Quark Matter 2015 - XXV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

Sep 27, 2015, 8:00 AM → Oct 3, 2015, 6:00 PM Japan

Kobe, Fashion Mart, Japan

Hideki Hamagaki (University of Tokyo (JP)), Tetsuo Hatsuda (Unknown), Yasuyuki Akiba (RIKEN)

The Quark Matter 2015 is the XXV international conference on ultrarelativistic heavy-ion collisions. The aim of this conference is to unravel mystery of strongly interacting matter at extreme environments created in the ultrarelativistic heavy-ion collisions, in early universe, and in the central core of superdense stars. Both the theoretical and experimental physicists from all over the world get together for every 1.5 years to exchange information on the forefront researches in this field and related subjects. Following the previous Quark Matter conference in Darmstadt, Germany in 2014, the current meeting will be held in Kobe, Fashion Mart, Japan on September 27th to October 3rd in 2015.

All-in-one_Booklet_9.23_v2.pdf

All-Sessions[Chair-TK-MR]_9.23.2015.pdf

Book_of_abstracts_for_poster_session_20150927a.pdf

List_of_contributed_talk_20150915.pdf

MicRunner_Fellows_by_name_9.23.2015.pdf

MicRunner_Fellows_by_session_9.23.2015.pdf

Parallel-TK_Fellows_9.23.2015.pdf

Plenary-TK_Fellows_9.23.2015.pdf

PosterList_ID_0927a.pdf

PosterList_LastName_0927a.pdf

Quark Matter 2015 Poster QM15poster.pdf

Sunday, September 27

9:00 AM → 4:45 PM Student Day

9:00 AM Theory Overview

I will discuss the basic theory and phenomenology used to describe the physics of heavy ion collisions. This includes the color glass condensate and glasma, viscous fluid dynamics, perturbative methods to describe hard probes and jets, and various aspects of the theory of electromagnetic probes and heavy quarks. This overview cannot be comprehensive but is aimed at introducing the basic concepts.

Speaker: Bjoern Schenke (Brookhaven National Lab)

schenke_QM_Theory.pdf

9:50 AM break

10:00 AM Study of QCD Phase Structure in High-Energy Nuclear Collisions

In this talk we will discuss the recent progresses on the study of phase structure of matter with the QCD degrees of freedom in high-energy nuclear collisions. I will focus on the energy dependence of the measurements of collectivity and high moments from high-energy nuclear collisions.

Speaker: Nu Xu (LBNL)

0927_0_1_NuXu.pdf

10:50 AM break

11:00 AM Flow

The standard model of bulk particle production in nucleus-nucleus collisions involves the formation of a transient fluid. I show that generic patterns are expected on this basis alone, and observed in data. I also define the terminology which is commonly used in talks at Quark Matter conferences.

Speaker: Jean-Yves Ollitrault (CNRS)

QM2015_Ollitrault.pdf

11:50 AM Q & A session - I

12:15 PM Lunch

1:30 PM QCD in heavy ion collisions

I will make an overview of the theoretical side of the beam-energy scan program in the context of the QCD phase diagram. I will clarify what is established about hot and dense matter of QCD (especially about the chemical-freezeout curve) and what still awaits further investigations including the modern lattice-QCD simulations. I also briefly mention on the initial dynamics of the heavy-ion collision and the theoretical foundation and some ongoing experimental efforts to see chiral-anomaly related phenomena.

Speaker: Kenji Fukushima (The University of Tokyo)

fukushima.pdf

2:20 PM break

2:30 PM Hard Probes of Hot Matter

In this lecture I will discuss some of the basic considerations in the study of "hard probes" in nuclear collisions from an experimentalists point of view. The lecture will cover four aspects: What are hard probes and why are we interested in them? How do we detect these probes in experiment? What have we learned about QGP and its effects on hard probes? What are the prospects for QGP microscopy using hard probes?

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

0927_0_1_Roland.pdf

3:20 PM break

3:30 PM Experiment overview and perspectives

Speaker: Barbara Jacak (Lawrence Berkeley National Lab. (US))

0927_0_1_Jacak.pdf

0927_0_1_Jacak.pptx

4:20 PM Q & A session - II

4:30 PM → 8:00 PM Check In

4:30 PM → 8:00 PM Welcome Drink

Monday, September 28

8:00 AM → 9:00 AM Check In

9:00 AM → 9:30 AM Opening Ceremony

Convener: Yasuyuki Akiba (RIKEN (JP))

9:00 AM Welcome by Hideki Hamagaki, Chair of the QM2015 Conference

9:04 AM Welcome by Yasuhiko Fujii, President of the Japanese Physical Society

9:09 AM Welcome by Kumie Inose, Vice-President of Science Council of Japan

9:14 AM Welcome by Kizo Hisamoto, Mayor of Kobe

9:19 AM Welcome by Takaharu Otsuka, Director of the Center for Nuclear Study, The Univ. of Tokyo

