Hard Probe 2016

22 Sept 2016, 08:00 → 27 Sept 2016, 20:00 Asia/Chongqing

East Lake International Conference Center

Ben-Wei Zhang (Central China Normal University), Daicui Zhou (Central China Normal University CCNU (CN)), Xin-Nian Wang (Lawrence Berkeley National Lab. (US))

The 8th International Conference on Hard and Electromagnetic Probes of High-energy Nuclear Collisions (Hard Probes 2016) will be held at the East Lake International Conference Center, Wuhan, China on September 23 -27, 2016. The conference will be hosted by Central China Normal University (CCNU). A one-day of pedagogical lectures for students and young scientists will be held on the campus of CCNU on September 22.

Hard and electromagnetic probes are powerful tools for the investigation of properties of hot QCD matter in relativistic heavy-ion collisions. They provided essential evidence for the formation of a strongly coupled quark-gluon plasma (sQGP) in heavy-ion collisions at RHIC and LHC. Recent new developments in theory, experiment and phenomenology will lead to quantitative characterization of properties of the sQGP and discovery of new phenomena at RHIC, LHC and future collider energies. The Hard Probes conference series is an important forum to discuss the current status, progress and future perspectives on hard probes and related topics.

The Hard Probes 2016 conference will consist of invited plenary talks, contributed parallel talks and poster presentations. Topics for discussion will include:

• - Jet production and modification in QCD matter
• - High p_T hadron spectra and correlations
• - Jet-induced medium excitations
• - Jet properties in small systems
• - Heavy flavor hadrons and quarkonia
• - Photons and dileptons
• - Initial state and related topics

Thursday, 22 September

1 Heavy quark/quarkonium transport

Speaker: Pengfei Zhuang (Tsinghua University)

HP2016_StudentDay_Zhuang.pptx

10:00 Break and Photo

2 Heavy flavor/quarkonium experiment

Speaker: Lijuan Ruan

HP2016Lecture_LijuanRuan .pdf

HP2016Lecture_LijuanRuan.ppt

3 EM experiment

Speaker: Axel Drees (Stony Brook University)

Drees_StudentLecture_HD16 v1.pptx

12:30 Lunch

4 Parton propagation in medium

Speaker: Yacine Mehtar-Tani (INT, University of Washington)

HP2016-lecture.pdf

15:00 Break

5 Jets experiment

Speaker: Matthew Nguyen (Centre National de la Recherche Scientifique (FR))

StudentLectureHP_MAN_20160922.pdf

6 Jet physics theory

Speaker: Matteo Cacciari (LPTHE Jussieu)

jets.pdf

Friday, 23 September

Plenary Session I: Experimental Reports I

Convener: Federico Antinori (Universita e INFN, Padova (IT))

7 Welcome

8 Report from ALICE

Speaker: Xiaoming Zhang (CERN)

ALICEOverviewHP.pdf

9 Report from ATLAS

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

1-2-HP16-AtlasOverviewV1-23092016.pdf

10 Report from CMS

Speaker: Doga Can Gulhan (CERN)

HPCMSOverviewFinal.pdf

10:30 Break

Plenary Session II: Experimental Reports II

Convener: Enke Wang (Central China Normal University)

11 Report from LHCb

Speaker: Yanxi Zhang (Laboratoire de l'Accelerateur Lineaire (FR))

2-1-HeavyIonLHCb_HardProbes_Yanxi.pdf

12 Report from PHENIX

Speaker: Xiaochun He (Georgia State University)

2-2-HP2016_PHENIX_HE.pptx

13 Report from STAR

Speaker: Bingchu Huang (University of Illinois at Chicago)

Bingchu_HP2016.pdf

12:30 Lunch

Plenary Session III: Heavy-ion Theory

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

14 Theory overview

Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))

armesto_HP2016.pdf

15 Hard probes on the Lattice

Speaker: Olaf Kaczmarek (University of Bielefeld)

Kaczmarek_HP16.pdf

16 IS of Heavy-Ion collisions and Hard probes

Speaker: Raju Venugopalan (Brookhaven National Laboratory)

HardProbes2016_Raju.pdf

15:40 Break

Plenary Session IV: Jet Theory

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

17 Jet substructure

Speaker: Matteo Cacciari (LPTHE Jussieu)

jets-substructure.pdf

18 Jets in strong coupling

Speaker: Jorge Casalderrey Solana (University of Barcelona (ES))

2-2 jcs_talk.pdf

Poster Session

POSTER ID PrimaryAuthor Title
1 "UERMOESSY, Karoly" "Statistical Hadronisation in ep, ee, pp and AA Collisions"
2 "LOKHTIN, Igor" Medium-modified jets at the LHC in PYQUEN model
3 "SEKIHATA, Daiki" Analysis of neutral mesons in pp and Pb-Pb collisions with the PHOS detector in the ALICE-Run2
4 "KAR, Somnath" Measurement of angular correlations between D mesons and charged particles in pp and p-“Pb collisions with ALICE at the LHC
5 "OLIVEIRA DA SILVA, Antonio Carlos" Prospects for the measurement of D mesons in jets in Pb-Pb collisions with ALICE at the LHC
6 "ZHAO, Ye-yin" "Two-gluon rapidity correlations of strong colour field in $pp$, $pA$ and $AA$ collisions"
7 "Mr. Bíró, Gábor" The Energy Evolution of the Non-Extensive Theory Parameters in Proton-Proton Collisions from RHIC to LHC Energies
8 "HUANG, Xinjie" J/psi production in Au+Au collisions at √š(s_NN ) = 200 GeV at the STAR experiment
9 "FESTANTI, Andrea" Measurement of the D-meson prompt fraction with a data-driven approach in ALICE
10 "LI, Hanlin" What is producing the charm flow in AA and pA collisions? The AMPT view
11 "BISWAS, Rathijit" Measurement of charged jet cross-section and properties in proton-proton collisions at √šs = 2.76 TeV
12 "Mr. HUANG, Te-chuan" Muon identification with the Muon Telescope Detector at the STAR experiment
13 "Mr. SARKAR, Debojit" Model study of Two Particle Correlations with Identified Trigger Particles in p-Pb collisions at LHC energy
14 "GUO, Yun" Matrix Models for Deconfinement and Their Perturbative Corrections
15 "Dr. CANOA ROMAN, Veronica" Time Projection Chamber TPC for sPHENIX
16 "KIM, Minwoo" Particle-yield modification in jet-like azimuthal di-hadron correlations in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV with ALICE
17 "Dr. MORAD, Razieh" Improving the light quark jet prescription in AdS/CFT
18 "ZHANG, Le; CAO, Shanshan; HOU, Defu; QIN, Guang-you" Medium-induced gluon radiation and parton energy loss with transverse and longitudinal scattering in dense nuclear matter
19 "Chen, Baoyi" charmonium formation process in relativistic heavy ion collisions
20 "Dr. KUMAR, Yogesh" Quark-Gluon plasma equation of state using statistical model
21 "KUMAR, Yogesh" Study on the production of electromagnetic radiation from quark gluon plasma
22 "KE, Weiyao" Constraining longitudinal dependent initial condition from experimental data at LHC
23 "SHOU, Qiye" Measurement of elliptic flow of neutral pions with ALICE-EMCal in Pb-Pb collisions at √šsNN = 2.76 TeV
24 "Dr. ZHAO, Jie" Effects of jet particle correlations on the azimuthal correlator observable for Chiral Magnetic Effect
25 "Dr. DAS, Sabita" "Systematic study of chemical freeze-out in proton-proton collisions at SPS, RHIC and LHC energies"
26 "Prof. HE, Xiaochun" Results of the sPHENIX Prototype Hadronic Calorimeter Beam Test
27 "Jakub Andrzej Kremer" Performance of high-pT electron identification in lead-lead collisions at 5.02 TeV with the ATLAS detector
28 "Piotr Andrzej Janus" Light-by-light scattering in ultra-peripheral Pb+Pb collisions at sqrt{s_NN} = 5.02 TeV with the ATLAS detector
29 "LOPEZ LOPEZ, Jorge Andres" Measurement of J/psi production in 5.02TeV Pb+Pb collisions with the ATLAS experiment
30 "Mr. ABDOLMALEKI, Hamed" The effect of W^2 cut and IC contribution in the proton structure.

18:30 Reception Dinner

Buses leave for Reception dinner at 6:30 PM

Saturday, 24 September

Parallel Session I: EM Probes (I)

Convener: Daimei Zhou (IOPP)

19 Direct photon yield in pp and in Pb-Pb collisions measured with the ALICE experiment

Direct photons are produced at every stage of the nucleus-nucleus collision and therefore they are sensitive to the different phases of the medium evolution. The low-$p_T$ component of the direct photon spectrum is dominated by thermal production in the quark-gluon plasma and during the hadron-gas phase and carries information about the temperature of the emitting medium; for $p_T$ greater than 5 GeV/c, direct photons are mainly produced in hard partonic scattering processes in the early stage of the collision and are not affected by the strongly interacting medium, allowing us to access information on the initial dynamics.

Measurements of direct photon spectra in pp collisions serve both to refine perturbative Quantum Chromodynamics, in particular our knowledge of the parton distribution functions, and as reference for heavy-ion studies.

In this talk, an overview of the most recent ALICE results on direct photon production from pp and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV will be shown in comparison with predictions from hydrodynamic models. The current status of analysis
on direct photon production in pp collisions at $\sqrt{s} = 7$ TeV, using isolation techniques for high-$p_T$ candidates, will also be shown and discussed.

Speaker: Davide Francesco Lodato (Nikhef National institute for subatomic physics (NL))

LodatoSlides_HP_2016_v10.pdf

20 Direct Photon Production at Low Transverse Momentum Measured in PHENIX

The PHENIX experiment discovered a large excess of low-pT direct
photons in Au+Au collisions at 200 GeV compared to reference p+p
collisions, which has been attributed to thermal radiation from the
medium produced in the collisions. At the same time the excess photons
show a large azimuthal anisotropy, expressed as Fourier coefficients
v2 and v3. These surprising results have not
yet been fully described by theoretical models. PHENIX has developed
a new technique to identify conversion photons without assuming the
radius where the conversion happened. This method greatly increases
the avaliable statistics and reduces systematic uncertainties. We
will present the current status of the analysis of low momentum direct photons
converted on the layers of the VTX detector in the 2014 Au+Au dataset,
a major improvement over previously published results.

Speaker: Wenqing Fan (Stony Brook University)

1_2hp2016_wenqing_final.pdf

21 Direct virtual photon production in Au+Au collisions at $ \sqrt{s_{NN}} $ = 200 GeV at STAR

A primary goal of heavy ion physics is to study the fundamental properties of the hot and dense medium created in the ultra-relativistic heavy-ion collisions. The hot, dense medium is expected to emit thermal radiation in the form of direct photons and dileptons. Once produced, photons traverse the medium with minimum interactions. This makes photons an ideal probe of the medium evolution by selecting different kinematics.

The Time-of-Flight detector, which was fully installed in 2010, enables clean electron
identification from low to intermediate transverse momenta ($p_{T}$). The Barrel ElectroMagnetic Calorimeter allows electron trigger and identification at high $p_{T}$. In this talk, we will present the direct virtual photon production for 1<$p_{T}$<3 GeV/$c$ and 5<$p_{T}$<10 GeV/$c$. This measurement is derived from dielectron continuum in the dielectron invariant mass region 0.1<$M_{ee}$<0.28 GeV/$c^{2}$ from one billion $\sqrt{s_{NN}}$ = 200 GeV Au+Au events taken in 2010 and 2011. The centrality dependence of direct virtual photon production will be discussed. Comparisons with model calculations including hadronic and partonic thermal radiation will be shown for the direct virtual photon production in Au+Au collisions.

Speaker: Chi Yang (USTC)

HP2016_V3.pdf

22 A systematic study of electromagnetic radiation and of the collectivity in small quark-gluon droplets

We present a systematic study of electromagnetic radiation and of the hadronic observables in (p, d, $^3$He)+Au collisions at RHIC energies and in p+Pb collisions at the LHC energy. Using a (3+1)-d viscous hydrodynamics + hadronic cascade hybrid framework, the effects of breaking the longitudinal boost-invariance on direct photon and hadronic observables are quantified. Predictions of thermal photon enhancement in high multiplicity pp collisions at 13 TeV and in the recent beam energy scan (d+Au collisions at RHIC energies) will be presented. The role of net baryon density and finite baryon diffusion on direct photon and flow observables will be highlighted for d+Au collisions at 19.6 GeV. The proposed thermal photon enhancement [1] and flow observables at low collision energies can serve as additional signatures for the existence of a hot quark-gluon plasma in small collision systems.

[1] C. Shen, J.-F. Paquet, G. S. Denicol, S. Jeon and C. Gale, Phys. Rev. Lett. 116, no. 7, 072301 (2016)

Speaker: Chun Shen (McGill University)

small_systems_HP2016_ChunShen.pdf

23 Exploring the effects of bulk viscosity on dilepton radiation in high energy nucleus-nucleus collisions

Bulk viscosity has recently been shown to play a major role in describing both photon [1] and hadron [2] observables at the Relativistic Heavy-Ion Cllider (RHIC) and the Large Hadron Collider (LHC). Thermal dilepton production is a particularly interesting electromagnetic probe that, up until now, has not been studied within such simulations. Using the differential nature of the dilepton spectrum, one can isolate radiation originating from different phases of the medium. The partonic sector emits high invariant-mass lepton pairs, while the hadronic sector produces lower invariant mass dileptons. Starting from the IP-Glasma initial conditions as in Refs [1,2], we investigate for the first time thermal dilepton production originating from Pb-Pb collisions at the LHC. A detailed study of the role bulk viscosity plays on the development of anisotropic flow and on thermal dilepton radiation is presented. As reference, a similar calculation will be performed at top RHIC energy, thus allowing comparisons with results from Pb-Pb collisions at the LHC to be made. Consequently, more robust conclusions regarding the role of bulk viscosity in high energy heavy-ion collisions will be drawn.

[1] Jean-François Paquet et al., Phys. Rev. C 93 no. 4, 044906 (2016)
[2] S. Ryu et al., Phys. Rev. Lett. 115 no. 13, 132301 (2015)

Speaker: Gojko Vujanovic (The Ohio State University)

HP_2016_v3.pdf

Parallel Session I: Hard Probes in p+p and p+A Collisions (I)

Convener: David d'Enterria (CERN)

24 ALICE measurements of heavy-flavour production as a function of multiplicity and angular correlations in pp and p--Pb collisions at the LHC

The study of the production of hadrons containing charm and beauty quarks in proton-proton (pp) collisions at the LHC provides a way to test calculations based on perturbative QCD at high collision energy. Heavy-flavour hadron production in p-Pb collisions is sensitive to Cold Nuclear Matter (CNM) effects. In addition to transverse momentum and rapidity differential trends, measurements as a function of multiplicity and of angular correlations provide further constraints on the description of heavy-flavour production in pp and p-Pb collisions. The measurement of heavy-flavour production in pp collisions as a function of the charged-particle multiplicity could provide further insights into the role of multi-parton interactions and the interplay between hard and soft mechanisms in particle production. The multiplicity-differential measurements of heavy-flavour production in p-Pb collisions are sensitive to the dependence of CNM effects on the collision
geometry and on the density of final-state particles. The measurement of azimuthal correlations of D mesons and charged particles in pp collisions provides a way to characterize charm production and fragmentation processes, while in p-Pb collisions they could give insights into possible collective effects in small systems.

Prompt D$^{0}$, D$^{+}$ and D$^{*+}$ meson yields measured as a function of charged-particle multiplicity in pp collisions at $\sqrt{s}$ = 7 TeV will be presented, along with results obtained for inclusive J/$\psi$ and non-prompt J/$\psi$. The measurement of the yields of D mesons and of electrons from heavy-flavour hadron decays as a function of charged-particle multiplicity in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be shown as well. The centrality dependence of heavy-flavour nuclear modification factor will also be discussed.

The measurement of azimuthal correlations of D mesons and charged particles in pp collisions at $\sqrt{s}$ = 7 TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will also be presented.

Comparisons with model calculations will be discussed.

Speaker: Grazia Luparello (Universita e INFN, Trieste (IT))

1-HP2016_v6_withAnimation.pdf

25 Measurement of the nuclear modification factor for high-pT charged hadrons in pPb collisions with the ATLAS detector

The charged hadron spectra in p+Pb and pp collisions at sqrt(s)=5.02TeV are measured with the ATLAS experiment at the LHC. The measurements are performed with p+Pb data recorded in 2013 with an integrated luminosity of 25nb^-1 and pp data recorded in 2015 with an integrated luminosity of 28pb^-1. The p+Pb results are directly compared to pp spectra, as a ratio scaled by the number of binary nucleon-nucleon collisions, the nuclear modification factor RpPb. RpPb allows for a detailed comparison of the collision systems in several rapidity ranges, different centrality intervals and up to high transverse momentum.

Speaker: Petr Balek (Weizmann Institute of Science (IL))

PetrBalek_RpPb.pdf

26 Predictions for $p+$Pb Collisions at $\sqrt{s_{_{NN}}} = 5$ TeV: Comparison With Data

Predictions made in Albacete et al. [1] prior to the
LHC $p+$Pb run at $\sqrt{s_{_{NN}}} = 5$ TeV are
compared to the mostly final data from that run. Some predictions shown here have been updated by including the same experimental cuts as the data. Others are additions too late for the initial publication.Comparisons to the available charged hadron, quarkonium, jet and gauge boson production, presented in Ref. [2], will be discussed.

[1] J. Albacete et al., Int. J. Mod. Phys. E $\mathbf{22}$ (2013)
133007.

[2] J. Albacete et al., submitted to Int. J. Mod. Phys. E,
arXiv:1605.09479.

Speaker: Ramona Vogt (LLNL and UC Davis)

HP16_talk.pdf

27 Gluon bremsstrahlung and flow assymetry in pA collisions

Recent experimental results display strong flow assymetry in pA collisions at LHC energies, similarly to AA collisions. We investigate the origin of this phenomena theoretically, studying the feature of induced gluon bremsstrahlung in pA and AA collisions. In parallel we include the effect into a HIJING model, localizing the phenomena at the microscopical level, and analyse its influence in a Monte-Carlo calculation. The talk will display our conclusion.

Speaker: Peter Levai (Hungarian Academy of Sciences (HU))

4-LevaiP_Gluonbrehm_Wuhan_0924.pdf

28 Jet energy loss in small systems with finite-size effects and running coupling

In the LHC and RHIC experiments, strong collective behaviors are being observed in high multiplicity events
in p-p and p-A collisions suggesting that quark-gluon plasma can be created in such small systems.
In this work, we utilize an improved version of MARTINI to calculate the effect of QGP
on the jet energy loss in p-A collisions with the well-calibrated 3+1D hydrodynamics medium.
The two important improvements implemented in this version of MARTINI are the finite medium size effect as formulated by Caron-Huot and Gale [1],
and the running coupling effect as proposed by Young, Schenke, Jeon and Gale [2]. Since the system we are dealing with is small,
both of these improvements are critical.
In this work, we first present that this improved model provides better descriptions of the nuclear modification factor ($R_{AA}$) in Pb-Pb collisions at 2.76TeV. Then we show a systematic measurement of jet quenching in small systems can provide a strong evidence of QGP formation.
In addition, harmonic flows of energetic partons and rapidity dependence of $R_{pA}$ in several collision systems will be highlighted.

