Conveners
Parallel: A2 - Electroweak Probes I
- Dinesh Srivastava (National Institute of Advanced Studies, Bengaluru)
Parallel: B2 - Heavy Flavor II
- Marcelo Gameiro Munhoz (Universidade de Sao Paulo (BR))
Parallel: C2 - Electroweak Probes II
- Alexander Milov (Weizmann Institute of Science (IL))
Parallel: D2 - Heavy Flavor V
- Che-Ming Ko
Parallel: E2 - Electroweak Probes III
- Peter Alan Steinberg (Brookhaven National Laboratory (US))
Parallel: F2 - Jets and High-PT Hadrons VI
- Abhijit Majumder (Wayne state university)
Parallel: G2 - Jets and High-PT Hadrons VIII
- Urs Wiedemann (CERN)
Parallel: H2 - Jets and High-PT Hadrons X
- Brian Cole (Columbia University (US))
Electroweak bosons produced in lead-lead (Pb+Pb) collisions are an excellent tool to constrain initial-state effects which affect the rates of hard-scattering processes in nucleus-nucleus interactions. The production yields of massive electroweak bosons, observed via their leptonic decay channels, offer a high-precision test of the binary collision scaling expected in Pb+Pb and a way to...
We model relativistic heavy-ion collisions with a hydrid dynamical approach which consists of an IP-Glasma initial state followed by a phase modeled by an effective QCD kinetic theory [1]. This then leads into viscous hydrodynamics and finally transport theory (MUSIC + UrQMD) [2]. The system's complete energy-momentum tensor -- including the shear and bulk viscous components -- is followed...
We investigate photon emission at the hadronization stage of high-energy heavy-ion collisions.
According to coalescence/recombination models for hadronization from a quark-gluon plasma (QGP),
quarks and antiquarks closely locating in the phase space are assumed to suddenly form a hadron.
Transition from free quark/antiquark states to hadrons (bound states of quarks or antiquarks) is,...
PHENIX measurements of low $p_T$ direct photons in Au+Au collisions at 200
GeV show large yields that have simultaneously a large anisotropies with
respect to the reaction plane, and that scale with the charged multiplicity
to a power of 5/4, independent of transverse momentum and collision
centrality. Calculations of thermal photon emission fall short in describing
these three features....
Isolated photon production in pp collisions is one of the most clear tests of hard QCD processes and proton structure functions. Their measurement in pA collisions provides the possiblity to check initial geometrical scaling and possible modifications of the nucleon structure function in nuclei. Furthermore, the isolated photons constrain the kinematics of scattered partons and therefore, the...
Three are the mechanisms that influence quarkonium suppression in a medium: screening, thermal decay, and recombination. In recent years, a framework that can treat them consistently at the same time has been put forward, the open quantum system approach. In this talk, we will discuss how the combination of open quantum system and Effective Field Theory techniques are useful to understand...
The yields of bound quarkonium states in heavy-ion collisions provide a powerful tool to probe the dynamics of the hot, dense plasma. These measurements are sensitive to the effects of color screening, color recombination, and possibly to other, new phenomena affecting dynamics of heavy quarks in the QCD medium. In this talk, the ATLAS results on bottomonium nuclear modification factor and...
Heavy quarks are produced in the earliest stages of a nucleus-nucleus collision and therefore are an important tool to study the subsequent high energy-density medium formed in relativistic heavy-ion collisions. Over the last few decades major efforts have been undertaken in order to understand the properties of the quark-gluon plasma (QGP) using quarkonia. The extent of medium modification...
The production of heavy quarkonium in heavy ion collisions has been used as an important probe of the quark-gluon plasma. To describe the in-medium evolution of quarkonium, one has to take into account plasma screening effects and recombination in a consistent way. Many previous studies calculate dissociation rates from QCD but use recombination models that are based on detailed balance or...
In high energy heavy-ion collisions, the strong electromagnetic (EM) fields of the nuclei can produce energetic, high-density photon fluxes, leading to photon-induced interactions. Recently, significant enhancements of $e^{+}e^{-}$ pair and J/$\psi$ production at very low transverse momentum ($p_{T}$) were observed by the STAR [1, 2] and ALICE [3] collaborations in peripheral hadronic A+A...