9:24 AM Welcome by Hideto En'yo, Director of the RIKEN Nishina Center

9:29 AM Message by Shinzo Abe, Prime Minister of Japan (to be read by Yasuyuki Akiba, RIKEN)

9:30 AM → 10:15 AM Opening Talk

Convener: Yasuyuki Akiba (RIKEN (JP))

9:30 AM Ultrarelativistic heavy ion collisions: the first billion seconds

Speaker: Gordon Baym (University of Illinois)

BAYM-QM2015F.pdf

10:15 AM → 10:40 AM Teaser Talks

Convener: Yasuyuki Akiba (RIKEN (JP))

10:15 AM ALICE

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

ALICE-QM2015-Flash.pdf

10:20 AM ATLAS

Speaker: Adam Trzupek (Institute of Nuclear Physics Polish Academy of Sciences (PL))

ATLAS_flash1.pdf

10:25 AM CMS

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

20150928-QM2015_yenjie-v11.pdf

10:30 AM PHENIX

Speaker: David Morrison (BNL)

PHENIX_QM_teaser.mp4

10:35 AM STAR

Speaker: Frank Geurts (Rice University (US))

QM2015_geurts-final.pdf

QM2015_geurts-final.pptx

10:40 AM → 11:15 AM Coffee break

11:15 AM → 12:55 PM Quarkonia I

Convener: Thomas Peitzmann (Utrecht University (NL))

11:15 AM Quarkonium production in proton-proton and proton-lead collisions with ATLAS at the LHC

The suppression of heavy quarkonium states such as J/psi, psi(2S) and Upsilon(nS) in heavy-ion collisions, with respect to proton-proton collisions, plays an important role in studying the hot and dense medium formed in the larger collision systems. A full assessment of this suppression requires understanding of nuclear effects which may affect the production of quarkonium states even in the absence of the medium. The study of quarkonium production in proton-nucleus collisions serves as a baseline for understanding heavy-ion collisions and furthers our knowledge of such nuclear effects. Using proton-lead and proton-proton collision data collected at the LHC in 2013, the ATLAS experiment measures J/psi, psi(2S) and Upsilon(nS) production. The yields of charmonium states are separated into contributions from b-hadron decays and prompt production. The nuclear modification factors and excited-to-ground state ratios are presented. All quarkonium states are reconstructed via the dimuon decay channel and the yields are shown differentially in intervals of transverse momentum, rapidity and event activity.

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

ATLAS_Onia_QHU.pdf

11:35 AM J/psi and psi(2S) production in p-Pb collisions with ALICE at the LHC

The ALICE Collaboration has studied the inclusive $\mathrm{J}/\psi$ and $\psi(\mathrm{2S})$ production in p-Pb collisions at the nucleon-nucleon centre of mass energy $\sqrt{s_{NN}}=5.02$ TeV at the CERN LHC. The strongly bound $\mathrm{J}/\psi$ and the loosely bound $\psi(\mathrm{2S})$ are detected through their decays to muon pairs in two configurations with inverted beam directions, with the following rapidity coverages:$-4.46 < y_{cms} < -2.96$ (Pb-going direction) at backward rapidity and $2.03 < y_{cms} < 3.53$ (p-going direction) at forward rapidity. The $\mathrm{J}/\psi$ production is also studied in the mid-rapidity interval $-1.37 < y_{cms} < 0.43$ in the dielectron decay channel. The $\mathrm{J}/\psi$ and $\psi(\mathrm{2S})$ nuclear modification factors, $R_{pA}$, will be presented as a function of transverse momentum, rapidity and collision centrality; the $\mathrm{J}/\psi$ forward-to-backward ratios and the average $p_{T}^2$ values will be also reported. Notably, the $\psi(\mathrm{2S})$ suppression is larger than the one observed for the $\mathrm{J}/\psi$ and is not described by theoretical models including only nuclear shadowing and coherent energy loss as cold nuclear matter effects. Moreover, results show that the relative $\psi(\mathrm{2S})$ suppression relative to $\mathrm{J}/\psi$ grows towards central collisions (especially at backward rapidity). We will also show the $\psi(\mathrm{2S})$/$\mathrm{J}/\psi$ ratio as a function of transverse momentum, rapidity and centrality. Our measurements will be discussed together with results of recent theoretical calculations.

Speaker: Marco Leoncino (University of Turin and INFN (IT))

Leoncino_QM15.pdf

11:55 AM LHCb results from proton ion collisions

Proton-lead and lead-proton data taking during 2013 has allowed LHCb to expand its core physics program into the regime of heavy ion physics. Results include the first forward measurement of Z production in proton-lead collisions as well as a measurement of the nuclear modification factor and forward-backward production of prompt and displaced J/psi, psi(2S) and Upsilons. Angular particle correlations have also been measured for events of varying charged particle activity.