$[1]$ S. Caron-Huot and C. Gale, Phys. Rev. C82, 064902 (2010), arXiv:1006.2379

$[2]$ C. Young, B. Schenke, S. Jeon, and C. Gale, Nucl. Phys. A910-911, 494 (2013), arXiv:1209.5679

Speaker: Chanwook Park (McGill University)

5-Chanwook_Park_HardProbe2016.pdf

Parallel Session I: Heavy Flavor (I)

Convener: Steffen A. Bass (Duke University)

29 Measurement of $D^0$ Meson Production and Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR

Since the charm-quark mass is larger than the thermal scales of the medium created in heavy-­ion collisions at RHIC energies, charm quarks are believed to be mainly produced through the initial hard scatterings. Therefore, they experience the entire evolution of the hot and dense medium. Charm quarks are also expected to thermalize slower with the medium than light flavor quarks, which is sensitive to the transport properties of the medium. Thus the modification of $D^0$ meson transverse momentum spectrum in heavy-ion collisions and its azimuthal anisotropy can provide new insight to the properties of the hot nuclear medium and its evolution.

Recently, STAR has successfully installed and collected data with the Heavy Flavor Tracker, which, with the power of two layers of Monolithic Active Pixel Sensors (MAPS), achieves a pointing resolution of less than 50 $\mu m$ for kaons with momentum of 750 $MeV/c$. With this performance STAR is able to carry out high precision $D^0$ measurements in a wide momentum range.

In this presentation, we will report our latest studies of $D^0$ meson via topological reconstruction in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The production yield and nuclear modification factor for $D^0$ in central collisions, as well as its azimuthal anisotropy $(v_{2})$ in minimum bias collisions will be presented. We will also compare our results with theoretical calculations with different implementations of charm-medium interactions and medium evolution.

Speaker: Xie Guannan (LBNL/USTC)

GuannanX_DMesonHP16_V4.pdf

30 D meson v_n harmonics in PbPb collisions at 5.02 TeV with CMS

Because of their large mass, heavy quarks are produced primarily at early stages of heavy-ion collisions, and therefore experience the full evolution of the system and carry information about the extent of thermalization of the QGP. Azimuthal anisotropy parameters (v_n) of charm and bottom hadrons provide unique information about the path length dependent interactions between heavy quarks and the medium. To what extent heavy quarks at low p_T flow with the medium is a good measure of the interaction strength. At high p_T, v_2 and v_3 from path length dependent energy loss provide a powerful tool to study heavy quark energy loss mechanisms. With the large PbPb data sample at 5.02 TeV collected by the CMS detector during the 2015 LHC run, azimuthal anisotropy v_2 and v_3 of D0 meson is measured over a wide p_T range and at different centralities. In this talk, new results of D0 meson v_n parameters are presented, and compared to the charged hadron v_n at the same energy and the latest theoretical calculations.

Speaker: Jian Sun (Purdue University (US))

HardProbes2016_D0vn_jiansun_v3.pdf

31 Heavy vs. light hadron production and medium modification at RHIC and LHC

Hard hadrons, including heavy flavor and high $p_\mathrm{T}$ light flavor hadrons, are ideal probes of the transport properties of the QGP matter created in relativistic heavy-ion collisions. We have established a Linearized Boltzmann Transport (LBT) model coupled with hydrodynamical background to study the in-medium evolution of hard partons, in which both elastic and inelastic processes are included and the interactions of heavy and light flavor partons with the QGP are treated in the same footing. Our LBT model naturally incorporates the temperature and energy dependences of parton-medium interaction, and therefore simultaneously describe heavy and light flavor hadron suppression for all centrality bins and all collision energies as observed from RHIC to LHC experiments. Within this framework, we have quantitatively extracted the temperature and momentum dependences of the jet transport coefficient $\hat{q}$ which are consistent with the range previously constrained by the JET Collaboration. In addition, the following flavor hierarchies of jet quenching have been demonstrated based on our calculation: $R_\mathrm{AA}^g < R_\mathrm{AA}^{q} < R_\mathrm{AA}^c$ for partons and $R_\mathrm{AA}^{h(g)} < R_\mathrm{AA}^{h({g+q})} < R_\mathrm{AA}^{D} < R_\mathrm{AA}^{h(q)}$ for hadrons.

Speaker: Shanshan Cao (Lawrence Berkeley National Lab)

HP 2016.pdf

HP 2016.pptx

32 Heavy flavor $R_{AA}$ and $v_n$ in event-by-event viscous relativistic hydrodynamics

Event-by-event fluctuations play a key role in resolving the long-standing $v_2$ to $R_{AA}$ puzzle for jets [1]. In this talk, the same general idea employed in [1] is used to investigate the event-by-event properties of $R_{AA}$ and $v_n$ of heavy flavor. Heavy quarks propagate and lose energy in the medium described by the 2D+1 viscous hydrodynamic code v-USPhydro [3] on an event-by-event basis, which allows for the first calculation of high $p_T$ elliptic flow cumulants $v_2\{2\}$, $v_2\{4\}$, $v_2\{6\}$, $v_2\{8\}$ for heavy flavor (and non-photonic electrons). We find that heavy flavor $v_2\{4\}=v_2\{6\}=v_2\{8\}$ at high $pT$, a strong indication that there is collectivity in the heavy flavor sector. We present predictions for heavy flavor $v_3\{2\}$ at LHC and discuss how event engineering in the soft sector [1] can be used to find the path length dependence of heavy quarks in the medium in highly anisotropic events.

REFERENCES:

[1] J.~Noronha-Hostler, B.~Betz, J.~Noronha and M.~Gyulassy,
Phys.\ Rev.\ Lett.\ {\bf 116}, 252301 (2016).

[2] J.~Noronha-Hostler, G.~S.~Denicol, J.~Noronha, R.~P.~G.~Andrade and F.~Grassi,
Phys.\ Rev.\ C {\bf 88}, 044916 (2013); J.~Noronha-Hostler, J.~Noronha and F.~Grassi,
Phys.\ Rev.\ C {\bf 90}, no. 3, 034907 (2014).

Speaker: Jorge Noronha (University of Sao Paulo)

Noronha_hard_probes_2016.pdf

33 Studies of the difference between light and heavy flavor energy loss by reconstructed jets

While the nuclear modification factor $R_{\rm AA}$ of charged hadrons measures jet quenching in terms of the suppression of single inclusive particle spectra, studies employing reconstructed jets additionally allow the investigation of medium modifications to the initial parton shower as a whole and thereby provide information about the angular dependence of jet quenching. Furthermore, due to mass effects the energy loss of jets is expected to be sensitive to the flavor of the shower-initiating parton. For investigating the medium modification of parton showers, we employ the transport approach BAMPS, which numerically solves the (3+1)D Boltzmann equation for gluons, light and heavy quarks based on pQCD cross sections for both 2$\rightarrow$2 and 2$\leftrightarrow$3 processes. While employing an improved Gunion-Bertsch matrix element together with a running coupling, BAMPS simulations show a good agreement with data for both $R_{\rm AA}$ and the elliptic flow $v_2$. We present recent results about the $R_{\rm AA}$ of inclusive and b-tagged reconstructed jets and the modification of the underlying jet shapes. We show that the suppression of b-tagged jets is dominated by elastic energy loss of the bottom quark, while radiative processes of gluons and light quarks additionally broaden the distribution of momentum within the inclusive jets.

Speaker: Zhe Xu

HP2016_v3.pdf

Parallel Session I: Jet Modification in A+A (I)

Convener: Rainer Fries (Texas A&M University)

34 Event-by-event picture for the medium-induced jet evolution

We discuss the evolution of an energetic jet which propagates through a dense quark-gluon plasma and radiates gluons due to its interactions with the medium. Within perturbative QCD, this evolution can be described as a stochastic branching process, that we have managed to solve exactly.
We present exact, analytic, results for the gluon spectrum (the average gluon distribution) and for the higher n-point functions, which describe correlations and fluctuations. Using these results, we construct the event-by-event picture of the gluon distribution produced via medium-induced gluon branching. In contrast to what happens in a usual QCD cascade in vacuum, the medium-induced branchings are quasi-democratic, with offspring gluons carrying sizable fractions of the energy of their parent parton. We find large fluctuations in the energy loss and in the multiplicity of soft gluons.
The multiplicity distribution is predicted to exhibit KNO (Koba-Nielsen-Olesen) scaling. These predictions can be tested in Pb+Pb collisions at the LHC, via event-by-event measurements of the di-jet asymmetry.

Based on e-Print: arXiv:1601.03629 [hep-ph] published in JHEP 1605 (2016) 008 and work in progress.

Speaker: Miguel angel ESCOBEDO ESPINOSA (CNRS)

1-1-jet_escobedo.pdf

35 Evolution of the jet opening angle distribution in holographic plasma

In this talk I will argue that essential progress can be made by studying the interplay of jet energy loss and the evolution of the jet opening angle as the jet traverses (strongly coupled) quark-gluon plasma. I will illustrate this evolution in a simple holographic model, where we start with energy and angular distributions from pQCD. We identify two competing effects: (1) all individual jets become wider, and (2) the distribution of final jets becomes narrower, since jets with a narrow opening angle suffer less energy loss and are thereby more likely to survive. Even though every jet widens, jets with a given energy can therefore have a smaller mean opening angle after passage through the plasma than jets with that energy would have had in vacuum, as experimental data may indicate.

Reference: Physical Review Letters 116, 211603 (2016)

Speaker: Wilke van der Schee (MIT)

1-2-wilke_Talk_Wuhan2.pdf

1-2-wilke_Talk_Wuhan2.pptx

36 Energy versus centrality dependence of the jet quenching parameter $\hat q$ at RHIC and LHC: a new puzzle?

We present here an extraction of the $\hat q$ parameter using data of inclusive particle suppression at RHIC and LHC energies for different centralities. Our approach consists of fitting a $K$ factor that quantifies the departure of this parameter from an ideal estimate, $K\equiv \hat q/(2\epsilon^{3/4})$, where $\hat q$ is determined by the local medium quantities as provided by hydrodynamical calculations. We find that this $K$ factor is larger at RHIC than at the LHC, as obtained already in previous analyses, but, surprisingly, it is almost independent of the centrality of the collision. Taken at face value, the $K$ factor would not depend on the local properties of the medium as energy density or temperature, but on global collision quantities such as the center of mass energy. This is a very intriguing, unexpected possibility for which we cannot yet provide a clear interpretation. This talk is based on arXiv:1606.14837

Speaker: Carlota Andres Casas

1-3-HP16_Carlota.pdf

37 Measurement of Inclusive Charged Jet Production in pp and Pb-Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV with ALICE

The LHC heavy-ion physics programme aims at investigating the fundamental properties of nuclear matter under extreme conditions of energy density and temperature, where a transition to a Quark-Gluon Plasma (QGP) is expected. Jets are now considered as established probes of the QGP due to their substantial energy loss while traversing the medium, resulting in a modification of their transverse momentum spectrum. To study nuclear effects on jet production, the ratio of the Pb-Pb jet transverse momentum spectrum divided by the pp reference, the so-called nuclear modification factor, is measured.
We will present measurements of inclusive charged jet production in Pb-Pb at the highest centre- of-mass energy of 5.02 TeV, and compare to the newly measured charged jet results in pp at the same beam energy, based on data samples collected with ALICE at the LHC in 2015.

Speaker: Hiroki Yokoyama (University of Tsukuba (JP))

1-4-20160924_HP2016_hiroki _v3.pdf

38 Hard Probe Measurements in Cu+Au Collisions at PHENIX: Jets and Leading Particles

Cu+Au collisions provide a unique system to study hard probes. For example,
the collision geometry at a fixed centrality is necessarily different from
that of symmetric Cu+Cu and Au+Au collisions. A systematic study of the
production of high-pT particles and jets in systems with different geometry
may provide information about the path-length dependence of energy loss in
the medium. The PHENIX experiment has measured the pT distributions and the
nuclear modification factors, R_CuAu, of jets and leading particles, such
as pi0, in Cu+Au collisions at 200 GeV. The jets are reconstructed with the
anti-kt clustering algorithm with a distance parameter of R=0.2, chosen to
minimize the contribution of the underlying event. The R_CuAu measurements
will be presented as a function of pT and centrality and compared to
theoretical calculations.

Speaker: Sergey Zharko (St. Petersburg State Polytechnic University)

1-5-HP2016_Zharko.pdf

10:10 Break

Parallel Session II: EM Probes (II)

Convener: Lijuan Ruan

39 Viscous corrections to photon production channels in QGP

Photons radiated in heavy-ion collisions are a penetrating probe, and as such can play an important role in the determination of the quark-gluon plasma (QGP) transport coefficients. In the first part of the talk we will present a calculation of the bulk viscous correction to photon production through two-to-two scattering, complementing a previous study involving the shear viscosity [1]. The presence of the bulk viscosity of QCD is now understood to be demanded by heavy-ion data [2]. In this work, phase-space integrals describing the bulk viscous correction are evaluated explicitly in order to avoid the forward scattering approximation which is shown to be poor for photons at lower energies. Furthermore, thermal masses are included in momentum distribution functions. We will present hydrodynamical simulations of AA collisions focusing on the effect of this calculation on photonic observables. In the second part, we will highlight the work done to calculate the viscous correction to other leading-order photon production mechanisms, such as bremsstrahlung, inelastic pair annihilation and the Landau-Pomeranchuk-Migdal effect. These had previously been shown to be as important as two-to-two scattering for QGP in equilibrium [3], while a viscous correction was still lacking. The equilibrium derivation used the Kubo-Martin-Schwinger (KMS) condition in a power counting scheme. Using more general arguments, we will show that in the viscous case only ladder diagrams with soft gluon rungs contribute at leading order to the photon self energy. Relevant phenomenological implications will be discussed.

[1] C. Shen et. al., Phys. Rev. C 91 no. 1, 014908 (2015).

[2] S. Ryu et. al., Phys. Rev. Lett. 115 no. 13, 132301 (2015).

[3] P. Arnold et. al., JHEP 2001 no. 12, 009 (2001).

Speaker: Sigtryggur Hauksson (McGill University)

presentation_sigtryggur_hauksson.pdf

40 Non-thermal photons in the quark-gluon plasma induced from jets

We investigate photon production in the non-equilibrium partonic transport approach BAMPS (Boltzmann Approach to Multi-Parton Scatterings). BAMPS serves as a microscopic tool to study expanding fireballs, employing a stochastic method to solve the relativistic 3+1d Boltzmann equation for quarks, gluons, photons and dileptons. The algorithm is able to closely reproduce the leading order photon production rate (AMY) in thermal equilibrium, using elastic and radiative microscopic scattering processes. BAMPS is applicable for the whole evolution of the quark-gluon plasma (QGP) in RHIC and LHC heavy-ion collisions, where the photon production is influenced by the chemical and thermal non-equilibrium of the early phase. Highly energetic quark- and gluon jets will convert into or radiate photons, effects we include by default.
We show results for photon spectra from the QGP and investigate its role for the elliptic flow of photons. Photons induced by jet-like particles show very different momentum anisotropies compared to the radiating bulk.
Dilepton contributions from the QGP are studied in a similar fashion.

Speaker: Moritz Greif (University of Frankfurt)

HP16_Moritz_Greif_talk.pdf

41 Holographic photon production and flow in strongly coupled quark gluon plasmas

We investigate the thermal-photon emission from strongly coupled gauge theories at finite temperature via the bottom-up models in holographic QCD in the deconfined phase. Particularly, we apply a model encoding flavor degrees of freedom in the Veneziano limit of a large number of colors $N_c$ and flavors $N_f$ but fixed $x=N_f=N_c$ (VQCD). In this model, the normalization and gauge-field couplings pertinent to photon production have been chosen to approximately reproduce the electric conductivity obtained from lattice simulations for the quark gluon plasma (QGP). The emission rates are then embedded in hydrodynamic simulations combined with prompt photons from hard scattering and the thermal photons from hadron gas to analyze the spectra and anisotropic flow of direct photons in RHIC and LHC. We compare the results for different sources responsible for the thermal photons in QGP including the weakly coupled QGP (wQGP) with hard-thermal-loop resummation, strongly coupled $\mathcal{N}=4$ super Yang-Mills (SYM) plasma (as a benchmark for reference), and Gubser’s phenomenological model in holography. In general, the direct-photon spectra are enhanced in the strongly coupled scenario compared with the ones in the wQGP especially in high momenta. Moreover, by using IP-glassma initial states, both the elliptic flow and triangular flow of direct photons are amplified in high momenta for VQCD and the SYM plasma as comparable with those for the wQCD, while the flow for VQCD is suppressed in low momenta, which is associated with the increase of electric conductivity with temperature. We further compare our results with experimental observations.

Speaker: Di-Lun Yang (RIKEN)

Hard_probes_2016.pdf

42 Low mass dielectron measurements in pp, p--Pb and Pb--Pb collisions with ALICE at the LHC

Low mass dielectrons are important probes of the hot and dense QCD medium created in heavy-ion collisions, since the production of low mass dielectrons is sensitive to
the thermodynamical properties of the medium and chiral symmetry restoration in the medium.

The ALICE experiment at the LHC has measured low mass dielectrons in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV to study and disentangle effects due to the cold nuclear matter. Recently, ALICE also measured low mass dielectron mass spectra for different pair $p_{\rm T}$ ranges in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV for the study of the
properties of the hot and dense medium.

In this talk, we will present the status of low-mass dielectron measurements in all collisions systems produced at the LHC and we will discuss the comparison with the
expected hadronic sources, the production of virtual photons in pp and Pb-Pb collisions, and the production of heavy-flavors in pp and p-Pb collisions. Future prospects of the low-mass dielectron measurements in ALICE at the LHC Run3 and Run4 will be discussed as well.

Speaker: Taku Gunji (University of Tokyo (JP))

gunji_hp2016_v2.pdf

43 Low-mass electron pairs from Au+Au collisions at 1.23A GeV with HADES

Lepton pairs are considered as ideal probe to access the microscopic properties of strongly-interacting matter under extreme conditions of temperature and density. The spectral distribution of lepton pairs in the region below the low mass vector mesons is characterized by an excess radiation above contributions from late meson decays (cocktail). It is theoretically well understood as a thermal radiation based on Vector Meson Dominance assuming a strong broadening of the in-medium $\rho$ spectral function due to coupling to baryons and anti-baryons.

In continuation of a systematic investigation of the emissivity of strongly interacting matter, HADES has recently measured the dielectron emission in Au+Au collisions at 1.23A GeV beam energy. The first measurement for Au+Au completes the systematics of dilepton production in NN/pA/AA collisions in the SIS18 energy range.

This contribution will present new results for the Au+Au system based on a data sample of 5.0 billion events of the 40% most central collisions. Data are presented for four centrality bins and include also double-differential spectra like e.g. transverse momentum distributions for different invariant mass bins. The data will be confronted with available model calculations. The integrated excess yield will be put in context of the dilepton excitation function measured in the RHIC beam energy scan.