The CMS Collaboration reports on new differential measurements of $\gamma\gamma \rightarrow \mu^{+}\mu^{-}$ production in PbPb collisions at $\sqrt{s_{\rm NN}}$ = 5.02~TeV, using data collected during the 2018 LHC run with an integrated luminosity of 1.6~nb$^{-1}$. Photon-photon interactions have been observed in hadronic heavy-ion collisions by STAR and ALTAS experiments at very low...
Dielectron production is suggested as an excellent probe of the hot and dense medium created in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can carry the information from the initial to the final stage of a collision. The study of the dielectron mass spectrum could help to disentangle various contributions. In the low mass...
The Glauber modeling plays a key role in centrality-dependent measurements of heavy-ion collisions.
A central input parameter in Glauber models is the inelastic nucleon-nucleon cross section $\sigma_{\rm nn}^{\rm inel}$ which is nearly always taken from proton-proton measurements. At the LHC energies $\sigma_{\rm nn}^{\rm inel}$ depends on the QCD dynamics at small $x$ and low interaction...
The production of low-mass dielectrons is one of the most promising tools for the understanding of chiral symmetry restoration and the thermodynamical properties of the Quark-Gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions. For low invariant masses ($m_{\rm ee} <$ 1.1 GeV/$c^{2}$), the dielectron invariant-mass spectrum is sensitive to the properties of short-lived vector...
The suppression of $J/\psi$ production caused by the color-screening effect in heavy-ion collisions is considered as an evidence of the creation of quark-gluon plasma. To interpret the observed suppression in heavy-ion collisions, a good understanding of its production mechanism in p+p collisions is needed. However, the production of $J/\psi$ in hadronic collisions remains not fully understood...
Using novel lattice (non-relativistic) QCD techniques, we will present results pertaining to the fate of Υ(1S), Υ(2S) and Υ(3S) in QGP. We will present results on how the masses of these states change with temperature, as well as how their spatial sizes change. Finally, we will also show new lattice QCD results on the heavy quark potential from Wilson lines.
We present LHCb results on quarkonia production in proton-lead collisions, using the data collected in 2016 at sqrt(s_NN) = 8.16 TeV. Measurements are performed in the forward rapidity region (pseudorapidity between 2 and 5), covering both forward (pPb configuration) and backward (Pbp configuration) rapidities. Measurements for charmonium states include prompt and from-b-decay components...
LHCb measurements of the electroweak boson production in forward and backward configuration of proton-lead collisions are sensitive to the nPDFs in a unique kinematic domain, allowing to study in a complementary fashion the structure of the nucleus.
In this talk, we present the latest results obtained on the Z production in pPb and Pbp collisions by LHCb, being the most precise measurements...
Muon pairs produced via two-photon scattering processes in hadronic Pb+Pb collisions provide a potentially sensitive electromagnetic probe of the quark gluon plasma.
First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation...
Gauge boson associated with jet production is a perfect channel for jet quenching. Z+jet and $\gamma+$jet correlations have already been investigated by several theory models and experimental groups in both p+p and Pb-Pb collisions at $\sqrt s=5.02$ TeV. However, W+jets are dominated by quark jet and H+jet are mainly gluon jet, the comparison of W+jet and H+jet would provide complementary...
The region of the QCD phase diagram at high $\mu_{\rm B}$ can be accessed by fixed-target experiments working at future or existing facilities providing nuclear beams in the multi-GeV energy range. In particular, the CERN SPS is able to provide high-intensity beams over a wide energy interval ($\sqrt{s_{\rm NN}}$ = 5-17 GeV) that are ideal for the study of rare signals. Recently, an expression...
It is now well established that jet modification is a multistage effect; hence a single model alone cannot describe all facets of jet modification. The JETSCAPE framework is a multistage framework that uses several modules to simulate different stages of jet propagation through the QGP medium. These simulations require a set of parameters to ensure a smooth transition between stages. We fine...
The differential yields of Z bosons decaying to lepton pairs are measured in PbPb collisions collected in 2018 by the CMS experiment at the LHC. The measurement uses 1.8 nb$^{-1}$ of 5.02~TeV data. The yields in various centrality bins are compared to the HG-PYTHIA model, which indicates that geometric and selection biases could be present for peripheral events. In some cases, the...
Jet production and jet substructure modification in heavy-ion collisions have played an essential role in revealing the in-medium evolution of parton showers and the determination of the properties of strongly-interacting matter under extreme conditions. It is imperative to extend these studies to include flavor tagging and to devise observables that are sensitive to the partonic origin of...