Speaker: Zhenwei Yang (Tsinghua University (CN))

QM2015_lhcb_Zhenwei_final_20150928.pdf

12:15 PM Cold Nuclear Matter Effects on J/psi and Upsilon production in p+Pb collisions at 5 TeV and Pb+Pb collisions at 5.1 TeV

We make a systematic study of the modifications of $J/\psi$ and $\Upsilon(1S)$ production in $p+$Pb collisions at $\sqrt{s_{_{NN}}} = 5$ TeV at the LHC. We compare the uncertainties in the EPS09 shadowing parameterization to the calculated mass and scale uncertainties obtained employng the EPS09 NLO central set. We study the dependence of the results on the proton parton density and the choice of the nuclear modifications. We check whether the results obtained are consistent at leading and next-to-leading order. The calculations are compared to the available ALICE and LHCb data on the nuclear modification factors, $R_{pA}(y)$ and $R_{pA}(p_T)$, as well as the forward-backward asymmetries, $R_{FB}(y)$ and $R_{FB}(p_T)$. Finally, we make predictions for the next Pb+Pb run at $\sqrt{s_{_{NN}}} = 5.1$ TeV in Run 2 of the LHC.

Speaker: Ramona Vogt (LLNL and UC Davis)

qm15_talk.pdf

12:35 PM Forward $J/psi$ production in pA collisions at the LHC

Inclusive production of $J/\psi$ mesons, especially at forward rapidities, is an important probe of small-x gluons in protons and nuclei. In this work we re-evaluate the production cross sections in the Color Glass Condensate framework, where the process is described by a large x gluon from the probe splitting into a quark pair and eikonally interacting with the target proton or nucleus. Using a standard collinear gluon distribution for the probe and an up to date dipole cross section fitted to HERA data to describe the target we achieve a rather good description of the cross section in proton-proton collisions, although with a rather large normalization uncertainty. More importantly, we show that generalizing the dipole cross section to nuclei in the Glauber approach results in a nuclear suppression of $J/\psi$ production that is much closer to the experimental data than claimed in previous literature.

Speaker: Bertrand Ducloue

QM2015_Ducloue.pdf

11:15 AM → 12:55 PM New Theoretical Development I

Convener: Chihiro Sasaki (FIAS & Uni of Wroclaw (DE))

11:15 AM Chiral Kinetic Theory

A significant body of recent research is aimed towards understanding the anomalous parity-odd response of chiral media, such as chiral magnetic and vortical effects, with applications to heavy-ion collisions and Dirac semimetals. Remarkable progress has been achieved in the non-equilibrium kinetic approach to such phenomena. The chiral kinetic theory features novel properties implementing non-trivially the physics of quantum anomaly and Lorentz invariance. Based on: PRL 109(2012)162001; PRL 113(2014)182302; PRL 115(2015)021601.

Speaker: Misha Stephanov (UIC)

stephanov-qm-2015.pdf

11:35 AM Chiral drag force

We provide a holographic evaluation of novel contributions to the drag force acting on a heavy quark moving through strongly interacting plasma. The new contributions are chiral in that they act in opposite directions in plasmas containing an excess of left- or right-handed quarks and in that they are proportional to the coefficient of the axial anomaly. These new contributions to the drag force act either parallel to or antiparallel to an external magnetic field or to the vorticity of the fluid plasma. In all these respects, these contributions to the drag force felt by a heavy quark are analogous to the chiral magnetic effect on light quarks. However, the new contribution to the drag force is independent of the electric charge of the heavy quark and is the same for heavy quarks and antiquarks. We show that although the chiral drag force can be non-vanishing for heavy quarks that are at rest in the local fluid rest frame, it does vanish for heavy quarks that are at rest in a frame in which there is no local entropy current. In this frame, the heavy quark at rest sees counterpropagating momentum and charge currents, both proportional to the axial anomaly coefficient, but feels no drag force. This provides strong concrete evidence for the absence of dissipation in chiral transport, something that has been predicted previously via consideration of symmetries. Along the way to our principal results, we provide a general calculation of the corrections to the drag force due to the presence of gradients in the flowing fluid in the presence of a nonzero chemical potential. We close with a consequence of our result that is at least in principle observable in heavy ion collisions, namely an anticorrelation between the direction of the CME current for light quarks in a given event and the direction of the kick given to the momentum of all the heavy quarks and antiquarks in that event.

Speaker: Andrey Sadofyev (Massachusetts Inst. of Technology (US))

QM2015_AS.pdf

11:55 AM Third order relativistic dissipative fluid dynamics in heavy-ion collisions and astrophysics

The development of relativistic dissipative fluid dynamics is a very important scientific achievement of the last two decades. It has inspired many authors to apply its methodology to lots of possible applications in physical problems. For example it allows to derive hydrodynamical like equations for relativistic heavy-ion collisions, astrophysics, cosmology and plasma physics. So far a symmetric hyperbolic system of evolution equations for the independent field variables has been obtained up to second order with respect to thermodynamic equilibrium. However the exploitation to third order is desirable in order to study the couplings between the three major dissipative fluxes which contribute to the entropy generation in a single-component fluid. In this paper the development of relativistic fluid dynamics is carried through to third order with respect to thermodynamic equilibrium. The set of obtained field equations is closed by imposing the relativity principle and the entropy principle up to third order. Imposing these conditions up to third order affects and restricts the lower order terms. This, in turn, affects the equilibrium expressions which are already explicitly known.