Speaker: Patrick Sellheim (GSI)

PSellheim_HardProbes.pdf

Parallel Session II: Hard Probes in p+p and p+A Collisoions (II)

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

44 Jet transverse fragmentation momentum from h-h correlations in pp and p-Pb collisions

QCD color coherence phenomena, like angular ordering, can be studied by looking at jet fragmentation. As the jet is fragmenting, it is expected to go through two different phases. First, there is QCD branching that is calculable in perturbative QCD. Next, the produced partons hadronize in an non-perturbative way in a hadronization process. The jet fragmentation can be efficiently studied using the method of two particle correlations. A useful observable is the jet transverse fragmentation momentum $j_{\rm T}$, which describes the angular width of the jet. Previously for example the CCOR and PHENIX collaborations have measured $\sqrt{\left< j_{\rm T}^2\right>}$ in pp collisions and they have found no dependence on trigger $p_{\rm T}$. These results have been interpreted to reflect a universality in the jet hadronization process. However, they determine only a single value for $j_{\rm T}$ and therefore mix the two processes mentioned above. In this contribution, a more differential study will be presented in which separate $j_{\rm T}$ components for branching and hadronization will be distinguished from the data measured by the ALICE experiment. The $p_{\rm Tt}$ dependence of the hadronization component $\sqrt{\left< j_{\rm T}^2\right>}$ is found to be rather flat, as suggested by previous measurements. However, the branching component shows slightly rising trend in $p_{\rm Tt}$. The data from $\sqrt{s}=7~\text{TeV}$ pp and $\sqrt{s_{\rm NN}}=5.02~\text{TeV}$ p-Pb collisions will also be compared to the results obtained from PYTHIA8 simulations.

Speaker: Jussi Viinikainen (University of Jyvaskyla (FI))

jussi_jt_HardProbes2016.pdf

45 Jet and Leading Hadron Production in d+Au Collisions in the PHENIX Experiment

PHENIX has measured jet yields in p+p and d+Au collisions at 200 GeV [1].
In minimum bias collisions, the nuclear modification factor R_dAu is
consistent with unity. However, in centrality selected events R_dAu
exibits large pT-dependent deviations from unity, challenging
conventional models that relate hard-process rates and soft-particle
productin in nuclear collisions. Comparison of jet production and
high pT pi0 production in small system can shed light on the
surprising centrality dependence of jets. We will present the jet
results and the latest status of the comparison with pi0 production.

Reference
[1] A. Adare et al., Physical Review Letters 116, 122301 (2016)

Speaker: Takao Sakaguchi (BNL)

Sakaguchi_dpAu_HP2016_v3.pdf

46 Single inclusive forward hadron production at next-to-leading order

We discuss single inclusive hadron production from a high energy quark scattering off a strong target color field in the Color Glass Condensate formalism. Recent calculations of this process at the next-to-leading order accuracy have led to negative cross sections at large transverse momenta. We identify the origin of this problem as an oversubtraction of the rapidity divergence into the Balitsky-Kovchegov evolution equation for the target. We propose a new way to implement the kinematical restriction on the emitted gluons to overcome this difficulty.

Speaker: Yan Zhu (University of Jyvaskyla)

Zhu_nlosinc.pdf

47 Including resummation in the NLO BK equation

We include a resummation of large transverse momentum logarithms into the next-to-leading order Balitsky-Kovchegov equation. The resummed NLO evolution equation is shown to be stable, the evolution speed being significantly reduced by higher order corrections. The contributions from alpha_s^2 terms that are not enhanced by large logarithms are found to be numerically important close to phenomenologically relevant initial conditions. We numerically determine the value for the constant in the resummed logarithm that includes a maximal part of the full NLO terms in the resummation.

Speaker: Tuomas Lappi (University of Jyvaskyla)

hp16.pdf

48 Forward $J/\psi$ and D-meson production in pA collisions at the LHC

Inclusive production of $J/\psi$ mesons at forward rapidity can be an important probe of saturation dynamics. We study this process in the Color Glass Condensate framework, in which a large x gluon from the proton probe splits into a quark pair and eikonally interacts with the target proton or nucleus probed at small x. We show that relying on the optical Glauber model to obtain the dipole cross section of the nucleus from the one of the proton fitted to HERA DIS data leads to a smaller nuclear suppression than in the first study of this process in this formalism and a better agreement with experimental data. We then study the centrality dependence of our model and extend our calculation to backward rapidities using nuclear parton distribution functions. Finally, by integrating over the phase space of one of the produced quarks and convoluting with fragmentation functions, we study the consequences for the nuclear modification of forward D-meson production in the same kinematics.

Speaker: Bertrand Ducloue (University of Jyvaskyla)

Ducloue_HP2016.pdf

Parallel Session II: Heavy Flavor (II)

Convener: Qun Wang (University of Science and Technology of China)

49 B meson nuclear modification factor in PbPb at 5.02 TeV with CMS

The study of beauty production in heavy-ion collisions is considered one of the key measurement to address the flavour-dependence of in-medium energy loss in PbPb collisions. In pPb collisions, studies of b-quark production can also provide insights into the relevance of cold nuclear matter effects in the heavy-flavour sector. The CMS experiment has excellent capabilities for measuring b-quark production thanks to the excellent performances of its muon and tracker system. In this talk, we will present the measurement of nuclear modification factors for fully reconstructed B mesons in pPb, and for the first time, pp and PbPb collisions at 5.02 TeV, as a function of transverse momentum.

Speaker: Ta-Wei Wang (Massachusetts Inst. of Technology (US))

20160924_tawei_HP2016.pdf

50 Nuclear Modification of B mesons in Cu+Au Collisions at 200 GeV measured through the B-> J/Psi decay by the PHENIX Experiment

Because of their large mass, b quarks are expected to lose less energy
through qluon radiation than lighter quarks. This effect is most
pronounced for p_T << m_q. J/psi production from the B->J/psi decay
is a powerful observable to measure the nuclear modification of B
mesons in this p_T range. PHENIX has measured the yield of these
non-prompt J/psi's in Cu+Au collisions at 200 GeV at forward and
backward rapidity. This measurement was enabled by identifying the
secondary vertex of the B meson decay with the Forward Silicon Vertex
Detector (FVTX). The Cu+Au system studied is particularly interesting
due to the different admixtures of hot and cold nuclear matter effects
in the Cu- and Au-going directions.

Speaker: Cesar Luiz da Silva (Los Alamos National Lab)

Cesar_HardProbes_2016.pdf

51 AdS/CFT predictions for azimuthal and momentum correlations of bbbar pairs in heavy ion collisions

In arxiv:1305.3823v2, the azimuthal correlations of heavy $q\bar{q}$ pairs in a weakly coupled plasma in Pb+Pb collisions ($\sqrt{s}=2.76\text{TeV}$) were studied, both for a model involving purely collisional energy loss and one additionally incorporating radiative corrections.
These weak coupling based azimuthal correlations provide a secondary indicator for the momentum correlations and we compare them with computations from an AdS/CFT correspondence exploiting energy loss model sensitive to thermal fluctuations, the latter already having been introduced in arxiv:1501.04693.
As in arxiv:1501.04693, we probe the spectrum of reasonable AdS/CFT based energy loss models with two plausible 't Hooft coupling constants ($\lambda_1 = 5.5$ & $\lambda_2=12\pi\alpha_s\approx11.3$ with $\alpha_s=0.3$) with the additional requirements that, for the former, temperature and the Yang-Mills coupling are equated, while in the latter case, energy density and the coupling are equated.
The calculations are performed for the same transverse momentum classes as in arxiv:1305.3823v2 and also both with leading order and next-to-leading order production processes used for the initialisation.
Additionally, we consider momentum correlations that take initial momentum correlations into account.

When restricted to leading order production processes, we find that the strongly coupled correlations of high transverse momentum pairs ($>4\text{GeV}$) are broadened less efficiently than the corresponding weak coupling based correlations, while low transverse momentum pairs (1-4GeV) are broaded with similar efficiency, but with an order of magnitude more particles ending up in this momentum class. The strong coupling momentum correlations we compute account for initial correlations and reveal that the particle pairs suppressed from intially high momenta to the low momentum domain do not suffice to explain the stark difference to the weak coupling results in momentum correlations for 1-4GeV.
From this, we conclude that heavy quark pairs are more likely to stay correlated in momentum when propagating through a strongly coupled plasma than a weakly coupled one.

The next-to-leading order initialisation is performed using the aMC@NLO framework with Herwig++ as the event generator. Compared with the leading order initialisation, we observe significant broadening of the azimuthal correlations, and they are almost entirely washed out for low momentum pairs (1-4GeV).

Speaker: Robert Hambrock (University of Cape Town)

AdS:CFT predictions for azimuthal and momentum correlations of bbbar pairs in heavy ion collisions.pptx

52 Higgs boson and top-quark in nuclear collisions

Top-quark, Higgs boson, heavy-ions

Speaker: David d'Enterria (CERN)

dde_top_higgs_HP16_WuHan.pdf

53 Boosted tops and the time-structure of the hot dense-medium of heavy-ion collisions

Boosted top quarks have the potential to open up a new dimension in jet quenching studies. Because a top-quark’s decay time is correlated with its pt, by examining properties of jets from top-quark and W decays, as a function of the top-quark pt, one may obtain unique insight into the time dimension of the production and evolution of the quark-gluon plasma. Significant high-pt statistics are needed so this is of particular interest at future hadronic colliders being studied in China and Europe, where the top reconstruction will require the use of jet substructure techniques. However, the effects are not limited to these future machines, but accessible, to some extent, also at the LHC.

With a good control over the time evolution of the medium properties measured by jets, the ideas presented here may also open the door to using heavy-ion collisions one day to determine the properties of hadronically decaying new particles, providing a novel way to place constraints on their lifetime.

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

2-5-hCSalgadoHP2016.pdf

Parallel Session II: Jet Modification in A+A (II)

Convener: Ben-Wei Zhang (Central China Normal University)

54 Jet mass measurements in Pb--Pb and pPb collisions with ALICE at the LHC

The properties of the quark-gluon plasma (QGP) produced in high-energy heavy-ion collisions can be studied using high-momentum partons originating from the early stage of the collision. Their interaction with the medium provides information on the QGP properties.

High-momentum partons shower and hadronise into jets and the energy and mass of the jets are correlated to the energy and off-shellness (virtuality) of the original partons. The jet measurements hence allow us direct access to the virtuality evolution of the parton as a function of the jet energy. While propagating through the medium, the leading parton looses energy, leading to a suppression to the jet-$p_T$ spectrum, and virtuality.

The first measurements of the jet mass in Pb—Pb collisions at $\sqrt{s}_{NN} = 2.76$ TeV and pPb collisions at $\sqrt{s} = 5.02$ TeV at the LHC, performed with the ALICE experiment, are reported in the $p_{T,jet}$ region from 60 to 120 GeV/c. Jets were reconstructed using charged tracks with $p_T > 0.150$ GeV/c, clustered with the anti-$k_T$ algorithm, and fully corrected for background and detector effects. The Pb-Pb measurement is compared with the results from p-Pb collisions, with PYTHIA, and with models that implement different types of interactions with the medium that produce either a depletion or an increase of the jet mass.

These jet mass measurements add a new dimension to jet quenching studies, by constraining both of the relevant quantities, energy and virtuality, and will further provide non-trivial tests for models of in-medium shower evolution.

Speaker: Chiara Bianchin (Wayne State University (US))

amendmentModels.pdf

jetmassPbPbpPbALICEFinal.pdf

55 Measurement of jet internal structure in p+p, p+Pb, and Pb+Pb collisions with the ATLAS detector

In Pb+Pb collisions at the LHC hot QCD matter, the quark-gluon plasma (QGP), is produced. One way to study this matter is by using QCD jets as probes. The rates of these jets have been found to be reduced over a wide kinematic range due to the loss of some of the jet’s energy outside the jet cone. It is of great interest to have information on how the momentum of these jets is distributed to the particles inside the jet in order to gain understanding about the energy loss process. The longitudinal momentum fraction of charged particles in Pb+Pb, p+Pb, and p+p collisions have been measured by the ATLAS collaboration. Proton-proton and p+Pb collisions provide baseline measurements for the modifications in Pb+Pb collisions. In addition, p+Pb collisions should help to constrain the magnitude of nuclear modifications of parton distribution functions as well as to quantify a potential contribution of these modifications to the modifications of the jet fragmentation seen in Pb+Pb collisions. In 2015 a large sample of p+p collisions at 5.02 TeV were collected. This data provides a reference for the p+Pb fragmentation functions at the same collision energy. In this talk, we will present updated results on Pb+Pb fragmentation functions at 2.76 TeV and p+p and p+Pb fragmentation function measurements at 5.02 TeV.

Speaker: Martin Rybar (Univ. Illinois at Urbana-Champaign (US))

HP2016_Rybar.pdf

56 Calculating the Jet quenching parameter in quenched SU(3) lattice gauge theory

We investigate the jet quenching parameter $\hat{q}$ using quenched SU(3) lattice gauge theory at finite temperature.
A first-principles calculation of the jet quenching parameter is performed by a combination of perturbative and
nonperturbative methods based on Ref.[1]. Focusing on the simplest process of jet broadening at leading order in the medium,
we carry out an operator product expansion of the nonperturbative operator product in the deep Euclidean region of momentum space and relate it to the expectation
of operators in the physical region though dispersion relations. The expectation value of the ensuing local operators is calculated on a quenched SU(3) lattice.
We will present results for both the leading term, and next-to-leading power corrections to the operator product that represents $\hat{q}$ as a function of temperature and lattice spacing.
We will also discuss the corrections to these which originate from higher derivative terms.

[1] A.Majumder, Phys. Rev. C87, 034905 (2013)

Speaker: Chiho Nonaka (Nagoya University)

2-3-nonaka_hp.pdf

57 Factorization of in-medium parton branching beyond the eikonal approximation

The description of the in-medium modifications of parton showers is at the forefront of current theoretical and experimental efforts. The theory of jet quenching, a commonly used alias for the modifications of QCD parton branching resulting from the interactions with the QGP, has been significantly developed over the last years. Within a weak coupling approach, several elementary processes that build up the parton shower evolution such as single gluon emissions, interference effects between successive emissions and corrections to radiative energy loss off massive quarks, have been addressed both at eikonal accuracy and beyond by taking into account the Brownian motion that high-energy particles experience when traversing a hot and dense medium. In this work, using the setup of single gluon emission from a color correlated quark-antiquark pair in a singlet state (a q-qbar antenna), we calculate the in-medium gluon radiation spectrum beyond the eikonal approximation. This allows us to fully explore the physical interplay between broadening and coherence/decoherence effects. The results show factorization of broadening effects from the modifications of the radiation process itself in the limit of soft emissions. As such, we show that a probabilistic picture of in-medium parton shower evolution holds beyond eikonal accuracy, a feature that is of the utmost importance for a successful future generation of jet quenching Monte Carlos.

Speaker: Liliana Apolinario (Instituto Superior Tecnico (PT))

2-4-Liliana_HP16.pdf

58 Jet and Heavy Flavor Production from Soft Collinear Effective Theory

One of the earliest phases of our universe, the quark-gluon plasma (QGP), can be reproduced in heavy-ion collisions at RHIC and the LHC. Rare high energy probes produced in these collisions that traverse the hot and dense QCD medium, provide an excellent tool to probe this state of matter. In particular, the medium modification of jet and heavy flavor production cross sections has received a growing attention in recent years. We consider the nuclear modification factor $R_{AA}$ which is most commonly used to study the quenching of hadron or jet production yields in heavy-ion collisions. We present new theoretical calculations based on recently developed techniques using Soft Collinear Effective Theory (SCET). In particular, we have developed a new formalism to resum logarithms in the jet radius parameter $R$ for inclusive jet spectra. We present results for the medium modification of jet and heavy meson cross sections. In addition, we present new results for the modification of jet-substructure observables in heavy-ion collisions.

Speaker: Felix Ringer (Los Alamos National Laboratory)

Ringer_HP16.pdf

12:20 Lunch

Parallel Session III: EM Probes (III)

Convener: Axel Drees

59 Production of e$^{-}$e$^{+}$ from U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV and Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4, and 200 GeV as measured by STAR

Dileptons are able to traverse a strongly interacting medium with minimal interactions and thus are excellent probes of the hot, dense, and strongly interacting medium created in relativistic heavy-ion collisions. For the dileptons with an invariant mass less than ~1.2 GeV/c$^{2}$, the production is predominately from vector-meson decays. Information about any in-medium modifications of the vector meson is retained in its decay products, and may provide a possible link to chiral symmetry restoration. In addition, yields from the $\rho$-meson decays and the hot, dense partonic medium can be used as a measurement of the medium’s lifetime. STAR has systematically studied the dielectron invariant mass spectrum in the aforementioned region for a variety of centralities, system-sizes, and collision energies. This presentation will cover the dielectron continuum measurement as a function of centrality, invariant mass, and transverse momentum for U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV; the dielectron continuum measurement as a function of invariant mass for minimum-bias of Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, and 62.4 GeV; and the acceptance-corrected dielectron excess measurements of U+U collisions at $\sqrt{s_{NN}}$ = 193 and Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4, and 200 GeV collisions. The connection between the measured dielectron excess yield and the lifetime of the hot, dense medium will be discussed.

Speaker: Joey Butterworth (Rice University)

HardProbes2016_Butterworth_Uploaded.pdf

60 Measurement of W and Z boson production in 5 TeV pp, p+Pb and Pb+Pb collisions with the ATLAS detector

W and Z bosons are short lived and do not interact strongly. Thus their production yields, observed via dilepton decay channels in proton-lead and lead-lead collisions, provide direct tests of both binary collision scaling and the nuclear modification of parton distribution functions (nPDF). Proton-lead collisions further provide an excellent opportunity to test nPDFs. The ATLAS detector has a broad acceptance in the muon and electron channels, with excellent performance even in the high occupancy environment of central heavy-ion collisions. ATLAS has recorded 520 µb−1 of lead-lead data at the new center-of-mass energy of 5.02 TeV. Weak-boson production yields are expected to increase by a factor of eight relative to the available Run 1 data at 2.76TeV. In addition the data can be compared directly to the 29nb−1 of proton-lead data collected in Run 1. In this talk, W and Z boson production yields, and lepton charge asymmetries from W decays, are presented differentially in rapidity and transverse momentum as a function of centrality in lead-lead and proton-lead collisions.

Speaker: Mirta Dumancic (Weizmann Institute of Science (IL))

md_HP2016_WZ.pdf

61 Probing cold nuclear medium effect with $W^{\pm}/Z^0$ at NLO and NNLO in heavy-ion collisions

The production of massive vector boson ($W^{\pm}/Z^0$), is an excellent probe of the cold nuclear medium effect, and can provide useful constraints on the nuclear parton distribution (nPDFs), in heavy-ion collisions at the LHC and the future colliders with much higher energies.

Within the framework of perturbative QCD, we systematically study the vector boson production in p+Pb and Pb+Pb collisions at the LHC and future colliders at NLO and at NNLO. Theoretical predictions with parametrization nPDFs sets, EPS09 and DSSZ, give good descriptions of the recent data on boson rapidity and transverse momentum distributions at the LHC. Differences between the predictions with several nPDFs sets are observed, and a detailed analysis of nuclear modification at partonic level is performed.

Furthermore, with a semi-microscopic KP model of nPDFs, in which several nuclear effects (e.g. Fermi motion and nuclear binding, the off-shell correction, the nuclear coherent correction, and the nuclear meson correction) are included, we study the vector boson rapidity distribution in p+Pb collisions at the LHC, and a very good agreement with the latest data is found.