Jets in the vacuum correspond to multi-parton configurations that form predominantly via a branching process sensitive to the soft and collinear divergences of QCD. In heavy-ion collisions, energy loss processes, stimulated via interactions with the medium, affect jet observables in a profound way. On the level of Feynman diagrams this can be traced back to the difference of medium...
Recently, a variety of jet shape and substructure measurements in pp and Pb-Pb collisions have provided new insights into the processes of jet fragmentation and the mechanisms of jet interaction with the quark-gluon plasma. Grooming techniques, such as Soft Drop, allow us to access the hard splittings inside a jet by removing soft radiation emitted at large angles. These techniques provide a...
Recent measurements of jet substructure provide insights into how the hard and soft parts of the jets are modified by jet-medium interaction. One can also learn the flavor dependence of jet quenching via comparisons between boson tagged jet, inclusive jet and heavy flavor jet. In this study, with the Linear Boltzmann Transport (LBT) model, we investigate the jet shape, jet splitting function,...
Jet quenching is used to explore the detailed dynamics of QCD at high densities and temperature. In order to study the parton energy loss dependence on the flavor, we measure the b-jet nuclear modification factor with the latest recorded data-sets of pp and PbPb collisions at 5.02 TeV with CMS detector in 2017 and 2018. The higher center-of-mass energy, compared to the previous study at 2.76...
The suppression of high momentum particles in heavy-ion collisions in comparison to elementary reactions is one of the main indications for the formation of a quark-gluon plasma. In recent studies, full jets are being reconstructed and substructure observables are gaining importance in assessing the medium modifications of hard probes. In this work, the effect of the late stage hadronic...
We present the results for PbPb collisions at 2.76 TeV LHC energy from a parton shower integrated with a hydrodynamic evolution. The initial hard (jet) partons are produced along with soft partons in the initial state EPOS approach (EPOS3 model). The EPOS3 initial state typically contains multiple hard scatterings in each event. The soft partons, represented by strings, melt into a thermalized...
Light meson measurements in high-energy proton-nucleus collisions provide a probe to study the physics of strongly interacting matter and the quark-gluon plasma (QGP). In particular, measuring the nuclear modification factor $R_{pA}$, where the particle production in pA is compared to a baseline proton-proton reference which is scaled to account for nuclear geometry, provides important...
The intermediate pT region is ideal for studying hadronization and the
transition from soft to hard physics. Quark mass and flavor are key
ingredients in hadronization as well as elucidating the details of energy
loss mechanisms in the hard sector. For this reason, it is essential to
study a variety of different particle species, and PHENIX is ideally-suited
for many resonance decay...
Interactions between hard partons and the quark-gluon plasma range from frequent soft interactions to rare hard interactions. While it is reasonable that hard interactions can be described perturbatively, soft interactions likely suffer from significant non-perturbative effects. Since the effect of the soft interactions can be encoded into parton transport coefficients, these non-perturbative...
Complementary to jet reconstruction, two-particle correlations in $\Delta\eta$ and $\Delta\varphi$ are used to study jets, and in particular their particle composition. While in Pb-Pb collisions this is done to characterize the quark-gluon plasma, pp and p-Pb collisions serve as a reference and are of interest on their own for their input into the understanding of particle production...
In proton-proton collisions the underlying event is rather well
reproduced by general purpose event generators such as Herwig, Pythia
and Sherpa. The key to this success has been the modelling of
multi-parton interactions (MPI). Since long it has been recognised
that the (semi-) soft partonic sub-scatterings in such a scenario
cannot be treated completely independent and the concept of...
In heavy-ion collisions the Quark Gluon Plasma (QGP) is recreated which is believed to have filled our universe shortly after the Big Bang. The quenching of highly energetic jets which are also produced in these collisions are powerful probes of the QGP. We propose the measurement of leading and subleading jets as a new probe of the underlying dynamics of the QGP. The dynamics of leading jets...
Jet modification is a multi-stage (multi-scale) process: an initial high virtuality stage gives way to a lower virtuality transport stage for high energy partons, and a strongly coupled phase for lower energy parts of the shower. The transition from the high virtuality medium-modified DGLAP stage takes place when the virtuality reaches the medium induced scale $\hat{q} \tau$, where $\tau$ is...
Under the assumption that a quark-gluon plasma droplet is produced in $p$ + A collisions, $\gamma$-triggered hadron spectra [1,2] are studied within a next-to-leading-order perturbative QCD parton model with the medium-modified parton fragmentation functions in $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The initial conditions and space-time evolution of the small system of hot and...