Speaker: Azwinndini Muronga (University of Johannesburg)

0928_2_2_3_Muronga.pdf

12:15 PM Hydrodynamics with chiral anomaly and charge separation in relativistic heavy ion collisions

Chiral Magnetic Effect (CME) is a phenomenon that for systems with chiral fermions, in the presence of external magnetic field and chirality imbalance, a charge current is generated along the magnetic field direction. The CME predicts that for quark-gluon plasma (QGP) created in relativistic heavy ion collisions, there would be a charge separation perpendicular to the collisional reaction plane. Charge correlation measurements designed for the search of such signal have been done at RHIC and the LHC for which the interpretations, however, remain unclear due to contamination by background effects that are collective flow driven, theoretically poorly constrained, and experimentally hard to separate. Using anomalous (and viscous) hydrodynamic simulations, we make a first attempt at quantifying contributions to observed charge correlations from both CME and background effects in one and same framework. The implications for the search of CME are discussed.

Speaker: Xu-Guang Huang (Fudan University)

x.g.huang.pdf

12:35 PM What flows in the chirally anomalous transport?

The chirally anomalous transport including the chiral magnetic effect seems to get established from the theoretical side, but some theorists address serious concerns about the physical interpretation of $\langle\Omega|\boldsymbol{j}|\Omega\rangle$. In my talk I will emphasize how the conventional scenario can be verified from the dynamical process of the particle production. If $|\Omega\rangle$ is an equilibrated static state, a current which is a real-time phenomenon, cannot flow and $\langle\Omega|\boldsymbol{j}|\Omega\rangle$ is not a current but should be a polarization. Such an interpretation is manifest for the chiral separation effect. Besides, in a quick derivation of the chiral magnetic effect using the Chern-Simons-Maxwell theory, the anomalous current appears in the same way as the Maxwell's displacement current, and we all know that the displacement current is a source of the magnetic field but there is no flow of electric carriers. Logically, it is possible that $\langle\Omega|\boldsymbol{j}|\Omega\rangle$ is also such a current containing no flow of charged particles, which is actually the case if the chiral magnetic current is formulated in the chiral perturbation theory. I would however, emphasize that the genuine current generation occurs at the same time as the particle production with glasma flux tubes that locally violate P- and CP-symmetries together with an external magnetic field. The distribution function in momentum space is dynamically determined by microscopic processes of the particle production and I will present some results from the numerical simulation. A non-trivial observation found in the numerical simulation includes a quantitative estimate of the response time of the system until the anomalous current starts growing up after the switch-on of the background fields, which has a practically important implication for the detection of the physical observables sensisive to the chrally anomalous transport in experiments.

Speaker: Kenji Fukushima (The University of Tokyo)

fukushima.pdf

11:15 AM → 12:55 PM Open Heavy Flavors and Strangeness I

Convener: Yu-Gang Ma (Shanghai Institute of Applied Physics, Chinese Academy of Sciences (CN))

11:15 AM Identified light and strange hadron spectra at $\sqrt{s_{NN}}$=14.5~GeV and systematic study of baryon/meson effect at intermediate transverse momentum with STAR at RHIC BES I

With the recently measured Au$+$Au collisions at $\sqrt{s_{NN}}$= 14.5~GeV, STAR completed its first phase of the Beam Energy Scan (BES) program at RHIC. The main motivation of the BES program is the study of the QCD phase diagram and the search for a conjectured critical point. Amongst the various collision energies of 7.7, 11.5, 19.6, 27, and 39~GeV, that have been previously presented by STAR, collisions at 14.5~GeV will provide data set in the relatively large chemical potential gap between the 11.5 and 19.6~GeV center-of-mass energies. In this contribution, we report new STAR measurements of Au$+$Au at $\sqrt{s_{NN}}$=14.5~GeV that involve identified light particle R$_{CP}$ and spectra, as well as measurements of the strange hadrons ($K^0_{s}$, $\Lambda$, $\Xi$, $\Omega$ and $\phi$). The spectra from both light and strange particles cover a significant range of the intermediate transverse momentum (2 $<p_T<$ 5~GeV/c) in all beam energies. This provides a unique set of data for a systematic study of the baryon-to-meson ratio at intermediate $p_T$ from BES Phase I. We will discuss its physics implications and whether hadronic interactions at late stage dominate the collision dynamics.