Speaker: Peng Ru (Dalian University of Technology)

Ru_WZ_HP2016_v3.pdf

62 Photon from the Color Glass Condensate in the pA collision

In this contribution I will talk about our recent results on photon production from the Color Glass Condensate (CGC) in the high energy pA collision. The nucleus is considered as a dense source of soft gluons while the proton is more dilute. This allows a systematic expansion of the amplitude in the powers of the gluon density of the proton.
The zeroth order approximation comes from bremsstrahlung of valence quarks in the proton and was originally calculated by Gelis and Jalilian-Marian (PRD D66 (2002) 014021). The first order corrections has two processes with the soft gluons in the proton emitting a quark-antiquark pair. In the first process the pair subsequently annihilates to a photon, while the second is of a bremsstrahlung type with the quark-antiquark pair and the photon in the final state.
The main results I will report on are:
1. The full analytic formula for the photon rate, that is, taking into account the annihilation as well as the bremsstrahlung process.
2. The numerical evaluation of the photon rate for the annihilation process by using the McLerran-Venugopalan model for the color average through which the rate becomes characterized by the saturation scale.
These results are partially contained in arXiv:1602.01989.

Speaker: Sanjin Benic (University of Tokyo)

1_4benic_wuhan2016.pdf

63 Photon production in the early stages of ultrarelativistic heavy ion collisions

We introduce a model for the early stages of ultrarelativistic heavy ion collisions, in which initial strong color fields decay to a quark-gluon plasma via the Schwinger mechanism; the dynamics of the coupled fields+plasma system is studied consistently by means of relativistic transport theory coupled to classical equations of motion for the fields. This model is useful to grasp important properties of the early time evolution of the quark-gluon plasma produced in heavy ion collisions, with particular reference to isotropization and thermalization, as well as to the particle production time and chemical composition of the plasma. We then use this model to discuss photon production in the early stages of the collision, with emphasis on photon multiplicity and spectrum, and compare the results obtained within a standard MC-Glauber initialization.

Speaker: Marco Ruggieri

1_5HP2016_V2.pdf

Parallel Session III: Heavy Flavor (III)

Convener: Xin Dong (Lawrence Berkeley National Lab)

64 $D_{s}^{\pm}$ meson production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR

Heavy quarks, predominantly produced in hard scattering processes at the initial stages of heavy-ion collisions, are considered excellent probes to the strongly interacting deconfined medium formed in these collisions. In particular the $D_{s}($c$\bar{s}/\bar{c}$s) production in heavy-ion collisions is expected to be affected by both the strangeness enhancement and the primordial charm quark production. Thus the modification of the $D_{s}$ meson spectra in heavy-ion collisions provides a new probe to study key properties of the hot nuclear medium.

The Heavy Flavor Tracker, installed at the STAR experiment since 2014, is designed to extend STAR's capability of measuring heavy flavor production via the topological reconstruction of displaced decay vertices. It provides a unique opportunity for precise measurement of the $D_{s}$ meson production in heavy-ion collisions at RHIC energies. We will present the measurement of $D_{s}$ meson production via the decay channel $D_{s}\rightarrow\phi(1020)+\pi$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Preliminary results on the nuclear modification factor ($R_{AA}$) and the production ratio $D_{s}/D^{0}$ will be presented.

Speaker: Long Zhou (USTC && BNL)

HP2016_LongZhou_v6.pdf

65 $D^0$ meson production in proton-lead and lead-lead collisions at $\sqrt{s_{NN}}$=5 TeV with LHCb

see abstract

Speaker: Xianglei Zhu (Tsinghua University (CN))

HP2016_LHCb_OpenCharm_v4.pdf

66 D meson nuclear modification factor in PbPb at 5.02 TeV with CMS

The measurement of heavy flavour production is a powerful tool to study the properties of the high-density QCD medium created in heavy-ion collisions as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. In particular, the comparison between the nuclear modification factors of light- and heavy-flavour particles provides insights into the expected flavour dependence of in-medium parton energy loss. Using the large statistics proton-proton and PbPb samples collected at 5.02 TeV during the 2015 LHC run, high precision open charm measurements are performed with the CMS detector in a wide transverse momentum range, from few GeV up to approximately 100 GeV. This allows us to set an important milestone in our understanding of energy loss phenomena. In this talk, the most recent results of nuclear modification factor of $D^{0}$ mesons in PbPb collisions at 5.02 TeV are presented and compared to the charged hadron nuclear modification factor at the same energy.

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

20160924_HP2016_JingWang_MIT_vFinal.pdf

67 Open Heavy Flavor dynamics: impact of T-dependent medium interaction and initial magnetic field

1) S.~K.~Das, F.~Scardina, S.~Plumari and V.~Greco,
``Toward a solution to the $R_{AA}$ and $v_2$ puzzle for heavy quarks,''
Phys. Lett. B747 (2015) 260

2) S.~K.~Das, F.~Scardina, S.~Plumari and V.~Greco,
``Heavy-flavor in-medium momentum evolution: Langevin versus Boltzmann approach,''
Phys. Rev. C90 (2014) 044901

3) S.~K.~Das, J.~M.~Torres-Rincon, L.~Tolos, F.~Scardina and V.~Greco,
``Propagation of heavy baryons in heavy-ion collisions. II: observables and predictions,'' arXiv:1604.05666 [nucl-th].

Speaker: Vincenzo Greco (University of Catania)

Greco-HP2016.pdf

68 Data-driven analysis of the temperature and momentum dependence of the heavy-quark transport coefficient

Heavy quarks (charm and bottom) serve as valuable probes to study the properties (such as the transport properties) of the strongly-interacting quark-gluon plasma created in ultra-relativistic heavy-ion collisions. However, the simultaneous description the nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of heavy quarks poses a significant challenge for most commonly used transport models, in particular those based on Langevin transport. We purpose a generalized ansatz for the temperature and momentum dependence of the heavy-quark diffusion coefficient and subsequently extract its functional form from a Bayesian model-to-data comparison. Using the results of this analysis, our improved Langevin framework is able to simultaneously reproduce the experimental data of $R_{AA}$ and $v_2$ , at both RHIC and the LHC energies.

The Bayesian analysis used to extract the information of transport properties of the QGP is set up as follow: a set of input parameters related to the transport coefficient $\hat{q}$ are evaluated via an event-by-event (ebe) heavy flavor dynamic model: heavy quarks propagate through the medium according to an improved Langevin equation, which incorporates both radiative and collisional energy loss in an ebe 2+1 dimensional viscous hydrodyncamical background. The hadronization of heavy quarks is described via a hybrid model of fragmentation and recombination. The calculations are used to train Gaussian process emulators that interpolate the full input parameters space and are capable of predicting the outcome of the dynamical model at any arbitrary point in parameter space. We then calibrate the model parameters on experimental data using Bayes Theorem through Markov chain Monte Carlo (MCMC) sampling. The final result of the analysis are the posterior distributions for all model parameters that contain the high likelihood ranges in which the model describes the data optimally. We find that the transport coefficient $\hat{q}$ has a maximum value around critical temperature, then rapidly decreases with increasing temperature. We also observe a non-trivial momentum dependence of the transport coefficient. With the extracted functional form of $\hat{q}$ (which can be related to the diffusion coeffecient), the $R_{AA}$ and $v_2$ of heavy quarks in different centralities at 200 GeV Au+Au collisions and 2.56 TeV Pb+Pb collisions are calculated, and observed to be consistent with the experimental data.

Speaker: Yingru Xu (Duke University)

Model_to_data_analysis_of_HQ.pdf

Parallel Session III: High pT Correlations (I)

Convener: Peter Levai (Hungarian Academy of Sciences (HU))

69 PHENIX results on direct photon-hadron correlations

The PHENIX experiment was designed to excel at measurements of photons.
Direct photons provide a unique tool for measuring jet energy loss, because
they do not participate in the strong interaction and do not lose energy in
the QGP. At leading order the photons are produced with an opposing quark
jet, and the measurement of the photon energy provides a calibrated way to
determine the amount of energy lost by the quark in the medium. Measurements
of direct photon-hadron correlations in p+p, d+Au and Au+Au collisions may
reveal possible modifications of the quark fragmentation in Au+Au collisions
due to interactions with the medium. This talk will present the most recent
PHENIX results using direct photon-triggered correlations and compare these
measurements to pi0-hadron correlations in the same collision systems.

Speaker: Huijun Ge (Stony Brook University)

1-1 HP2016_gamma_hadron_hge.pdf

70 Jet-induced medium excitation in heavy-ion collisions

The transport of jet shower partons and jet-induced medium excitations are investigated simultaneously within the coupled Linear Boltzmann Transport and hydro (CoLBT-hydro) model. In this coupled approach, the LBT model is coupled to 3+1D hydrodynamic model in real time with fluctuating initial conditions. The elastic collisions and radiation processes of energetic partons are simulated by LBT model with the background of the evolving bulk medium described by 3+1D hydrodynamic model. Energy and momentum of soft partons from LBT model are deposited into the medium via a source term in the 3+1D hydrodynamics. The hydro background for the LBT simulation is then updated for each time step. Using this CoLBT-hydro model, we simulate transport of gamma-jets and medium excitation in heavy-ion collisions. Hadron spectra from both the hadronization of jet shower partons and the medium excitation are calculated and compared to experimental data. Parton energy loss of jet shower partons leads to the suppression of hadron at large z_T=pTh/E_Tgamma while medium excitations leads to enhancement of hadrons at small z_T. We further calculate gamma-hadron angular correlation which shows significant broadening for low pt<2 GeV hadrons.

Speaker: Wei Chen (CCNU)

1-2-chenwei.pdf

71 Z-Jet Correlations in pp and PbPb collisions at 5.02 TeV with CMS

A typical approach to study the medium produced in heavy ion collisions is to understand the passage of elementary particles through it. As Z bosons do not participate in the strong interaction, Z+jet production is an important process for the study of the medium-induced energy loss of (predominantly) quark jets. Furthermore, unlike photons, Z bosons are not contaminated by background processes such as jet fragmentation and neutral meson decays, making Z+jet correlations a particularly powerful tool in energy loss studies. In this analysis, the first Z+jet correlation measurement using the high statistics PbPb and pp data taken at a center-of-mass energy of 5.02 TeV with the CMS in 2015 is reported, using both dielectron and dimuon Z decay channels. The evolution of azimuthal angular distributions and average momentum imbalance as a function of Z boson transverse momentum will be presented for 40 GeV/c < Z pT < 120 GeV/c.

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

160924_HP2016_KayaTatar.pdf

72 Effect of collisional energy loss on particle correlations in AMPT

Jet quenching is a powerful tool to study medium properties of relativistic heavy ion collisions via jet-medium interactions. Jet quenching studies have so far focused on high transverse momentum ($p_T$) particle suppression. Jet shapes at low to intermediate $p_T$, containing rich information on jet-medium interactions, have been less explored. Experimentally, jetlike correlations at low $p_T$ suffer from large uncertainties in anisotropic flow background. Recent development in data-driven flow subtraction will hopefully eliminate such uncertainties. Theoretically, jet shapes have been difficult to tackle due to non-perturbative effects at low $p_T$. In this talk, I will present a recent study, using a multiphase transport (AMPT) model, of effects on particle correlations from collisional energy loss of partons traversing the heavy ion medium. We follow the parton cascading history so that medium partons (associated particles) which have interacted with a high-$p_T$ probe parton (hard probe trigger particle) can be uniquely identified and hence no subtraction of combinatorial background is needed. Results on particle correlation shapes will be presented as a function of $p_T$, the number of parton-parton collisions suffered by the probe parton, and the azimuthal angle of the probe parton relative to the reaction plane. These results reveal pathlength dependence of collisional energy loss that I will discuss. Potentials and future prospects of such transport model studies and experimental data comparisons will be discussed.

Speaker: Fuqiang Wang (Purdue University (US))

fqwang_HP2016.pdf

fqwang_HP2016.pptx

73 Measurement of D-meson triggered correlations in p+p collisions at RHIC

Heavy-flavor triggered correlations offer a unique sensitivity to study QCD and the QCD medium created in high energy nucleus collisions. Measurement of heavy quark production in p+p collisions allows us to test perturbative QCD calculations and provides a reference for similar studies in heavy-ion collisions. Analysis of heavy-flavor triggered azimuthal correlations and comparisons to light hadron results can also provide insight into the differences in hadronization and interactions with the medium between heavy quarks and light quarks in these collisions.

Preliminary results of azimuthal correlations between D mesons and charged hadrons (D-h) measured by the STAR experiment in p+p collisions will be presented. Comparisons are made to light-hadron triggered correlations (h-h) and PYTHIA simulations. We will also present the measurement of azimuthal correlations between D and anit-D mesons (D-D) in p+p collisions. Furthermore, the prospects of heavy-flavor triggered correlation measurements in heavy-ion collisions will be discussed.

Speaker: Long Ma (Shanghai Institute of Applied Physics)

1-5-HP_talk_MaLong.pdf

Parallel Session III: Jet MC and Jet Modification in A+A

Convener: Joern Putschke (Yale University)

74 Angular Structure of Jet Quenching within a Hybrid Strong/Weak Coupling Model

Building upon the hybrid strong/weak coupling model for jet quenching, we incorporate the effects of transverse momentum broadening and contributions from the response of the plasma to the jet, aka the wake, and study their effects on a variety of observables. We find little sensitivity to the strength of broadening for inclusive observables. However, we propose new observables constructed from ratios of differential jet shapes, in which particles are binned in momentum, which are sensitive to the value of the in-medium broadening parameter. We also study dijet and boson-jet acoplanarities and find a generic narrowing of the angular distribution with respect to the vacuum due to energy loss. Finally, we investigate the effect of the backreaction of the medium on the angular structure of jets as reconstructed. We provide a detailed analysis of the so called "missing-pt", finding a qualitative agreement between our model calculations and data in many respects, as well as evidence that our simplified analysis of the hadrons originating from the wake in the plasma underproduces semihard particles.

Speaker: Daniel Pablos Alfonso (Barcelona University)

pablos_angularstructure.pdf

75 Advanced jet modification observables explored with Monte Carlo models

The highly increased quality and statistics of the experimental data on jet production in heavy-ion collisions, collected in recent years at RHIC and LHC, allow investigation well beyond that of jet suppression in terms of the nuclear modification factor. Of particular interest are multi-particle correlation observables that probe medium-induced modifications either in the trigger-recoil di-jet system or in intra-jet structure.

Utilizing available Monte Carlo models of jet quenching, such as YaJEM [1] and JEWEL [2], we explore novel strategies to study the in-medium modification of hard probes, and focus on jet-hadron correlations and jet substructure using the Soft Drop algorithm [3].

Studies of jet-hadron correlations with models are essential in order to understand the trigger properties, i.e. the correlation between the trigger jet and the corresponding hard parton, and the related issue of surface biased jets. We present studies of jet-hadron correlations and surface biases both at RHIC and LHC energies, compare results of different models, and discuss implications for the analysis and interpretation of experimental data.

Another promising approach to explore jet modification is to study the jet substructure. We assess the performance of the Soft Drop jet substructure algorithm in heavy ion collisions. Sensitivity of the algorithm to the possible medium-induced modification of the QCD splitting kernel will be discussed. Furthermore, the performance of the background subtraction techniques will be presented. These studies provide a necessary foundation and help to guide on-going data analysis efforts.

1. T. Renk, PRC 84 (2011) 067902.

2. K. Zapp et al. JHEP 1303 (2013) 080, EPJC C60 (2009) 617.

3. A. J. Larkoski, S. Marzani, G. Soyez, J. Thaler JHEP 05 (2014) 146.

4. A. J. Larkoski, S. Marzani, J. Thaler PRD 91, 111501(R).

Speaker: Kirill Lapidus (Yale University (US))

1-2-hard_probes_2016_lapidus_final.pdf

76 Reconstructed jets in a multiphase transport model

Several reconstructed-jet observables are simulated for Pb+Pb collisions at 2.76 TeV by using a multiphase transport (AMPT) model with a triggered dijet (or photon-jet), which provides a complete understanding of the dynamical evolution from jet energy loss in QGP, jet hadronization to jet transport in a hadronic matter. We find that the measured asymmetry of dijet is driven by both initial dijet asymmetry and final jet partonic energy loss. We show that the imbalance ratio of photon-jet is sensitive to both production position and passing direction of photon, which can be applied for a detail tomography on the QGP. The jet fragmentation function in Pb+Pb collisions is decomposed into two contributions from jet fragmentation and coalescence due to a competition between the two jet hadronization mechanisms. For jet shape, we propose that the sub-leading jet shape can display a larger medium modification effect than the leading jet because of its longer path-length inside the QGP. We also demonstrate that the path-length dependence of jet energy loss leads to azimuthal anisotropies of jets, which is very sensitive to the geometry fluctuations of initial partonic distribution.

Speaker: Guo-Liang Ma (Shanghai INstitute of Applied Physics (SINAP), CAS)

HP2016_Jet_MaGuoliang.pdf

77 Medium recoil in JEWEL

JEWEL is a fully dynamical event generator for jet evolution in a dense
QCD medium, which has been validated for multiple jet and jet-like
observables. Jet constituents (partons) undergo collisions with thermal
partons from the medium, leading to both elastic and radiative energy
loss. The recoiling medium scattering centres carry away energy and
momentum from the jet. Keeping track of these recoils is essential for
the description of intra-jet observables. Since the thermal component of
the recoils is part of the soft background activity, comparison with
data on jet observables requires the implementation of a background
subtraction procedure. We will show two independent procedures through
which background subtraction can be performed and discuss the impact of
the medium recoil on jet shape observables and jet-background
correlations. Keeping track of the medium recoil significantly improves
the JEWEL description of jet shape measurements.

Speaker: Raghav Kunnawalkam Elayavalli (Rutgers, State Univ. of New Jersey (US))

JEWEL_recoils_HP16Wuhan_raghav_v4.pdf

78 Baryon to meson ratio in jets and underlying event in Pb–Pb, p–Pb and pp collisions with ALICE detectors

It has been found that the baryon to meson ratio at intermediate transverse momentum ($p_{\rm T}$) is up to a factor two larger in the systems such as Pb-Pb but also p-Pb collisions than that in pp collisions. Particle production at intermediate $p_{\rm T}$ is expected to have contributions from hadronization of the medium as well as from fragmentation of high-momentum partons.
To disentangle the different contributions, ALICE studies particle production in reconstructed jets and the underlying event separately.

In this contribution, we present of the $p_{\rm T}$ spectra of $\Lambda$ ($\overline{\Lambda}$) baryons and ${\rm K}^0_{\rm S}$ mesons produced in association with charged jets in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV, p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and pp collisions at $\sqrt{s}=7$ TeV. The analysis is based on data recorded by ALICE at the LHC, exploiting its excellent particle identification capabilities. Features of baryon to meson ratios in jets at such collision systems will be explored. A comparison will be shown to the ratios obtained for inclusive particle production and for particles stemming from underlying event as well as to PYTHIA pp simulations.

