Recording

Tuchin.pdf

Friday 5 June

Plenary: Future Facilities

Plenary

Convener: Berndt Mueller (Brookhaven National Laboratory)

251 Future Facilities: RHIC Plans

Speaker: Rosi Reed (Lehigh University)

Recording

RReedHP2020v3Final.pdf

252 Future Facilities: LHC Plans

Speaker: Inna Kucher (Centre National de la Recherche Scientifique (FR))

LHC_Upgrades_IKucher_HP2020.pdf

Recording

253 Future Facilities: FCC

Speaker: Guilherme Milhano (LIP-Lisbon & CERN TH)

FCCMilhanoFINAL.pdf

Recording

254 Future Facilities: EIC

Speaker: Elke-Caroline Aschenauer (BNL)

eca.EIC.overview.pptx

Recording

09:40 Break

Plenary: Flash Talks and Summary I

Plenary

Convener: Marco Van Leeuwen (Nikhef National institute for subatomic physics (NL))

255 Flash Talk 1

Speaker: Timothy Thomas Rinn (University Of Illinois (US))

Recording

trinn_flashtalk.pdf

256 Flash Talk 2

Speaker: Lin Chen (Central China Normal University)

flash.pdf

Recording

257 Flash Talk 3

Speaker: Wenkai Zou (Columbia University (US))

hp2020_wzou_flash_talk.pdf

258 Flash Talk 4

Speaker: Oscar Garcia Montero (Karl-Ruprechts-Universität Heidelberg)

HBT_FT.pdf

Recording

259 Flash Talk 5

Speaker: Jonghan Park (Inha University (KR))

jonghan_flashtalk_v2.pdf

Recording

260 Flash Talk 6

Speaker: Saehanseul Oh (LBNL)

JetFF_HP_SaehanseulOh.pdf

Recording

261 Flash Talk 7

Speaker: Desmond Mzamo Shangase (University of Michigan (US))

Cold QCD Physics with sPHENIX.pdf

262 Flash Talk 8

Speaker: Quinn Brodsky (Massachusetts Institute of Technology)

HardProbes_flashtalk.pdf

Recording

263 Summary: Electroweak Physics

Speaker: Dr Rupa Chatterjee (Variable Energy Cyclotron Centre)

electroweak_summary_HP2020.pdf

Recording

264 Summary: Saturation and Initial State

Speaker: Bjoern Schenke (Brookhaven National Lab)

HP2020-schenke.pdf

Recording

11:15 Break

Plenary: Summary II and Closure

Plenary

Convener: Silvia Masciocchi (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

265 Summary: Jets and High-PT

Speaker: Jana Bielcikova (Czech Academy of Sciences (CZ))

HP_jetsummary_final_1.pdf

Recording

266 Summary: Heavy Flavor and Quarkonia

Speaker: Roberta Arnaldi (Universita e INFN Torino (IT))

HP20_Arnaldi.pdf

Recording

267 Introduction of Hard Probes 2022

Speaker: Silvia Masciocchi (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

HP2022_at_HP2020.pdf

HP2022 video

Recording

268 Close and Adjourn

Speakers: Christina Markert (University of Texas at Austin (US)), Claudia Ratti (University of Houston), Frank Geurts (Rice University (US)), Rainer Fries (Texas A&M University)

Recording