Speaker: James Brandenburg (Rice University)

QM_2015_Brandenburg_v9.pdf

QM_2015_Brandenburg_v9_ppt.ppt

11:35 AM Multiplicity and rapidity dependence of strangeness and multi-strangeness production in pp, pPb and PbPb at CMS

Measurements of transverse momentum ($p_T$) spectra for strange ($K^0_s$ and $\Lambda$) and multi-strange ($\Xi^-$) hadrons are presented over a wide range of multiplicity and particle rapidity in pp, pPb and PbPb collisions. The data were recorded using the CMS detector at the LHC, with an implementation of high-multiplicity triggers for pp and pPb collision data. The particle ratios, the total strangeness yields and average $p_{T}$ of particle spectra for each species are extracted as a function of multiplicity and compared among different collision systems. Motivated by collective flow phenomena from a fluid-like QGP system, a blast-wave model is employed to explore the system size dependence of radial flow strength among various systems. Furthermore, the wide acceptance coverage of the CMS detector enables a study on rapidity dependence of strange particle $p_{T}$ spectra, especially in asymmetric high-multiplicity pPb collisions, which places stringent tests on theoretical models interpreting particle production mechanism in these collisions. The new results presented provide key insights to understand the underlying dynamics in high-multiplicity small systems.

Speaker: Hong Ni (Vanderbilt University (US))

QM2015_hong_v4.pdf

11:55 AM $\phi$ production at forward rapidity in pp, pPb and PbPb collisions with ALICE

Light vector meson ($\rho$, $\omega$, $\phi$) production provides key information on the hot and dense state of strongly interacting matter produced in high-energy heavy-ion collisions. In particular, strangeness production can be accessed through the measurement of the $\phi$ meson, while the detailed description of the full dimuon mass spectra can be used to reveal in-medium modifications of hadron properties and thermal emission arising from the medium. The detection of vector mesons through their decay in dileptons has the advantage, with respect to hadronic channel, that the decay products are not affected by final state interactions. Measurements in pp and p-A systems, where hot nuclear matter effects are not expected, are used as a reference. The ALICE experiment at the LHC can access vector mesons produced at forward rapidity through their decays in muon pairs. We present results on vector meson production in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$~TeV. In pp collisions the $\phi$ differential cross section as a function of $p_\mathrm{T}$ was measured in the range $1 \le p_\mathrm{T}\ 5 $ GeV/$c$ and compared with the calculations from PHOJET and PYTHIA. In p-Pb collisions, measurements of the $\phi$ yield and the nuclear modification factor in the rapidity ranges $2.03 \le y \le 3.53$ (p-going direction) and $-4.46 \le y \le -2.96$ (Pb-going direction) are shown. An asymmetry between the cross section at forward and backward rapidity is observed. Results are compared to the predictions provided by commonly used event generators. In Pb-Pb collisions, the $\phi$ yield and the nuclear modification factor are obtained as a function of centrality in the intermediate $p_{\rm T}$ region ($2 \le p_{\rm T} \le 5$ GeV/$c$) and for $2.5 \le y \le 4$. Differences are observed between these results and those measured in the same $p_\mathrm{T}$ range at midrapidity in the KK channel.

Speaker: Alessandro De Falco (Universita e INFN (IT))

adf-qm15.pdf

12:15 PM Violation of mass ordering for multi-strange hadrons at RHIC and LHC

We study effects of hadronic rescattering on final observables for multi-strange hadrons in high-energy nuclear collisions within an integrated dynamical model. We simulate the whole collision process on an event-by-event basis by using a fully (3+1)-dimensional ideal hydrodynamic description for the quark gluon plasma (QGP) and a subsequent kinetic transport description for the hadron resonance gas. The QGP created in a collision expands, cools down and then turns into hadron gas. In the last stage of the collisions, hadrons continue to scatter with each other. Therefore observed hadron spectra are, in general, contaminated by the hadronic rescatterings. In order to probe the QGP more directly, multi-strange hadrons, in particular $\phi$-meson and $\Omega$-baryon, can be utilized since multi-strange hadrons have small scattering cross-sections and less scatter with non-strange hadrons. Thus final observables of $\phi$-mesons and $\Omega$-baryons are expected to reflect the properties of the system just after hadronization. Some years ago, violation of mass ordering in $v_2(p_{\rm T})$ was predicted by using a hydro + cascade hybrid model and thereafter observed by the STAR collaboration. Following this work, we scrutinize multi-strange hadron spectra at both RHIC and LHC energies by using a more sophisticated integrated dynamical model towards comprehensive understanding of this phenomenon. In addition to $v_2(p_{\rm T})$, we investigate the hadronic rescattering effects on mean transverse momenta ($\langle p_{\rm T} \rangle$) and $p_{\rm T}$-averaged $v_2$ of hadrons including heavier multi-strange hadrons such as $\Xi$- and $\Omega$-baryons. We also discuss the collision energy dependence of the hadronic rescattering effects on the violation of mass ordering behavior and show that multi-strange hadrons can be used as “penetrating probes” of the QGP.