Speaker: Yonghong Zhang (Central China Normal University CCNU (CN))

2016-Sep-23-conferencefile-20160924_HP_Yonghong_v2.pdf

15:40 Break

Parallel Session IV: Heavy Flavor (IV)

Convener: Hua Pei (Central China Normal University CCNU (CN))

79 Measurements of the suppression and anisotropy of heavy-flavour particles in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV with ALICE

Heavy quarks, i.e. charm and beauty, are formed on a shorter time scale with respect to the strongly-interacting matter produced in high-energy heavy-ion collisions. Therefore, they are sensitive probes to study the mechanisms of parton energy loss, hadronisation and thermalization in the hot and dense state of matter.

The heavy-flavour nuclear modification factor ($R_{\rm AA}$) and the elliptic flow ($v_{2}$) are two of the main experimental observables that allow us to investigate the interaction strength of heavy quarks with the expanding medium.
$R_{\rm AA}$ accounts for the modification of heavy-flavour hadron yields in Pb--Pb collisions with respect to pp collisions, after the proper binary collision scaling is applied on the latter system. The comparison of the $R_{\rm AA}$ of charm, beauty and light-flavour hadrons can provide information about the colour-charge and parton-mass dependence of the parton energy loss.
At low $p_{\rm{T}}$ the $v_{2}$ is expected to bring insights into the degree of thermalization of heavy quarks in the deconfined medium, and at high $p_{\rm{T}}$ it carries information on the path-length dependence of in-medium parton energy loss.

In this talk, the $R_{\rm AA}$ and the $v_{2}$ of open heavy-flavour hadrons via their hadronic and semi-leptonic decays to electrons at mid-rapidity and to muons at forward rapidity in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV will be discussed. Progress on the study of the $R_{\rm AA}$ of electrons from heavy-flavour and beauty-hadron decays will be also discussed. Comparisons with model calculations including the interaction of heavy quarks with the hot, dense, and deconfined medium will be discussed.

Speaker: Andrea Dubla (GSI)

HF_PbPb_HP16_ADubla.pdf

80 Measurement of the suppression and v_{n} of heavy flavor muons in lead-lead collisions with the ATLAS detector

ATLAS has measured the production of heavy flavor muons in 2.76 TeV pp and Pb+Pb collisions at the LHC. The measurements are performed over the transverse momentum range 4 < pT < 14 GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and mis-reconstructed muons are statistically removed using a template fitting procedure. The heavy flavor muon differential cross-sections and per-event yields are measured in pp and Pb+Pb collisions, respectively. The nuclear modification factor, RAA , is observed to be independent of pT within uncertainties and to be less than unity, which indicates suppressed production of heavy flavor muons in Pb+Pb collisions. The heavy flavor muon yield is measured as a function of the azimuthal angle difference, phi-Psi_{2}, where the experimental event plane angle, Psi_{2} is measured in forward calorimeters that cover 3.2 < |y| < 4.9. Fourier coefficients associated with the cos(2(phi-Psi_{2})) modulation, v2 , are measured as a function of pT and centrality. They vary slowly with pT and show a systematic variation with centrality that is characteristic of other elliptic anisotropy measurements. Higher harmonics v3 and v4 are also measured using Scalar Product method.

Speaker: Qipeng Hu (University of Science and Technology of China (CN))

QHU_HP2016_ATLASHF.pdf

81 Nonperturbative Approach to Open Heavy Flavor in Relativistic Heavy Ion Collisions

We evaluate open heavy-flavor (HF) transport in relativistic heavy-ion
collisions utilizing a strong-coupling treatment for both macro- and
micro-dynamics of the problem [1]. The former is realized through a
hydrodynamic evolution quantitatively constrained by bulk-hadron spectra
and elliptic flow. The HF transport is based on non-perturbative $T$-matrix
calculations of heavy-light parton scattering in the Quark-Gluon Plasma
(QGP) [2], yielding a diffusion coefficient consistent with lattice QCD,
and on effective interactions of $D$-mesons with light hadrons in hadronic
matter [3]. The $T$-matrix interactions in the QGP lead to resonance
formation close to $T_c$ which are implemented as a hadronization (recombination)
mechanism on a hydrodynamic hypersurface, providing a seamless treatment
of HF interactions throughout the bulk-medium evolution. We deploy this
framework for a comprehensive study of open HF observables from
62-2760 GeV [4,5,6]. A fair description of current experimental data for the
nuclear modification factor and elliptic flow of $D$, $D_s$, $B$ mesons and
HF leptons emerges at low and intermediate transverse momenta $p_T$. Discrepancies
arise toward high $p_T$, indicating the onset of radiative energy loss that we also address via a preliminary nonperturbative bremsstrahlung calculation.

[1] M. He, R. J. Fries and R. Rapp, Phys.Rev. C 86,014903 (2012).
[2] F. Riek and R. Rapp, Phys. Rev. C 82, 035201 (2010);
K. Huggins and R. Rapp, Nucl. Phys. A896, 24 (2012).
[3] M. He, R. J. Fries and R. Rapp, Phys. Lett. B 701, 445 (2011).
[4] M. He, R. J. Fries and R. Rapp, Phys. Rev. Lett. 110, 112301 (2013).
[5] M. He, R. J. Fries and R. Rapp, Phys. Lett. B 735, 445 (2014).
[6] M. He, R. J. Fries and R. Rapp, Phys. Rev. C 91, 024904 (2015).

Speaker: Min He (Nanjing University of Sci. & Tech.)

M.He_HardProbes, Sep.2016.pdf

82 Measurements of electrons from semi-leptonic heavy flavor decays in p+p and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at STAR

Heavy quarks are predominantly produced at early stages of high-energy heavy-ion collisions due to their large masses, and thus experience the whole evolution of the Quark-Gluon Plasma (QGP). Studies of interactions between heavy quarks and the QGP can provide new insights to the properties of the QGP. Heavy quark production measured in p+p collisions serves as a baseline to similar measurements in heavy-ion collisions, and is expected to be described by perturbative Quantum Chromodynamics calculations. Therefore measurements of heavy quark production via measuring the electrons from semi-leptonic decays of heavy flavor hadrons, also known as Non-Photonic Electron (NPE), in both p+p and Au+Au collisions are crucial.

In this talk, we will present the updated results of NPE production in p+p collisions at $\sqrt{s}$ = 200 GeV from the STAR experiment with much improved precision and wider kinematic coverage than previous measurements. We will also show the results of B-hadron contribution to NPE extracted from azimuthal correlations between NPE and charged hadrons in p+p collisions. The nuclear modification factor ($R_{AA}$) for NPE in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using 2010 data will be presented. Finally, we will show the analysis status of separating B- and D-decayed electrons utilizing the new Heavy Flavor Tracker as well as measuring NPE $R_{AA}$ in Au+Au collisions with 2014 data.

Speaker: Yaping Wang (Central China Normal University CCNU (CN))

2-4NPE_at_STAR_HP2016_Yaping_final.pdf

83 Heavy Quark Diffusion Dynamics in Quark-Gluon Plasma under Strong Magnetic Fields

We discuss heavy-quark dynamics in the quark-gluon plasma under a strong magnetic field induced by colliding nuclei. By the use of the diagrammatic resummation techniques for Hard Thermal Loop and the external magnetic field, we show analytic results of heavy-quark diffusion constant and drag force which become anisotropic due to the preferred spatial orientation in the magnetic field. We argue that the anisotropic diffusion constant gives rise to an enhancement/suppression of the heavy-quark elliptic flow depending on the transverse momentum.

K. Fukushima, K. Hattori, H.-U. Yee, and Y. Yin, ``Heavy Quark Diffusion in Strong Magnetic Fields at Weak Coupling and Implications for Elliptic Flow,'' Phys. Rev. D 93 (2016) 074028 [arXiv:1512.03689 [hep-ph]].

Speaker: Koichi Hattori (Fudan University; RIKEN-BNL Research Center)

HardProbes2016_Hattori.pptx

Parallel Session IV: High pT Correlations (II)

Convener: Zuo-tang Liang (SDU)

84 Photon-Jet Correlations in pp and PbPb collisions at 5.02 TeV with CMS

Electromagnetic probes such as photons do not participate in the strong interaction, and thus provide a clean measurement of the initial state in nuclear collisions. Correlations of photons balancing with jets in PbPb collisions constitute the golden channel to study parton energy loss in strongly interacting matter, since the photon not only determines the initial transverse momentum of the balancing parton, but also preferentially selects quark jets. We will present new results from pp, pPb, and PbPb collisions at 5.02 TeV collision energy, including the high statistics data collected with the CMS detector in the 2015 LHC run. The results include detailed studies of azimuthal and momentum correlations of isolated photons and associated jets, as well as jet I_AA, as a function of photon p_T and collision centrality.

Speaker: Christopher Mc Ginn (Massachusetts Inst. of Technology (US))

hp2016GammaJet_20160914_CFMFinal.pdf

85 Measurements of photon+jet production in 5 TeV pp and Pb+Pb collisions with the ATLAS detector

Measurements of prompt high-pT photon and associated jet production are a valuable way to explore how fast partons lose energy in the hot, deconfined medium created in relativistic heavy ion collisions. Since the photon pT is approximately balanced by the initial parton pT at leading order, these events can provide insight on how energy loss depends on the parton pT before quenching. Additionally, the leading jets in these events are likely to be quark-initiated. Thus, together with measurements of inclusive jet suppression, they may also provide a handle on the parton flavor dependence of energy loss. Photon+jet production measurements in the LHC Run 1 data showed that the jet-to-photon pT balance ratio, xJg = pTjet/pTphoton, and the per-photon jet yield, RJg, are systematically suppressed in more central collisions, while the photon+jet azimuthal correlation, Delta-phi, is unmodified. In the higher-luminosity, higher-collision-energy LHC Run 2 data, photon+jet events can be explored with greater statistical precision and in a more differential manner. In this analysis, events containing an isolated photon with pT > 60 GeV are studied in 520/ub and 26/pb of 5 TeV Pb+Pb and pp collision data. Measurements by ATLAS of xJg, RJg, and Delta-phi are presented in pp collisions and as a function of centrality in Pb+Pb collisions.

Speaker: Brian Cole (Columbia University (US))

HP2016ATLAS GammaJet_v4.pdf

HP2016ATLAS GammaJet_v5.pdf

86 Energy flow and transverse momentum balance in gamma-jets and dijet events of heavy-ion collisions

We develop a Linear Boltzmann Transport model for jet propagation in quark-gluon plasma in high-energy heavy-ion collisions. In this model, we take special consideration of recoiled partons from both elastic scattering and induced gluon radiation processes and their further propagation. Along with a recombination model for the hadronization processes, our simulations can provide a fairly realistic description of not only the medium modification of the reconstructed jets but also the jet-induced medium excitation in the underlying hydrodynamic background.

In this talk, we will discuss various jet observables in gamma-jets and dijet events and compare our results with the experimental data. Jet fragmentation function and jet shape are studied to look inside the jet structure. The radius R is extended in our jet shape study to look at the transverse momentum distribution outside the jet cone. We also investigate the transverse momentum balance as a function of opening angles around jets in dijet events. In particular, we calculate and compare the energy flow around the jet axis in gamma-jets and dijet events. Our results show the sensitivity of such spatial distribution of energy to the jet-medium interaction strength in the quark gluon plasma.

Speaker: Tan Luo (Central China Normal University)

2-3-HP2016-TanLuo.pdf

87 Near-side jet peak broadening in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV

Two-particle angular correlation measurements are sensitive probes of the interactions of the medium formed in heavy-ion collisions and the particles propagating through it. Such measurements are done by determining the distribution of the relative pseudorapidity ($\Delta\eta$) and azimuthal angle ($\Delta\varphi$) of particles with respect to a higher $p_{\rm T}$ trigger particle ($1 < p_{\rm T,trig} < 8~\text{GeV}/c$). The near-side peak is fitted, accounting for $\Delta\eta$-independent long-range correlations, and the centrality evolution of the width (variance) of the fitted distribution is investigated. In Pb-Pb collisions a significant broadening of the near-side peak in the $\Delta\eta$ direction is observed from peripheral to central collisions, while in the $\Delta\varphi$ direction the peak is almost independent of centrality. For the 10% most central events, a departure from the Gaussian shape is also observed at low transverse momentum ($1 < p_{\rm T,assoc} < 2~\text{GeV}/c$, $1 < p_{\rm T,trig} < 3~\text{GeV}/c$). In this contribution the results obtained by the ALICE experiment in Pb-Pb and pp collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV will be shown, and they will be interpreted in terms of radial and elliptic flow by comparing them to AMPT model simulations.

Speaker: Monika Kofarago (Nikhef National institute for subatomic physics (NL))

Kofarago_HardProbes2016.pdf

88 Studies of Jet Quenching with Jet-Track Correlations at CMS

The jet quenching phenomenon has been studied extensively to assess the properties of the Quark Gluon Plasma. Quenching manifestations appear in a variety of experimental observables, showing medium-induced changes to the jets observed in heavy ion collisions with respect to reference measurements in vacuum-like proton-proton collisions. Studying properties of reconstructed jets via two-dimensional angular correlations of all particles produced in the collisions with respect to jet(dijet) axis, allows simultaneously to assess the medium induced modifications to the jet shapes, fragmentation, extending these measurements to large angles, as well as to explore the angular patterns of energy flow due to quenching. Final results of the charged particle densities and energy flow about the jet direction as a function of relative azimuth and relative pseudorapidity from PbPb and pp collisions recorded by the CMS will be presented. Contributions to the event-wise jet-hadron correlations from medium-induced modifications of jets, and the effects of potential medium response to the jet propagation will be discussed.

Speaker: Dragos Velicanu (Massachusetts Inst. of Technology (US))

DragosVelicanu_JetTrackCorrelations_HardProbes2016_v1.pdf

Parallel Session IV: Quarkonia Production (I)

Convener: Feng Liu (Central China Normal University)

89 J/$\psi$ production in proton+proton and heavy-ion collisions at STAR

The discovery of the J/$\psi$ meson opened the door to studying the heavy quark-antiquark system. This not only provides valuable knowledge for our understanding of Quantum Chromodynamics (QCD), but also plays an important role as a standard candle for discovering new physics. Quark Gluon Plasma (QGP) is a new phase of matter which surprisingly behaves like a perfect fluid, and it can be created in high energy heavy-ion collisions. Comparing the production properties of quarkonium states in proton+proton and heavy-ion collisions plays a crucial role in exacting the QGP properties, for example the nuclear modification factor ($R_{AA}$) and elliptic flow ($v_2$) over a broad $p_T$ range.

The STAR experiment now has the capability of studying the quarkonium states via the dimuon channel with the newly installed Muon Telescope Detector. In this talk, the J/$\psi$ production cross-section, the dependence of J/$\psi$ production yield on charged-particle multiplicity in proton+proton collisions at \sqrt{s} = 200 and 500 GeV, and the measurements of $R_{AA}$ and $v_2$ of J/$\psi$ in Au+Au collisions at \sqrt{S_{NN}} = 200 GeV using dielectron and dimuon channels at the STAR experiment will be presented. The comparisons between the measurements and various model calculations will also be discussed.

Speaker: Yi Yang (National Cheng Kung University)

2_1YiYang_HP2016_20160924.pdf

90 Charmonium production in Pb--Pb collisions measured by ALICE at the LHC

The ALICE experiment is dedicated to the study of the Quark-Gluon Plasma (QGP), a state of matter where, due to high temperature and energy density, quarks and gluons are deconfined.

One of the probes studied to investigate this state of matter is the production of charmonium states, such as the J/$\psi$ and the $\psi$(2S). Indeed, the presence of the QGP is expected to modify the charmonium production yields, due to a balance between the color screening of the charm quark potential and a recombination mechanism.

A suppression of the production yields in heavy-ion collisions with respect to pp collisions scaled by the mean number of binary nucleon-nucleon collisions was observed by ALICE in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 2.76 TeV. The observed suppression is smaller than the one found by PHENIX at an order of magnitude lower collision energy. This behavior can be explained by a stronger contribution from recombination processes at LHC than at lower energies.

In this presentation, we will report on the new results for the charmonium production in Pb-Pb collisions measured at forward rapidity with the the muon spectrometer of ALICE at $\sqrt{s_{\rm NN}}$ = 5.02 TeV and their comparison with previous results and model predictions.

Speaker: Victor Jose Gaston Feuillard (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))

Victor_Feuillard_HP_Talk.pdf

91 Quarkonium production in proton-lead and lead-lead collisions at $\sqrt{s_{NN}}$=5 TeV with LHCb

see abstract

Speaker: Burkhard Schmidt (CERN)

Quarkonium Production in LHCb.pdf

92 Charmonium production and phenomena in pp, pPb and PbPb collisions at 2.76 and 5.02 TeV with CMS

A variety of effects modify the charmonium production in PbPb collisions with respect to pp collisions, including melting in the quark gluon plasma and statistical recombination, which can have a different impact on the J/Psi and the Psi(2S) mesons. Additional effects, like modification of nPDFs, initial-state energy loss and nuclear break-up, all probed also in pPb collisions, can affect the measured PbPb yield. Using pp and PbPb data at sqrt(s_NN) = 2.76 TeV, the CMS Collaboration has previously reported that the Psi(2S) meson is more suppressed than the J/Psi at midrapidity and high p_T (>6.5 GeV/c), but a hint of less suppression at forward rapidity and intermediate pt (1.6<|y|<2.4, p_T>3 GeV/c). New results on the relative J/Psi and Psi(2S) modification, based on the pp and PbPb data collected at sqrt(s_NN) = 5.02 TeV by CMS in 2015, will be reported. In addition, prompt J/Psi results in pPb collisions at 5.02 TeV and in PbPb collisions at 2.76 TeV, including v_2 and R_AA, will be presented over a wide kinematic and centrality range (3 < p_T <30 GeV/c, |y|<2.4, and fine event-centrality intervals).

Speaker: Emilien Chapon (Centre National de la Recherche Scientifique (FR))

chapon_HardProbes2016.pdf

93 Measurement of quarkonia production in 5 TeV proton-proton and heavy-ion collisions with the ATLAS detector

The in-medium suppression of heavy quarkonia production in heavy-ion collisions, with respect to proton-proton collisions, serves as a sensitive probe for studying the QGP. A full assessment of the suppression requires understanding effects present in the hot and dense medium in the A-A collisions as well as cold nuclear effects in the small-sized p+A collision. Based on proton-lead collision data collected in 2013 and proton-proton and lead-lead collision data collected in 2015 at the LHC, the ATLAS experiment can study J/psi, psi(2S) and Upsilon(nS) production via the di-muon decay channel. The charmonium states are separated into contributions from B-hadron decays and prompt production. The nuclear modification factors and excited-to-ground state ratios will be presented in intervals of transverse momentum, rapidity and centrality.

Speaker: Sebastian Tapia Araya (Federico Santa Maria Technical University (CL))

2_5HP2016_quarkonia_in_ATLAS_5TeV_v2.pdf

Parallel Session IV: Simulation of Hard Processes in A+A

Convener: Yacine Mehtar-Tani (INT, University of Washington)

94 Event-by-event simulations of jet modification using the MATTER event generator.

The modification of hard jets in the Quark Gluon Plasma (QGP) is studied using the MATTER event generator. Based on the higher twist formalism of energy loss, the MATTER event generator simulates the evolution of highly virtual partons through a medium. These partons sampled from an underlying PYTHIA kernel undergo splitting through a combination of vacuum and medium induced emission. The momentum exchange with the medium is simulated via the jet transport coefficient $\hat{q}$, which is assumed to scale with the entropy density at a given location in the medium. The entropy density is obtained from a relativistic viscous fluid dynamics simulation (VISH2+1D) in 2+1 space time dimensions. Results for jet and hadron observables are presented using both an independent fragmentation model and using the Texas A&M recombination simulation. This talk will focus on the physics input and simulation details of the MATTER event generator as compared to a variety of test observables.