Speaker: Shiori Takeuchi (Sophia Univ)

QM2015_takeuchi.pdf

12:35 PM Results from (anti-)(hyper-)nuclei production and searches for exotic bound states with ALICE at the LHC

The high collision energies reached at the LHC enable significant production rates of light (anti-)(hyper-)nuclei in proton-proton, proton-lead and, in particular, lead-lead collisions. The excellent particle identification capabilities of the ALICE apparatus, based on the specific energy loss in the time projection chamber and the velocity information from the time-of-flight detector, allow for the detection of these (anti-)nuclei. Furthermore, the high tracking resolution provided by the inner tracking system enables the separation of primary nuclei from those coming from the decay of heavier systems. This allows for the reconstruction of decays such as the hypertriton mesonic weak decay ($^3_{\Lambda}$H $\rightarrow ^3$He + $\pi^-$), the decay of a hypothetical bound state of a $\Lambda$ with a neutron into a deuteron and pion or the H-dibaryon decaying into a $\Lambda$, a proton and a $\pi^{-}$. Results on the production of stable nuclei and anti-nuclei in Pb--Pb and lighter collision systems will be presented. Hypernuclei production rates in Pb--Pb will also be shown, together with upper limits estimated on the production of hypothetical exotica candidates. The results will be compared with predictions for the production in thermal (statistical) and coalescence models.

Speaker: Natasha Sharma (University of Tennessee (US))

Natasha-NucleiQM2015.pdf

11:15 AM → 12:55 PM QCD at High Temperture

Convener: Frithjof Karsch (Brookhaven National Laboratory (US))

11:15 AM Recent progress in understanding gauge topology, confinement and chiral symmetry breaking

Instantons for a long time were associated with breaking of U(1) and SU(Nf) chiral symmetries in QCD-like theories. Monopoles, on the other hand are related to dual superconductor picture and confinement. Instanton-dyons are instanton constituents, discovered in 1998 by van Baal and others: they incorporate properties of both instants and monopoles. Recently several papers, both analytic and numerical simulations, have studied ensemble of the instanton-dyons. The results indeed show that in this way one can explain BOTH confinement and chiral symmetry breaking, when the ensemble is dense enough (at strong enough coupling or small temperature). The details can be found in the references below. Interacting Ensemble of the Instanton-dyons and Deconfinement Phase Transition in the SU(2) Gauge Theory Rasmus Larsen, Edward Shuryak (SUNY, Stony Brook). Apr 13, 2015. 11 pp. e-Print: arXiv:1504.03341 Confining Dyon-Anti-Dyon Coulomb Liquid Model I Yizhuang Liu (Stony Brook U.), Edward Shuryak, Ismail Zahed (SUNY, Stony Brook). Mar 10, 2015. 17 pp. e-Print: arXiv:1503.03058 Light Quarks in the Screened Dyon-Anti-Dyon Coulomb Liquid Model II Yizhuang Liu, Edward Shuryak, Ismail Zahed (SUNY, Stony Brook). Mar 31, 2015. 16 pp. e-Print: arXiv:1503.09148

Speaker: Rasmus Larsen (Stony Brook University)

QM_Talk.pdf

11:35 AM The topological structures in strongly coupled QGP with chiral fermions on the lattice

The nature of chiral phase transition for two flavour QCD is an interesting but unresolved problem. One of the most intriguing issues is whether or not the anomalous U(1) symmetry in the flavour sector is effectively restored along with the chiral symmetry. This may determine the universality class of the chiral phase transition. Since the physics near the chiral phase transition is essentially non-perturbative, we employ first principles lattice techniques to address this issue. We use overlap fermions, which have exact chiral symmetry on the lattice, to probe the anomalous U(1) symmetry violation of 2+1 flavour dynamical QCD configurations with domain wall fermions. The latter also optimally preserves chiral and flavour symmetries on the lattice, since it is known that the remnant chiral symmetry of the light quarks influences the scaling of the chiral condensate [1] in the crossover transition region. We observe that the anomalous U(1) is not effectively restored in the chiral crossover region. This effectively means that the eta' excitations remains distinct from the pion excitations well into the QGP medium. We perform a systematic study of the finite size and cut-off effects since the signals of U(1) violation are sensitive to it. We also provide a glimpse of the microscopic topological structures of the QCD medium that are responsible for the strongly interacting nature of the quark gluon plasma phase. We study the effect of these microscopic constituents through our first calculations for the topological susceptibility of QCD at finite temperature, which could be a crucial input for the equation of state with a finite chiral chemical potential. Reference: [1] S. Ejiri et. al., Phys. Rev. D 80, 094505 (2009).

Speaker: Dr Sayantan Sharma (BNL)

ssharma_qm15.pdf

11:55 AM QCD phase diagram from analytical continuation

We extrapolate the QCD cross-over temperature from imaginary to real chemical potentials. Our calculations are based on new continuum extrapolated lattice simulations using the 4stout staggered actions with a lattice resulution up to Nt=16. The simulation parameters are tuned so that the strangeness neutrality is maintained, as it is in a heavy ion collision. We see a consistency between the Taylor expansion and the analytical continuation method. We also use the lattice data to extrapolate the equation of state to real chemical potentials.

Speaker: Szabolcs Borsanyi (University of Wuppertal)

qm15_analytic.pdf

12:15 PM Energy loss and shear viscosity at NLO in a high-temperature QGP

We present a set of kinetic equations which extend the AMY energy loss formalism to NLO in the strong coupling constant. A novel aspect of the NLO analysis is a consistent description of wider-angle bremsstrahlung (semi-collinear emissions) which smoothly interpolates between 2to2 scattering and collinear bremsstrahlung. Similarly, the NLO treatment describes how the soft collinear emissions can be incorporated into the drag coefficient at NLO. We describe how many of the ingredients of the NLO transport equations (such as the drag coefficient) can be computed using a Euclidean formalism pioneered by S. Caron-Huot. In the second part of the talk we show how the same framework can be used to address the shear viscosity at NLO, up to a coefficient which cannot be determined using the Euclidean formalism. By treating this coefficient as an unknown parameter (within an estimated range) we can however estimate the NLO corrections to $\eta$. Refs: J. Ghiglieri, G. Moore, D. Teaney, "Towards the shear viscosity at NLO in high temperature plasmas", in preparation. J. Ghiglieri, G. Moore, D. Teaney, "Energy loss at NLO in high temperature plasmas", in preparation. J. Ghiglieri and D. Teaney, "Parton energy loss and momentum broadening at NLO in high temperature QCD plasmas", arXiv:1502.03730 [hep-ph]. J. Ghiglieri, et al, "Next-to-leading order thermal photon production in a weakly coupled quark-gluon plasma", JHEP 1305, 010 (2013) [arXiv:1302.5970 [hep-ph]].

Speaker: Dr Jacopo Ghiglieri (Universitaet Bern (CH))

ghiglieri_qm15_low.pdf

ghiglieri_qm15.pdf

12:35 PM Confronting fluctuations of conserved charges in central nuclear collisions at the LHC with predictions from Lattice QCD

We construct net baryon number and strangeness susceptibilities as well as correlations between electric charge, strangeness and baryon number from experimental data on the particle production yields at midrapidity of the ALICE Collaboration at CERN. The data were taken in central Pb-Pb collisions at √sNN=2.76 TeV and cover one unit of rapidity. The resulting fluctuations and correlations are consistent with Lattice QCD results at the chiral crossover pseudocritical temperature Tc ≃ 155 MeV. This agreement lends strong support to the assumption that the fireball created in these collisions is of thermal origin and exhibits characteristic properties expected in QCD at the transition from the quark gluon plasma to the hadronic phase. Since Lattice QCD calculations are performed at a baryochemical potential of mu$_B$ = 0, the comparisons with LHC data are the most direct due to the vanishing baryon transport to midrapidity at these high energies. As an outlook, we will also present the applicability of our approach to RHIC data thus extending the comparisons to non-zero baryochemical potentials.

Speaker: Alexander Philipp Kalweit (CERN)

FluctuationsAkalweit.pdf

FluctuationsAkalweit_v2.pdf

12:55 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Correlations and Fluctuations I

Convener: Tapan Nayak (Department of Atomic Energy (IN))

2:30 PM Higher moments of net-proton and net-charge multiplicity distributions at 14.5 GeV measured in Au+Au collisions at mid-rapidity with STAR at RHIC

Studying fluctuations of conserved quantities, such as baryon number (B) and charge (Q), provides insight into the properties of matter created in high-energy nuclear collisions. Lattice QCD calculations suggest that higher moments of these quantities are sensitive to the phase structure of the hot and dense nuclear matter created in such collisions. The Beam Energy Scan (BES)-I program at RHIC, spanning center-of-mass energies of $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV of Au+Au collisions, provided measurements at different baryochemical potentials, µB, to map the QCD phase diagram. In the years 2010 and 2011, STAR collected data of Au+Au collisions at 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV, leaving a wide gap of about $\mu_{\rm B}$ ~110 MeV between 19.6 ($\mu_{\rm B}$ ~206 MeV) and 11.5 GeV ($\mu_{\rm B}$ ~316 MeV). In this talk, we present first experimental results of higher moments and their products of net-charge and net-proton distributions in Au+Au collisions at 14.5 GeV, measured with the STAR detector at RHIC at mid-rapidity and a transverse momentum up to $p_{\rm T}$ = 2 GeV/c. Their pseudo-rapidity and rapidity dependence will be shown as well. The corresponding value of the chemical potential from the top 5% central collisions is about $\mu_{\rm B}$ ~260 MeV, so that these results fill the largest gap of previous measurements, in $\mu_{\rm B}$, to complete the BES I program. Moreover, the energy dependence of higher moments of net-proton distributions in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7 - 200 GeV in a much larger $p_{\rm T}$ range, utilizing the PID capabilities of the Time-of-Flight detector, are shown. Detector effects, including tracking efficiency, are taken into account. Implications of these results will be discussed in light of the recent Lattice QCD calculations.