Speaker: Michael Kordell (Wayne State University)

II-1-HP2016_talk1.pdf

95 First Results with HINJING++ on High-Energy Heavy-Ion Collisions

First calculated results with the new HIJING++ will be presented here for hadron production in high-energy heavy ion collisions. The recently developed HIJING++ version based on the latest version of PYTHIA8 and contains all the nuclear effects has been included in the HIJING2.1. We also included an improved version of the shadowing parametrization and jet quenching. Here we summarize the mayor changes of the new program code beside the comparison between experimental data.

Speaker: Gergely Gabor Barnafoldi (Wigner RCP Hungarian Academy of Sciences (HU))

BarnafoldiGG_HP16_2016_v6.pdf

96 Heavy Ion Collisions with General Purpose Event Generators

We present the first results from extending the Pythia model for Multiparton Interactions to collisions of heavy nuclei. The Pythia MPI model is a very well established description for pp minimum bias events, and using it to extrapolate to heavy ion collisions is therefore desirable.
In order to break HI collisions down to constituent proton collisions, we discuss extensions of the Glauber model, to also include diffractive excitation, which we find to bear some importance when calculating final states. We subsequently introduce a framework in which a pA collision is broken down into a single pp collision spanning the whole available rapidity range for the collision, and several spanning a smaller range, similar to the old Fritiof model for soft collisions, plus diffractive exitations. We find that this description reproduces centrality inclusive -and exclusive data rather well, and provides a good starting point for testing microscopic, QCD based models of collectivity. We finally discuss the prospects of including rope hadronization, corrections to the Lund string in busy environments, to account for collective effect

Speaker: Christian Bierlich (Lund University (SE))

bierlich.pdf

97 HYDJET++ model as a hot mixture of jets and hydrodynamics at ultra-relativistic heavy-ion collisions

HYDJET++ model combines the description of soft processes with the treatment of hard partons propagating hot and dense nuclear medium. The model is employed for the analysis of PbPb collisions at LHC energies. The cross-talk of elliptic $v_2$ and triangular $v_3$ flow in the model generates both even and odd harmonics of higher order, as well as long-range azimuthal dihadron correlations ("ridge" structure). The simple modification of the model via introducing the distribution over spatial anisotropy parameters permits HYDJET++ to reproduce both $v_2$ and $v_3$ flow fluctuations and related to it eccentricity fluctuations of the initial state. The data on momentum spectra and elliptic flow of charmed mesons are reproduced by HYDJET++ including thermal and non-thermal charm production mechanisms. A tolerable agreement of HYDJET++ predictions with the data for hard probes (including such observables as high-pT hadron and jet nuclear modification
factors, and specific modification of longitudinal and radial jet profiles) testifies in favour of successful treatment of the hard component based on PYQUEN event generator.

Speaker: Sergey Petrushanko (M.V. Lomonosov Moscow State University (RU))

Petrushanko_HP16.pdf

Round Table Discussion: Jet Quenching MC

Conveners: Abhijit Majumder (Wayne state university), Marta Verweij (CERN)

98 Status report: Hybrid strong/weak coupling model

Speaker: Daniel Pablos (Universitat de Barcelona)

mchybrid.pdf

99 Status report: LBT

Speaker: Tan Luo (Central China Normal University)

HP2016-MC-TanLuo.pdf

HP2016-MC-TanLuo.pptx

100 Status report: Martini

Speaker: Sangyong Jeon (McGill University)

talk_wuhan_jets_2016.pdf

101 Status report: QPYTHIA

Speaker: Liliana Apolinario (Instituto Superior Tecnico (PT))

QPYTHIA status report.pdf

102 Status report: MATTER

Speaker: Michael Kordell (Wayne State University)

HP2016_talk2.pdf

103 Discussion with panel

Sunday, 25 September

Parallel Session V: High pT Correlations (III)

Convener: Daicui Zhou (Central China Normal University CCNU (CN))

104 $\pi^0$-hadron correlations in pp and Pb-Pb collisions and $\pi^0$ elliptic flow in Pb-Pb collisions measured at the ALICE experiment

The study of the azimuthal correlation and anisotropy with $\pi^0$ offers a powerful way to investigate the properties of strongly interacting matter created in ultra-relativistic heavy-ion collisions. In this talk, we present the measurement of two-particle correlations of $\pi^0$ trigger particles with associated charged particles versus azimuthal angle difference ($\Delta\varphi$) in pp and central Pb–Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV, as well as the measurement of the elliptic flow ($v_2$) of π0 in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV at the ALICE experiment. $\pi^0$ are detected by the ALICE electromagnetic calorimeter EMCal for transverse momenta $8< p_T <16$ GeV/c, and charged particles are measured by the ALICE main tracking detectors ITS and TPC for $0.5 < p_T < 10$ GeV/c, both at mid-rapidity. For $\pi^0$-hadron correlations, the per-trigger yield modification factors ($I_{AA}$) are extracted on the near and away side and are compared with results from models and other experiments. For $\pi^0$ $v_2$, the current status will be presented. Both measurements serve as important investigation of the medium modified fragmentation pattern and the path-length dependence of energy loss in QGP, as well as the corresponding physics interpretation.

Speaker: Xinye Peng (Central China Normal University CCNU (CN))

xinye-hardprobe-v10.pdf

105 Probing Transverse Momentum Broadening via Dihadron and Hadron-jet Angular Correlations in Relativistic Heavy-ion Collisions

Dijet, dihadron, hadron-jet angular correlations have been reckoned as important probes of the transverse momentum broadening effects in relativistic nuclear collisions.
When a pair of high-energy jets created in hard collisions traverse the quark-gluon plasma produced in heavy-ion collisions, they become de-correlated due to the vacuum soft gluon radiation associated with the Sudakov logarithms and the medium-induced transverse momentum broadening.
For the first time, we employ the systematical resummation formalism and establish a baseline calculation to describe the dihadron and hadron-jet angular correlation data in $pp$ and peripheral $AA$ collisions where the medium effect is negligible.
We demonstrate that the medium effects, especially the so-called jet quenching parameter $\hat q$, can be extracted from the angular de-correlations observed in $AA$ collisions.
A global $\chi^2$ analysis of dihadron and hadron-jet angular correlation data renders the best fit $\langle \hat q L\rangle_{\textrm{tot}} \sim 14 \textrm{GeV}^2$ for a quark jet at RHIC top energy, with $L$ the typical traversed medium length.
Further experimental and theoretical efforts along the direction of this work shall significantly advance the quantitative understanding of transverse momentum broadening and help us acquire unprecedented knowledge of jet quenching parameter in relativistic heavy-ion collisions.

Speaker: Shu-yi Wei (CCNU)

qhat.hp2016.pdf

106 Dijet pseudorapidity and pT measurement in pp and pPb collisions at 5.02 TeV with CMS

The normalized dijet pseudorapidity distributions in pPb collisions can reveal the nuclear modifications of parton distribution functions (nPDF). Measurements as a function of average dijet transverse momentum could enable the test of the nPDF at different Q^2 scales. Moreover, recent theoretical studies based on NLO calculations show that the constraining power of pPb data on nPDF fits can be improved by the knowledge of the corresponding measurements in pp collisions. In this talk, the updated dijet pseudorapidity measurements in pPb collisions at 5 TeV in various of dijet transverse momentum ranges, as well as the corresponding reference distributions in pp collisions collected in 2015, will be presented. The measured distributions are compared to pQCD calculations with different sets of proton and nuclear PDFs.

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

20160925-HP2016_yenjie-v3.pdf

107 Characterizing the away-side jet with robust flow background subtraction via two-particle and three-particle correlations in Au+Au collisions at $\sqrt{s_{_\mathrm{NN}}}=200$ GeV in STAR

Jets are modified in relativistic heavy-ion collisions due to jet-medium interactions. Measurements of jet medium modifications have so far been obscure because of the large underlying anisotropic flow background. In this analysis we devise a novel method to subtract the flow background using data. We select events with a large recoil momentum ($P_x$) within a pseudorapidity ($\eta$) window of $0.5<|\eta|<1$ from a high-$p_T$ trigger particle to enhance the away-side jet population. Di-hadron azimuthal correlations are analyzed with associated particles in two $\eta$ ranges ($−0.5<\eta<0$ and $0<\eta<0.5$) symmetric about midrapidity, one (“close-region”) close to and the other (“far-region”) far away from the $P_x$ selection $\eta$ window. The away-side jet contributes to the close-region but not as much to the far-region due to the large $\eta$ gap, while the flow contributions are equal. Assuming the $\Delta\phi$ shape of jet-like correlations does not depend on $\Delta\eta$, the correlation difference measures the away-side jet shape where the anisotropic flow background is cleanly subtracted.

The away-side jet correlation width is studied in Au+Au collisions at $\sqrt{s_{_\mathrm{NN}}}=200$ GeV as a function of centrality and associated particle $p_T$. The width is found to increase with centrality at modest to high associated particle $p_T$. The increase can arise from jet-medium modifications, event averaging of away-side jets deflected by medium flow, and/or simply nuclear $k_T$ broadening. To further discriminate various physics mechanisms, a three-particle correlation analysis is conducted with robust flow background subtraction also using data. Based on this analysis we discuss possible physics mechanisms of away-side broadening of jet-like correlations.

Speaker: Kun Jiang (University of Science and Technology of China)

HP_0925_2016_Kun_v2.pdf

108 Heavy-flavor jets with CMS

The energy loss of jets in heavy-ion collisions is expected to depend on the mass and flavor of the initiating parton. Thus, measurements of jet quenching with identified partons place powerful constraints on the thermodynamic and transport properties of the hot and dense medium. We present recent result on heavy flavor jet spectra and nuclear modification factors of jets associated to charm and bottom quarks in both pPb and PbPb collisions. A new measurement of the dijet asymmetry of pairs of b-jets, based on the 5.02 TeV pp and PbPb data collected during the 2015 run, will be presented.

Speaker: Cheng-Chieh Peng (Purdue University (US))

Heavy_Flavor_Jet_CMS_ChengChieh.pdf

Parallel Session V: High pT hadron suppression in A+A (I)

Convener: Takao Sakaguchi (BNL)

109 Transverse momentum spectra and nuclear modification of charged particles at $\sqrt{s_\mathrm{NN}}=5.02$ TeV with ALICE at the LHC

Transverse momentum spectra of charged particles are important baseline measurements of perturbative QCD particle production in pp collisions and, in Pb-Pb collisions, they provide insight on the parton energy loss in the hot and dense QCD medium. In this contribution we present the ALICE measurements of transverse momentum spectra in pp and Pb-Pb collisions at the unprecedented energy of $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Measurements in Pb-Pb collisions are obtained as a function of the centrality of the collision and presented in terms of the nuclear modification factor $R_{\mathrm{AA}}$. The results are compared to previous measurements at lower collision energy and confronted with theoretical expectations from Monte Carlo event generators (pp) and model calculations of in-medium jet quenching (Pb-Pb).

Speaker: Michael Linus Knichel (Ruprecht-Karls-Universitaet Heidelberg (DE))

MKNICHEL_RAA_HardProbes2016_1.pdf

110 Charged particle nuclear modification factor in PbPb at 5.02 TeV with CMS

In the high-luminosity 5.02 TeV collision-energy per nucleon pair PbPb and pp data provided by LHC in 2015, CMS measured the nuclear modification factor of charged particles from a transverse momentum of 0.7 GeV/c to 400 GeV/c in the central rapidity region. The centrality dependence of the nuclear modification factor is explored in several bins of collision centrality, from the most central 0-5% to the peripheral 50-70% centrality range. Comparisons of the measured nuclear modification factor of charged particles at 5.02 TeV are made to theory calculations and to measurements at lower collision energies. The nuclear modification factors are also compared to the measurements at 2.76 TeV with charged particles and fully reconstructed jets.

Speaker: Austin Alan Baty (Massachusetts Inst. of Technology (US))

HP2016_Baty_v3.pdf

111 Quantifying jet transport properties via large $p_T$ hadron production

Nuclear modification factor $R_{AA}$ for large $p_T$ single hadron is studied
in a next-to-leading order (NLO) perturbative QCD (pQCD) parton model
with medium-modified fragmentation functions (mFFs) due to jet quenching
in high-energy heavy-ion collisions. The energy loss of the hard partons in the QGP is incorporated in the mFFs which utilize two most
important parameters to characterize the transport properties of the hard parton jets: the jet transport parameter $\hat q_{0}$ and the mean
free path $\lambda_{0}$, both at the initial time $\tau_0$.
A phenomenological study of the experimental data for $R_{AA}(p_{T})$ is performed to constrain the two parameters with simultaneous $\chi^2/{\rm d.o.f}$ fits to RHIC as well as LHC data.
We obtain for energetic quarks $\hat q_{0}\approx 1.1 \pm 0.2$ GeV$^2$/fm and $\lambda_{0}\approx 0.4 \pm 0.03$ fm in central $Au+Au$
collisions at $\sqrt{s_{NN}}=200$ GeV, while $\hat q_{0}\approx 1.7 \pm 0.3$ GeV$^2$/fm, and $\lambda_{0}\approx 0.5 \pm 0.05$ fm in central
$Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV.
Numerical analysis shows that the best fit favors a multiple scattering picture for the energetic jets propagating through the bulk medium,
with a moderate averaged number of gluon emissions. Based on the best constraints for $\lambda_{0}$ and $\tau_0$, the estimated value for the
mean-squared transverse momentum broadening is moderate which implies that the hard jets go through the medium with small reflection. [Zhi-Quan Liu, Hanzhong Zhang, Ben-Wei Zhang, Enke Wang，Eur. Phys. J. C (2016) 76:20]

Speaker: Hanzhong Zhang (IOPP, CCNU, CHINA)

1-3-HP2016 - zhz2.ppt

112 Neutral meson production in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

The ALICE experiment is mainly devoted to the study of Quark-Gluon Plasma (QGP) expected to be created in heavy-ion collisions at the LHC and RHIC $AA$ collision energies. In the early stage of such collisions, partons and photons can be produced in energetic hard processes. High energy partons will interact with the QGP, and from the measurement of the particles issued from the parton fragmentation in vacuum, one can infer transport properties of the QGP. Study of high-$p_{\rm T}$ hadrons production is important to constrain the properties of the hot dense medium. The strong suppression of high-$p_{\rm T}$ hadrons in heavy-ion collisions has been explained by the energy loss of the partons in medium and it can be investigated experimentally via the nuclear modification factor (${R_{AA}}$) of hadrons.

ALICE measures neutral mesons at mid-rapidity in a wide $p_{\rm T}$ range in $pp$, $p$-Pb and Pb-Pb collisions. Neutral mesons (${\pi^{0}}$ and $\eta$) are reconstructed via complementary methods, using the ALICE electromagnetic calorimeters, PHOS and EMCal, and by the central tracking system, identifying photons converted to $e^{+}e^{-}$ pairs in the material of the inner barrel detectors (TPC and ITS). Measurement of neutral meson spectra in $pp$ collisions at $\sqrt{s}$ = 0.9, 2.76, 7 and 8 TeV provide valuable comparison data for pQCD calculations and allow to study scaling properties of hadron production at the LHC energies. The study of neutral meson production in $p$-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV is of importance to quantify the suppression and disentangle initial and final state effects on the suppression itself. The latest results of neutral meson production in $pp$, $p$-Pb and Pb-Pb collisions in LHC-Run1 will be shown in this presentation. The current status of neutral meson measurement in LHC-Run2 will be presented.

Speaker: Tsubasa Okubo (Hiroshima University (JP))

HP2016_TsubasaOkubo_v6.pdf

113 Productions of $\eta$, $\rho^0$ and $\phi$ at large transverse momentum in Heavy ion Collisions with NLO pQCD

The transverse momentum spectrum of $\eta$ meson in relativistic heavy-ion collisions is studied at the next-to-leading-order (NLO) within the perturbative QCD, where the jet quenching effect in the QGP is incorporated with the effectively medium-modified $\eta$ fragmentation functions using the higher-twist approach. We show that the theoretical simulations could give nice descriptions of PHENIX data on $\eta$ meson in both $\rm p+p$ and central $\rm Au+Au$ collisions at the RHIC, and also provide numerical predictions of $\eta$ spectra in central $\rm Pb+Pb$ collisions with $\sqrt{s_{NN}}=2.76$~TeV at the LHC. The ratios of $\eta/\pi^0$ in $\rm p+p$ and in central $\rm Au+Au$ collisions at $200$~GeV are found to overlap in a wide $p_T$ region, which matches well the measured ratio $\eta / \pi^0$ by PHENIX. We demonstrate that, at the asymptotic region when $p_{T} \rightarrow \infty$ the ratios of $\eta/\pi^{0}$ in both $\rm Au+Au$ and $\rm p+p$ are almost determined only by quark jets fragmentation and thus approach to the one in $e^{+} e^{-}$ scattering; in addition, the almost identical gluon (quark) contribution fractions to $\eta$ and to $\pi$ result in a rather moderate variation of $\eta/\pi^{0}$ distribution at intermediate and high $p_T$ region in $\rm A+A$ relative to that in $\rm p+p$; while a slightly higher $\eta/\pi^{0}$ at small $p_T$ in $\rm Au+Au$ can be observed due to larger suppression of gluon contribution fraction to $\pi^{0}$ as compared to the one to $\eta$. The theoretical prediction for $\eta / \pi^0$ at the LHC has also been presented.

Also, we present our further studies on vector mesons such as $\rho^0$ and $\phi$ within the same framework. The theoretical predictions based on pQCD are thus firstly given which math well with the experimental measurements. It paved the way to the uniformly understanding of the strong suppression of single hadron productions at large transverse momentum which is a convincing evidence of the jet quenching effect.

Speaker: Wei Dai (Tsinghua University)

Dai_wuhan.pdf

Parallel Session V: Jet Modification in A+A (III)

Convener: Yaxian Mao (Central China Normal University CCNU (CN))

114 Coherence and resolution in jet formation inside a dense medium

Previous studies of the simplified escenario of a color antenna traversing a dense medium have led to the idea that a system of partons with a sufficiently small transverse size maintain coherence despite the multiple interactions with the dense medium, therefore radiating as a single source. Such a setup ignores important effects coming from the formation of the system which inevitably affect the coherence at later times. We study the more realistic case where gluons (both vacuum-like and medium-induced) are emitted inside a medium and show under which circumstances the two-parton system maintains coherence while going across the dense medium by considering interference effects in a second emission.

Speaker: Fabio Dominguez (Universidade de Santiago de Compostela)

DominguezHP2016.pdf

115 Transport coefficients from energy loss studies in an expanding QGP

Based on:

"Relating $\hat{q}$, $\eta/s$ and $\Delta E$ in an expanding Quark-Gluon Plasma"
A. Ayala, I. Dominguez, J. Jalilian-Marian and M. E. Tejeda-Yeomans
e-Print: arXiv:1603.09296 [hep-ph]
submitted to Phys. Rev. C

Speaker: Alejandro Ayala (UNAM)

1-2-HP2016-ayala.pdf

116 Time Dependent qhat from AdS/CFT

We present the first ever AdS/CFT calculation of $\hat{q}$ for a light quark jet as a function of position or, equivalently, time. Our result does not suffer from the gamma factor blow up of the usual time-independent AdS/CFT heavy quark setup and is qualitatively similar to, but about a factor of 2/3 larger than, the light flavor result from Liu, Rajagopal, and Wiedemann. Our findings can be immediately implemented into any $\hat{q}$-based energy loss model.

Our $\hat{q}$ derivation relies on our calculation of the average distance squared, $s^2(t)$, travelled by the endpoint of a string falling in an AdS$_3$-Schwarzschild spacetime. The early time behavior is ballistic, $s^2(t)\sim t^2$, but the late time behavior is the usual diffusive Brownian motion, $s^2(t)\sim t$. These late time dynamics are universal and depend only on the near-horizon physics, which allows us to generalize our results to arbitrary dimensions and thus make contact with the physics explored by RHIC and LHC.

Additionally, we find that AdS/CFT predicts angular ordering for radiation in medium, just as in vacuum, and in contradistinction to weak-coupling, with its anti-angular ordering prediction. Finally, our results also imply, sensibly, that AdS/CFT predicts a smooth interpolation between the angular correlations of open heavy flavor and light flavor observables.

Speaker: William Horowitz (University of Cape Town)

1-3-160925(HP2016)Horowitz.pptx

117 Jet studies in heavy ion collisions with the ATLAS detector

In relativistic heavy ion collisions, a hot medium with a high density of unscreened color charges is produced. Jets are produced at the early stages of this collision and are known to become attenuated as they propagate through the hot matter. One manifestation of this energy loss is a lower yield of jets emerging from the medium than expected in the absence of medium effects. ATLAS has provided a quantification of this jet suppression by the jet Raa measurement in run 1 of LHC. A factor of two suppression was seen in central heavy ion collisions with respect to pp collisions. The Raa exhibited only a week, if any, rapidity dependence, and a slow rise with increasing jet momentum. This talk summarizes the run 1 results on the inclusive jet production and the new results on dijet measurements.

Speaker: Radim Slovak (Charles University (CZ))

1-4-HardProbes16_Slovak.pdf

118 Azimuthal anisotropy of very high-p_T particles in PbPb collisions at 5.02 TeV with CMS

The elliptic and triangular azimuthal anisotropies of charged particles produced in PbPb collisions at sqrt(s_NN) = 5.02 TeV are measured with the CMS detector at the LHC over an extended transverse momentum (p_T) range up to approximately 100 GeV/c. The data cover both the low-p_T (~ 1 GeV/c) region associated with hydrodynamic flow phenomena and the high-pT region where anisotropic azimuthal distributions may reflect the path-length dependence of parton energy loss in the created medium. Several methods were used to extract the anisotropy Fourier coefficients, such as the scalar product and multi-particle cumulant methods. The data are compared to theoretical calculations involving parton energy loss in a dense QCD medium.

Speaker: Quan Wang (The University of Kansas (US))

HP2016.pdf

Parallel Session V: Quarkonia Production (II)

Convener: Ramona Vogt (University of California at Davis)

119 $\Upsilon$ production in p--Pb and Pb--Pb collisions with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) is devoted to the study of heavy-ion collisions at LHC energies. It is predicted that a deconfined state of nuclear matter, the Quark-Gluon Plasma (QGP), is created in such collisions. The production of heavy quarkonia is modified in the presence of a QGP compared to the production in pp and p--Pb collisions. In particular, a suppression by colour screening has been observed at SPS, RHIC and LHC energies. In addition, the measurements of charmonium production performed in Pb--Pb collisions at the LHC point to the presence of regeneration phenomena occurring in the QGP or at the phase boundary. Such effects are expected to be much smaller for bottomonia than for charmonia, which makes the former an ideal probe to study the suppression mechanism in heavy-ion collisions at LHC energies. In order to better address the hot and dense medium effects on bottomonium production, the contribution of cold nuclear matter effects is estimated studying proton-nucleus collisions.

In ALICE, $\Upsilon$ production is measured in the dimuon decay channel, down to zero transverse momentum and in the rapidity range 2.5 < $y$ < 4.
The recent ALICE results on $\Upsilon$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ =5.02 TeV will be presented and compared with previous measurements at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. A comparison with theoretical calculations will be performed as well. Results obtained in p-Pb collisions at $\sqrt{S_{\rm NN}}$ = 5.02 TeV will also be discussed.

Speaker: Gabriele Gaetano Fronze' (Universita e INFN Torino (IT))

HPTalk2RehearsalCC.pdf

120 Upsilon production in Au+Au collisions at √(s_NN )= 200 GeV with the STAR experiment

Quark-Gluon Plasma (QGP), a new state of matter where quarks and gluons are de-confined, is believed to have existed up to a few milliseconds after the Big Bang. Quarkonia could dissociate in the QGP due to color screening of quark-antiquark potential by the surrounding partons in the medium, which was suggested as a signature of QGP formation in heavy-ion collisions. Moreover, different quarkonium states may dissociate at different temperatures depending on their binding energies. This so-called sequential melting phenomenon could be used to deduce the temperature of the QGP. However, other effects, such as regeneration from uncorrelated heavy quark-antiquark pairs, shadowing and antishadowing of nuclear structure functions, co-mover absorption, need to be taken into account when interpreting experimental results. Compared to charmonia, bottomonia is much less affected by regeneration contribution and co-mover absorption at RHIC energies, making them a cleaner probe to the QGP.

Measurements of Upsilon production have been traditionally studied via the di-electron channel at STAR. Since 2014, a new detector, the Muon Telescope Detector (MTD), has been fully installed and taking data, allowing measurements of Upsilon production via the di-muon channel. Compared to the di-electron channel, the di-muon channel has better sensitivity to different Upsilon states due to the reduced bremsstrahlung radiation. In this talk, we will present new results on Upsilon suppression in both the di-electron and di-muon decay channels in Au+Au collisions at √(s_NN )= 200 GeV based on the full data sample taken in 2014. The measured results will be compared to those at the LHC and to theoretical calculations.

Speaker: Zaochen Ye (UNIVERSITY OF ILLINOIS AT CHICAGO)

Upsilon_ZaochenYe_HP2016_final.pdf

121 Bottomonium suppression in nucleus-nucleus and proton-nucleus collisions

We present the first application of the Comover Interaction Model (CIM) to $\Upsilon(nS)$ production in nucleus-nucleus and proton-nucleus collisions from fixed-target to collider energies. The CIM offers an elegant way to explain the relative suppression of the excited $\Upsilon$ states observed in proton-nucleus collisions at the LHC. From these relative suppressions, we are able to constrain the comover cross sections for the different bottomonium states which encapsulate final-state interactions. Together with initial-state effects, such as the nuclear modification of the parton densities, we obtain significant $\Upsilon(nS)$ suppressions in nucleus-nucleus collisions compared to the expected impact of the colour screening. This renders the interpretation of the sequential-suppression pattern observed by CMS in PbPb collisions more complex to interpret.

Speaker: Jean-Philippe Lansberg (IPN Orsay, Paris Sud U. / IN2P3-CNRS)

Lansberg-HP2016-240916.pdf

122 Dynamical bottomonium-suppression in a realistic AA background

The suppression of upsilon Y(1S) states in AA collisions, observed by the STAR collaboration at RHIC and by the CMS and ALICE collaboration at LHC, is one of the most convincing evidence for the creation of the quark gluon plasma. The precise survival of excited Y(2S) and Y(3S) states vs ground state could even allow to measure the highest temperature reached in those collisions, according for instance to the sequential suppression scenario which is substantiated by calculations of the dissociation temperature based on lattice potentials evaluated at finite temperature.

In our contribution, we address the question of upsilon dissociation resorting to a dynamical approach, i.e. the non-linear Schroedinger-Langevin equation (SLE). In this scheme, the time-dependent real potential implements the Debye-screening while the stochastic forces express the (hard) interactions between the QGP and the $b\bar b$ state, possibly leading to instantaneous dissociation. The SLE preserves unitarity and enables to treat the transitions between bound and open quantum states, which play an important role for excited state final populations. It allows to consider a realistic compact initial state, made of a linear superposition of upsilon eigenstates and to preserve quantum coherence in the time-evolution of the $b\bar b$ pair.
In a stationary QGP, our SLE naturally leads to asymptotic distributions of {Y(1S), Y(2S),...} following correct statistical weights, which allows to make the link with models based on the hypothesis of statistical recombination. This sanity check is a unique feature of our approach.

We will describe the most important properties of the SLE. On the theory side, contact will be made with the spectral function evaluated on the lattice. On the phenomenological side, we will then present the suppression prediction resulting from SLE embedded in state-of-the-art EPOS evolution scenario of the QGP background, both for RHIC and LHC energies. The pT and rapidity dependences of the yields will be discussed, as well as the absolute yields and the relative yield Y(nS)/Y(1S) as a function of the centrality.

Ref.:

• Annals of Physics 368 (2016) 267-295

• arXiv:1601.01443, accepted for publication in Nuclear Physics A

Speaker: Pol Gossiaux (Subatech)

Gossiaux Hard Probes 2016.pdf

123 Bottomonium production and phenomena in pp, pPb and PbPb collisions at 2.76 and 5.02 TeV with CMS

Bottomonia are important probes of the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. The production cross sections of the three Y states (1S, 2S, 3S) were measured by CMS in pp and PbPb collisions at 2.76 TeV. A strong suppression is observed in PbPb collisions, by up to a factor of 2 and 10 for the Y(1S) and Y(2S) respectively. The Y(3S) was not observed in PbPb collisions. This suppression was seen to depend on centrality, but not significantly on transverse momentum or rapidity. A surprising dependence of the excited over the ground state ratio on the global event activity was also found in pPb data, as well as in pp data. In all three systems, the yields for the three states are also observed to increase with increasing event activity. In this talk, we will present the final CMS results on bottomonium production in the three collisions systems, together with new results from pp collisions at 5.02 and 7 TeV, and from the high statistics 5.02 TeV PbPb data collected in 2015.

Speaker: Yongsun Kim (Korea University (KR))

CMS_bottomonia_HP2016_Yongsun2016_09_23_v9.pdf

10:10 Break

Parallel Session VI: Heavy Qaurk and Quarkonia Production

Convener: Dieter Roehrich (University of Bergen (NO))

124 Production of Muons from Heavy-Flavour Hadron Decays in Pb--Pb Collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE at the LHC

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 Quark-Gluon Plasma (QGP) is formed. Heavy quarks (charm and beauty) are among the important probes for the investigation of the properties of the QGP as they are created on a very short time scale in initial hard scattering processes and experience the whole evolution of the system, while losing energy in the interaction with the medium constituents.

The nuclear modification factor $R_{\rm AA}$, defined as the ratio of the particle yield measured in Pb-Pb collisions to the cross section in pp collisions scaled with the average nuclear overlap function, and/or the central-to-peripheral nuclear modification factor $R_{\rm CP}$, are relevant observables to quantify the energy loss effects.

New ALICE results concerning the production of muons from heavy-flavour hadron decays at forward rapidity in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV will be presented. The measurement of the production cross section and nuclear modification factors will be discussed. The progress on the studies as a function of transverse momentum and centrality will be shown. Data will be compared with previous measurements in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV.

Speaker: Zuman Zhang (Central China Normal University CCNU (CN))

RAA_muons_5TeV_HP_2016.9.25.pdf

125 Non-prompt J/Psi v_2 and R_AA in PbPb collisions at 2.76TeV with CMS

Beauty production and phenomena in heavy-ion collisions are considered one of the key measurements to address the flavour-dependence of in-medium energy loss in PbPb collisions at the LHC. The CMS experiment has excellent capabilities for measuring b-quark production thanks to the excellent performances of its muon and tracker system. In this talk, CMS will present the first measurement of the v_2 Fourier harmonic and the R_AA down to 3 GeV/c, for non-prompt J/Psi produced in B meson decays, in PbPb collisions at 2.76 TeV, as a function of transverse momentum, rapidity and event centrality.

Speaker: Mihee Jo (Centre National de la Recherche Scientifique (FR))

MiheeJo_HP2016_v6.pdf

126 Heavy quarkonium spectrum and diffractive production in a light-front Hamiltonian approach

We study exclusive heavy flavor vector meson production in diffractive deep inelastic scattering and ultra-peripheral heavy-ion collisions within the dipole picture. We obtain the mass spectrum and light-front wavefunctions of heavy quarkonium from the basis light-front quantization approach, using the one-gluon exchange interaction plus a confining potential inspired by light-front holography. We apply these light-front wavefunctions to exclusive charmonium and bottomonium production. The resulting cross sections are in reasonable agreement with electron-proton collision data at HERA and ultra-peripheral nucleus collision measurements at RHIC and LHC. The heavy quarkonium cross-section has model dependence on dipole model. We observe that the cross-section ratio of excited states to the ground state has a weaker dependence than cross-section itself. We suggest that measurements of excited states of heavy quarkonium production in future electron-ion collision experiments will impose rigourous constraints on heavy quarkonium light-front wavefunctions, thus improving our understanding of meson structure, which eventually will help us develop a precise description of the gluon distribution function at small-$x$ regime. This work was supported in part by the Department of Energy under Grant Nos. DE-FG02-87ER40371 and DESC0008485 (SciDAC- 3/NUCLEI).

Speaker: Guangyao Chen (Iowa State University)

2_3_XDVMP_HP.pdf

127 Excess of $J/\psi$ yield at very low $p_{T}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV measured with STAR experiment

Suppression of $J/\psi$ production in heavy-ion collisions due to color screening of quark and antiquark potential in the deconfined medium has been proposed as a signature of the QGP formation. Other mechanisms, such as the cold nuclear matter effects and charm quark recombination, can contribute to the observed modification of $J/\psi$ production in heavy-ion collisions. Recently, a significant excess of $J/\psi$ yield at very low $p_{T}$ ($<$ 0.3 GeV/c) was observed by the ALICE collaboration in peripheral Pb+Pb collisions at $\sqrt{s_{NN}}$= 2.76 TeV at forward-rapidity, which can not be explained by the above-mentioned effects. It has been hypothesized that such $J/\psi$'s are produced from the coherent photoproduction in Pb+Pb collisions at impact parameters smaller than twice the nuclear radius, which would be very challenging for the existing models developed to describe coherent photoproduction in ultra-peripheral collisions. Measurements of $J/\psi$ production at very low $p_{T}$ in different collision energies, collision systems, and centralities can shed new light on the origin of the excess.\

In this presentation we report the STAR measurements of $J/\psi$ production at very low $p_{T}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV at mid-rapidity. Centrality dependence of $J/\psi$ production cross section and nuclear modification factors at very low $p_{T}$ will be presented. Physics perspectives with Zr+Zr and Ru+Ru collisions scheduled for RHIC 2018 run will be discussed.

Speaker: Wangmei Zha (USTC/BNL)

HP2016_wangmei.pdf

128 Relative Yields and Nuclear Modification of Psi' to J/Psi mesons in p+p, p(3He)+A Collisions at sqrt(s_NN) = 200 GeV, measured in PHENIX

The PHENIX collaboration has measured the ratio of the Psi(2s) to the
Psi(1s) cross section in p+p and p(3He)+A collisions at forward and
backward rapidity. We find that in p+p collisions, the data are
consistent with expectations from a modified color evaporation model
of quarkonia formation. In p(3He)+A collisions, in the p(3He)-going
direction, within uncertainties there is an equivalent nuclear
modification of both Psi states. However, in the A-going direction,
the nuclear modification factor of the weaker bound Psi(2s) is a
factor of 2 less than that of the Psi(1s). Since these states are not
fully formed until after they exit the nucleus, interactions between
the fully formed charmonia and co-moving hadrons may be responsible
for this effect, consistent with the higher particle density in the
A-going direction relative to the p(3He)-going direction. This
mechanism may compete with color screening in a deconfined plasma in
A+A collisions to produce sequential suppression of excited quarkonia
states.

Speaker: Axel Drees (Stony Brook University)

2_5_Drees_PHENIX_HP2016.pdf

Parallel Session VI: High pT hadron suppression in A+A (II)

Convener: William Horowitz (University of Cape Town)

129 Strangeness production and nuclear modification at LHC energies

The presence of a strongly interacting medium produced in relativistic
heavy-ion (AA) collisions modifies the final transverse momentum (p$_{\mathrm{T}}$) spectra of hadrons with respect to proton-proton (pp) collisions. While the production at high-p$_{\mathrm{T}}$ is suppressed by in-medium energy loss of high-p$_{\mathrm{T}}$ partons, at lower p$_{\mathrm{T}}$ other mechanisms dominate strangeness production. In order to explore this issue, a system size scan of the production rates of strange
hadrons is warranted.

The ALICE Collaboration reports on the nuclear modification factors R$_{\mathrm{AA}}$
and R$_{\mathrm{pA}}$ of several light-flavour hadrons, including (multi)strange particles.
In addition, we also explore the crucial issue of how strangeness production scales with system size by presenting recent results on the multiplicity dependence of light-flavour production in pp collisions. The results are compared to measurements from lower energies and to predictions from QCD-inspired event generators.

Speaker: Oliver Busch (University of Tsukuba (JP))

talkHP2016OB.pdf

130 Measurement of azimuthal flow of soft and high-pT charged particles in 5.02 TeV Pb+Pb collisions with the ATLAS detector

The new experimental data collected by the ATLAS experiment during the 2015 heavy ion LHC run offers new opportunities to study properties of Quark-Gluon Plasma at unprecedented high temperatures and densities. Study of the azimuthal anisotropy of produced particles not only constrains our understanding of initial conditions of nuclear collisions and soft particle collective dynamics but also sheds light on jet quenching phenomena via measurement of flow harmonics at high transverse momenta. A new ATLAS measurement of elliptic flow and higher order Fourier harmonics of charged particles in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV in a wide range of transverse momenta, pseudorapidity (|η| < 2.5) and collision centrality will be presented. These measurements will be based on the Scalar Product, Event Plane and Two-Particle Correlation methods. Obtained results will be compared with experimental results at lower collision energies and discussed in the context of theoretical models.

Speaker: Klaudia Burka (Polish Academy of Sciences (PL))

HPslides_kburka.pdf

131 Beyond the Poisson Approximation: n Gluon Radiation in QGP

We present a novel technique for the calculation of the probability for emission of an arbitrary number of gluons radiated from a high-pT probe of the QGP. Our work is an extension of the maximal helicity violating (MHV) method in which the usual soft-collinear factor is classified according to its symmetry under gluon permutations.

For the purposes of illustration, we show the explicit form of the result for from 1 to 4 gluon emissions and present the general expression for any generic $n$ numbers of gluons. In particular, we compute for the first time the QCD corrections to the multi-gluon Poisson approximation. Since all current energy loss calculations assume that the Poisson distribution of photons from QED bremsstrahlung is a good approximation for the multi-gluon radiation in QCD, our results will prove invaluable to leading particle and jet energy loss modellers.

Speaker: Andriniaina Rasoanaivo (University of Cape Town)

Rasoanaivo.pdf

132 Medium modification of jet charge in heavy-ion collisions

The momentum-weighted sum of the charges inside a jet provides an experimental handle on the electric charge of fundamental strongly-interacting particles. Knowing the charge of the parton initiating a light-quark jet could be extremely useful both for testing aspects of the Standard Model and for characterizing potential beyond-the-Standard-Model signals not only in pp collisions, but also the medium effects in heavy-ion collisions. There is evidence for a p_T dependence of the jet charge distribution for a given jet flavor.
Within the jet product in pp collisions by pythia6, and parton energy loss in the frame work of PYQUEN model, we give our first prediction for the average value of the jet charge distribution for the leading jet in heavy-ion collision both at RHIC and LHC. It is shown that the jet charge is significant modified by the medium created during these reactions and an enhancement of jet change in A+A relative to p+p is observed due to jet quenching effect. Since obvious difference of jet charge can be found between quark and gluon jets, this could be useful to discriminate the energy loss pattern between quark and gluon. The averaged jet charge distribution may present distinct patterns when different models of the flavor dependence of parton energy are incorporated.

Speaker: Shi-Yong Chen (CCNU)

HP2016-Chen-Shiyong.pdf

133 The x and scale dependence of the transport coefficient $\hat{q}$

We take a closer look at the single particle nuclear modification factor ($R_{AA}$) and azimuthal anisotropy ($v_{2}$) of leading hadrons at high transverse momentum ($p_{T}$) at both RHIC and LHC collision energies. We focus on the established reduction in the interaction measure $\hat{q}/T^{3}$ between RHIC and LHC, as discovered by the JET collaboration. The centrality dependence of the $R_{AA}$ and $v_{2}$ at both these collision energies strongly suggests that the reduction is not caused by a temperature dependence in the ratio of $\hat{q}/T^{3}$ but rather by an energy dependence of $\hat{q}$.
We study this dependence by introducing an $x$ dependence in the distribution function that is integrated to obtain $\hat{q}$. We conjecture on possible forms of a scale dependence by relating $\hat{q}$ to an object similar to a transverse momentum dependent parton distribution function (TMDPDF). The ensuing operator product is then related to quantities that may be estimated in lattice QCD.

Speaker: Abhijit Majumder (Wayne state university)

5majumder_HP2016_parallel.pdf

Parallel Session VI: Initial Conditions

Convener: Tuomas Lappi (University of Jyvaskyla)

134 A Novel Approach For Event-By-Event Initial Conditions From Color Glass Condensate

The Color Glass Condensate (CGC) formalism with event-by-event fluctuations in the transverse plane has led to excellent results when coupled to viscous relativistic hydrodynamics. Recently, some of us have suggested analytic and semi-analytic solutions to event-averaged quantities in the CGC formalism based on a near field approximation [Phys. Rev. C 92, 064912 (2015)]. This approach gives a rather intuitive and simple picture of the classical gluon fields at the earliest times (tau < 1/Qs). In this talk we start out by reviewing this recent work. We also discuss results from subsequent evolution through viscous fluid dynamics. We then go on to describe how our work can be used to simulate ensembles of gluon field strength tensors and their energy momentum tensors event-by-event. Only static 2-D Yang Mills equations have to be solved numerically as the time evolution (up to 1/Qs) is already taken care of by the near field expansion. This promises gains in efficiency.

Speaker: Rainer Fries (Texas A&M University)

HP_2016.pdf

HP_2016.pptx

135 Proton structure fluctuations: constraints from incoherent diffraction and applications to pA collisions

Exclusive vector meson production can be used to directly probe the gluon density of a hadron. Measuring the cross section differentially in momentum transfer t makes it possible to determine the transverse density profile (via coherent diffraction) and density fluctuations (incoherent diffraction) of the target hadron. This knowledge on the geometric fluctuations of the proton is particularly important for understanding collective phenomena observed in proton-nucleus collisions.

We calculate coherent and incoherent diffractive vector meson production in photon-proton scattering. The dipole model used in the calculation is constrained by the proton structure function data. We demonstrate that incoherent gamma-p scattering is sensitive to sub-nucleon scale fluctuations. We also show that the effect of geometric fluctuations can be disentangled from saturation scale fluctuations.

The fluctuating proton, constrained by the HERA data, is then used as an input to calculations of proton-nucleus collisions. In particular, we use relativistic hydrodynamics to calculate azimuthal anisotropy coefficients and show that they are sensitive to initial state geometric fluctuations.

References:
H. Mäntysaari, B. Schenke, arXiv:1603.04349, to be published in PRL
H. Mäntysaari, B. Schenke, arXiv:1607.01711

Speaker: Heikki Mäntysaari (Brookhaven National Laboratory)

hp16_mantysaari.pdf

136 Pre-equilibrium Longitudinal Flow in the IPGlasma Framework for Pb+Pb Collisions at the LHC

In this talk, we debut a new formulation of IPGlasma and present the first systematic study of the effects of pre-equilibrium longitudinal flow on hadronic and electromagnetic observables in Pb+Pb collisions at 2.76 TeV and 5.02 TeV. The saturation physics based IPGlasma model naturally provides a non-zero initial longitudinal flow through its pre-equilibrium Yang-Mills evolution. Hydrodynamic simulations in (3+1)-dimensions allow us to study the effects of such flow, which deviates from local Bjorken flow and is usually not included in phenomenological studies. Because thermal photons are produced early during heavy-ion collisions, their spectra and flow anisotropy are more sensitive to the early non-zero longitudinal flow. The impact of pre-equilibrium longitudinal flow on direct photon observables is first explored in Pb+Pb collisions at both 2.76 TeV and 5.02 TeV. Effects on the event-by-event distribution of charged hadron vn, event-plane flow correlations and identified particle observables are quantified, and predictions at 5.02 TeV are highlighted. Finally, the sensitivity of the pre-equilibrium longitudinal flow to the IPGlasma/hydro switching time is discussed.

Speaker: Scott McDonald (McGill University)

McDonald_HP2016.pdf

137 Compact initial state for peripheral heavy ion reactions and its consequences

An initial state is created based field dominance and on flux-tubes or streaks in the transverse plane with local momentum and angular momentum conservation and local shear. The global dynamical consequences as well as polarization and correlations of produced particles will be discussed.

Speaker: Laszlo Pal Csernai

1-Csernai-Wuhan.pptx

138 Measurement of long-range azimuthal anisotropies and of forward-backward multiplicity correlations and longitudinal flow with the ATLAS detector

ATLAS measurements of correlations between particle pairs in relative azimuthal angle ($\Delta\phi$) and pseudorapidity separation ($\Delta\eta$), in $pp$ collisions at $\sqrt{s}$=2.76, 5.02 and 13~TeV, and in $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=5.02~TeV are presented. Prior measurements have shown that in $pp$ collisions with a large multiplicity of produced particles, a long-range structure,commonly called the ``ridge'', develops along $\Delta\eta$ at $\Delta\phi\sim$0. However, due to the presence of the large away-side jet, the full $\Delta\phi$ dependence of the long-range correlation could not be studied previously. In this analysis, a template fitting procedure is implemented to determine the contributions from dijets to the correlations, using low-multiplicity events, and extract the genuine long-range correlation. The long-range correlations are shown to be present even in events with a small multiplicity of produced particles, implying that the long-range correlations are not unique to rare high multiplicity events. The properties of the correlation are shown to be remarkably similar to that observed in $p$+Pb collisions. Study of these long range correlations using multi-particle cumulants are also presented. New results on how the long-range correlations are affected by the presence or absence of hard processes in the $pp$ collision are presented.

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

sasha_2pc_2016_09_24.pptx

Parallel Session VI: Jet Modification in A+A (IV)

Convener: Toru Sugitate (Hiroshima University (JP))

139 Jet Substructure through Splitting Functions in pp and PbPb collisions with CMS

A measurement of the hardest splitting of a parton with high transverse momentum in proton-proton and PbPb collisions at a center-of-mass energy of 5.02 TeV with the CMS detector is presented. For this analysis, a jet grooming technique is used to isolate the large scale structure of the jet. The measurement of this hard splitting probes the virtuality evolution of a parton in the medium, as well as the role of (de)coherent gluon emitters. The splitting functions in PbPb collisions are measured as function of the transverse momentum of the jet and collision centrality and are compared with the reference spectra from pp collisions.

Speaker: Marta Verweij (CERN)

160925_HPSplitFuncMVerweij.pdf

140 Measurement of the Shared Momentum Fraction $z_g$ using Jet Reconstruction in p+p and Au+Au Collisions with STAR

Light quark and gluon jet quenching in heavy ion collisions is described within the overwhelming majority of models as resulting predominantly from pQCD-type gluon radiation,
but details of the underlying mechanisms differ greatly.
One key difference lies in the treatment of the Altarelli-Parisi, AP, splitting functions.
While in some models, such as Q-PYTHIA, the splitting functions are directly modified in the medium, this core component remains unchanged in others (e.g. YaJEM).
It has been shown that the shared momentum fraction $z_g$ can be made a Sudakov-safe measurement [1].
This quantity measures the $p_T$ ratio between the two dominant branches
as determined by the SoftDrop grooming process.

We will present the first study of $z_g$ measurements at top RHIC energy in p+p and Au+Au.
The focus will be on the specific di-jet selection introduced in our previous momentum imbalance measurement,
i.e. jets geometrically matched to ``hard core'' jets found using
only constituents above 2 GeV/$c$ and with a high tower above 5.5 GeV [2].
Such di-jet pairs were found to be significantly imbalanced with respect to p+p, yet regained balance when all soft constituents were included.
Individual examination of the splitting behavior of leading and recoil jet adds a new
dimension to this observation, and new input to energy loss models.

[1] A. J. Larkoski, S. Marzani and J. Thaler, Phys. Rev. D 91, no. 11, 111501 (2015) [arXiv:1502.01719 [hep-ph]].

[2] K. Kauder (STAR Collaboration), Nuclear and Particle Physics Proceedings, Hard Probes 2015

Speaker: Kolja Kauder (Wayne State University)

Kolja_Zg_HardProbes_v6.pptx

141 Thermalization and wave turbulence in non-Abelian plasmas

One of the central questions in heavy ion physics is how the deconfined QCD matter produced early in ultra-relativistic heavy ion collisions (HIC) relaxes to thermal equilibrium. This problem proved to be rich, involving a variety of phenomena such as plasma instabilities, chaoticity, turbulence, hydrodynamization in strongly/weakly coupled plasmas, etc.  However, a complete understanding of non-Abelian plasmas dynamics far from thermal equilibrium remains to be achieved.

In classical simulations of anisotropic non-Abelian plasmas that generate plasma instabilities, a stationary power spectrum was observed. This power spectrum was argued to be a result of the turbulent transport of energy from low to large frequencies due to non-linear gluon interactions. However, the fitted spectral exponent -2, could not be understood in the standard framework of (weak) wave turbulence theory which relies on locality of interactions in momentum space. 

In this talk, we argue that due nonlocal interactions in momentum space, local Kolmogorov-Zakharov spectra are not physically relevant. We identify the dominant interactions, namely, small angle soft gluon absorption in the UV, and show how in particular these nonlocal inelastic processes yield a power spectrum with exponent -2 that forms when the system is driven out of equilibrium by injecting energy at a given frequency called the forcing scale. This turbulent spectrum, that agrees with classical YM simulation, is associated to a direct cascade that transports energy toward the UV, that is, above the forcing scale. On the other hand, below the forcing scale, a thermal bath forms quickly, although the system is out of equilibrium. 

As a consequence of nonlocality of interactions, wave turbulence in non-Abelian plasmas exhibits a dual nature and appears to be quite different from Kolmogorov turbulence. This preliminary study might help better understand early time thermalization in heavy ion collisions.

Speaker: Yacine Mehtar-Tani (INT, University of Washington)

2-3-Mehtar.pdf

142 Flow excited by full jet shower in QGP fluid and its effect on jet shape

The structures of jets in heavy ion collisions are significantly modified by strong interactions with quark-gluon plasma (QGP) during the propagation, i.e., collisional energy loss, transverse momentum broadening and induced parton radiation. Through the collisional energy loss and the transverse momentum broadening of the jets, the energy and momentum are deposited into the QGP and induce flows propagating with the jets. Particles originating from the jet-induced flows are observed as a part of the jet and contribute to the modification of the jet shape in the actual experiments. Studying this contribution is not only important for the precise interpretation of the experimental data but also provides a novel opportunity to investigate the collective response of the QGP.

We study the full jet structure modification in QGP including the effect of the jet-induced flows by using the full jet+hydro model. In the model, we describe the evolution of jets by solving transport equations for the three-dimensional momentum distributions of quarks and gluons contained in the full jet shower[1]. The transport equations cover all the processes of the collisional energy loss, transverse momentum broadening and partonic splittings for all partons within the full jet shower. The evolution of the QGP is described by (3+1)-dimensional ideal hydrodynamic equations with source terms. The source terms transfer the deposited energy and momentum to the QGP fluid and are constructed with the evolving distributions of the partons in jets obtained as solutions of the transport equations. We study the jet shape function in Pb+Pb collisions at the LHC and present the role of the flows in QGP induced by the energy-momentum deposition from the jets.

References:
[1] N. B. Chang and G. Y. Qin, arXiv:1603.01920 [hep-ph].

Speaker: Yasuki Tachibana (Central China Normal University)

tachibana_hp16.pdf

143 Full jet evolution in quark-gluon plasma and nuclear modification of jet structure in Pb+Pb collisions at the LHC

We study the evolution of full jets in quark-gluon plasma (QGP) via solving a set of coupled differential transport equations for the three-dimensional
momentum distributions of quarks and gluons contained in the full jet shower. In our jet evolution equations, we include all partonic splitting processes in the dense nuclear medium. We also include the collisional energy loss and transverse momentum broadening for both leading and radiated partons of the full jets due to elastic collisions with the medium constituents. We keep track of both the energies and the transverse momenta of all partons within the full jet shower, thus the modification of both jet energy and jet structure due to jet-medium interaction can be studied straightforwardly. Combining with realistic (2+1)-dimensional viscous hydrodynamic calculation for the space-time profile of the hot and dense nuclear medium produced in Pb+Pb collisions, we apply our formalism to calculate the nuclear modification of single inclusive jet spectra, and the momentum imbalance of photon-jet and dijet pairs at the LHC. The jet shape (at the partonic level) is also studied for the quenched/modified jets in Pb+Pb collisions at the LHC. We further present detailed studies on the roles of different jet-medium interaction mechanisms on the modification of jet energy and jet structure.

Speaker: Ning-Bo Chang (Central China Normal University)

2-5-Changnb_final.pdf

12:20 Lunch

14:00 Afternoon Excursion

16:00 IAC Meeting

Monday, 26 September

Plenary Session V: Jet quenching I

Convener: Barbara Jacak (Stony Brook University)

144 Parton energy loss in QCD matter-Theory

Speaker: Konrad Tywoniuk (CERN)

1_1_HP2016Wuhan_KT.pdf

145 Jet spectra in pp, pA and AA

Speaker: Kurt Eduard Jung (University of Illinois at Chicago (US))

hp2016_kjung_jetSpec.pdf

146 High pT spectra of light and heavy hadrons & anisotropy

Speaker: Peter Christiansen (Lund University (SE))

p_christiansen_hard_probes_v2.pdf

p_christiansen_hard_probes_v2.pptx

147 Jet shapes and structure

Speaker: Leticia Cunqueiro Mendez (Westfaelische Wilhelms-Universitaet Muenster (DE))

1-4-HardProbes16.pdf

10:30 Break

Plenary Session VI: Jet quenching II

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

148 Modification of jet rate, shape and structure model and phenomenology

Speaker: Guang-You Qin (Central China Normal University)

2_1_Qin_HP2016_v7.pdf

149 High pt correlations

Speaker: Alexander Schmah (Lawrence Berkeley National Lab)

aschmah_HP_2016_V8b.pdf

aschmah_HP_2016_V8b.pptx

150 Flavor aspects of parton energy loss

Speaker: Martin Spousta (Charles University)

2_3_Spousta_HardProbes2016_20150609.pdf

12:30 Lunch

Plenary Session VII: Jet quenching III

Convener: Brian Cole (Columbia University (US))

151 SCET for jet physics in the vacuum and the medium

Speaker: Ivan Vitev (LANL)

1-1-Vitev_HP2016.pdf

152 Resolving R_AA and v_n puzzle

Speaker: Jacquelyn Noronha-Hostler (University of Houston)

HardProbes.pdf

153 Monte Carlo simulations of hard probes

Speaker: Marta Verweij (CERN)

160926_JetQuenchingMCs_v2.pdf

15:30 Break

Plenary Session VIII: Hard probes in p+A collisions

Convener: Yasuyuki Akiba (RIKEN)

154 Hard processes in p+A collisions

Speaker: Francois Arleo (Laboratoire Leprince-Ringuet)

arleo_hp16.pdf

155 Quarkonium production in pp and pA (theory)

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

Ferreiro_HP2016.pptx

156 Evolution equations and factorization in pA collisions

Speaker: Guillaume Beuf (University of Santiago de Compostela)

1-6-GBeuf_HP2016.pdf

18:30 Conference Banquet

Tuesday, 27 September

Plenary Session IX: Heavy Flavors

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

157 HF Experimenta at RHIC

Speaker: Wei Xie (Purdue University)

1-1-talk_Wei_Xie_HP16_v5.pdf

1-1-talk_Wei_Xie_HP16_v5.pptx

158 HF Experiments at LHC

Speaker: Gian Michele Innocenti (Massachusetts Inst. of Technology (US))

HPtalkOriginalInno.pdf

159 Heavy Flavor Theory

Speaker: Marlene Nahrgang

nahrgang_HP2016.pdf

160 Quarkonia experiments in AA collisions

Speaker: Zebo Tang (University of Science and Technology of China)

1-4-ZeboTang_HP2016.pdf

10:30 Break

Plenary Session X: Quarkonia and EM probes

Convener: Itzhak Tserruya (Weizmann Institute of Science (IL))

161 Quarkonia production (theory)

Speaker: Michael Strickland (Kent State University)

strickland.pdf

162 Experiments on Photons and dileptons production

Speaker: Stefan Bathe (Brookhaven National Laboratory (US))

2-2-StefanBatheHP2016.pdf

163 Photons and dileptons production (theory)

Speaker: Jean-Francois Paquet (Stony Brook University)

hard_probes_Wuhan_EM_probes_Paquet_fixed.pdf

12:30 Lunch

Plenary Session XI: Future Experiments

Convener: Zhangbu Xu (Brookhaven National Laboratory)

164 Future experiments

Speaker: Anne Sickles (Brookhaven)

1-1-sickles_092716.pdf

165 CEPC/SPPC: A future high-energy facility in China

Speaker: Manqi Ruan (Chinese Academy of Sciences (CN))

1-2-CEPC_HP2016-v3.pdf

166 4 flash talks

15:30 Break

Plenary Session XII: Summaries

Convener: Andreas Morsch (CERN)

167 Experimental Summary

Speaker: Helen Caines (School of Physics and Astronomy)

2-1-HPSummaryCaines.pdf

168 Theory summary

Speaker: Sangyong Jeon (McGill University)

2-2-Jeon_wuhan_summary_2016.pdf

169 What are missing?

Speaker: Miklos Gyulassy (Columbia University)

MyHP16-vf.pdf

170 Closing