Speaker: Dr Jochen Thaeder (Lawrence Berkeley National Laboratory)

NetParticle_STAR_JMT_2015-09-28_QM15_Final.pdf

2:50 PM Longitudinal Asymmetry and its Measurable Effects in Pb-Pb Collisions at 2.76 TeV

In a collision of identical nuclei, the extended size and the finite number of nucleons lead to fluctuations in the number of participating nucleons from each nucleus at any impact parameter. This is akin to collisions of unequal-mass nuclei and corresponds to a non-zero momentum of the participant zone in the laboratory frame. Event-by-event fluctuations are estimated by measuring the asymmetry in the energy deposited by spectator neutrons in the zero-degree calorimeters on either side of the interaction vertex. The effect of these fluctuations on the pseudorapidity distributions of produced particles in Pb-Pb collisions at 2.76 TeV is investigated for the first time. The results from the ALICE detector will be presented for different centralities and compared with results from models.

Speaker: Rashmi Raniwala (University of Rajasthan (IN))

LongAsym-RR-QM2015-28092015.pptx

3:10 PM Measurement of the correlation between flow harmonics of different order in lead-lead collisions at sqrt(sNN)=2.76 TeV with ATLAS

ATLAS measurements of correlations between elliptic or triangular flow, vm (m=2,3), and other flow harmonics vn (n=2−5), in Pb+Pb collisions at sqrt(sNN)=2.76 TeV are presented. The vm-vn correlations are measured as a function of centrality, and as a function of varying event-geometry but fixed centrality using the "event-shape" selection technique.  The measurements show that the effects of viscosity in heavy-ion collisions depend only on the collision centrality and not on the collision geometry. These measurements comprehensively demonstrate that a significant fraction of the higher order flow (n>3), is in fact generated from the hydrodynamic response to lower order eccentricities. The separation of the higher order flow harmonics into linear and non-linear components that are directly related to the same- and lower-order eccentricity of the initial geometry is done and their centrality dependence is measured. Comparisons to previous event-plane correlations that probe the non-linear hydrodynamic response are also presented.

Speaker: Sooraj Krishnan Radhakrishnan (State University of New York (US))

qm15_sradhakrishnan.pdf

3:30 PM Thermal blurring effects on fluctuations of conserved charges in rapidity space

We study the effect of the difference between momentum- and coordinate-space rapidities on the experimental measurements of fluctuation observables in relativistic heavy ion collisions. In theoretical studies on fluctuation observables, observables in fixed coordinate-space rapidity windows are concerned because the analyses are usually performed in finite volume. The experimental measurements, however, can be performed only for momentum-space (or pesudo-) rapidity. The latter is usually used as a proxy of the former implicitly. However, thermal motion blurs this one-to-one correspondence. We investigate this effect quantitatively, and show that thermal motion gives rise to significant effects, which should be carefully taken into account in the interpretation of the experimental results of fluctuation observables. It is argued that this modification can be estimated by the study of the rapidity window dependences of the cumulants and implemented in the description of the time evolution of fluctuations.

Speaker: Masayuki Asakawa (Osaka University)

QM2015Asakawa.pdf

3:50 PM Influence of conservation laws on higher moments of the net proton and net charge distribution

The higher moments of the net baryon and net charge distributions, e.g. the skewness and kurtosis, are studied within an infinite hadronic matter calculation in a transport approach. By dividing the box into several parts, the volume dependence of the fluctuations is investigated. After confirming that the initial distributions follow the expectations from a Poisson distribution, the influence of quantum number conservation like the net baryon number and the net charge in the system on the higher moments is evaluated. For this purpose, the composition of the hadron gas is adjusted for different scenarios, only baryons are simulated to study the net baryon conservation or only pions and $\rho$ mesons to investigate the charge conservation effect. In addition, the effect of imposing kinematic cuts in momentum space is analysed. The role of resonance excitations and decays on the higher moments can also be studied within this model. This work is highly relevant to understand the experimental measurements of higher moments obtained in the RHIC beam energy scan and their comparison to lattice results and other theoretical calculations assuming infinite matter.

Speaker: Hannah Petersen

petersen_qm15.pdf

4:10 PM Nonlinear hydrodynamic response confronts LHC data

Higher-order harmonics of anisotropic flow ($v_n$ with $n\ge 4$) can be measured with the direction of lower-order harmonics, e.g., $v_4$ with respect to the $v_2$ plane. We show that one can scale these measurements by quantities involving lower-order harmonics in such a way that the ratio is independent of initial conditions, and solely involves the medium nonlinear response. The resulting ratios allow to directly confront hydrodynamics with experimental data [1]. We construct four independent such ratios involving $v_4$, $v_5$ and $v_6$ and extract their values from LHC data on Pb+Pb collisions, as a function of centrality. We then calculate these ratios using single-shot hydrodynamics and using the transport model AMPT [2]. Model calculations are in very good agreement with data. We point out that hydrodynamics predicts simple scaling relations between these response coefficients, which can be read off directly from data. A substantial response ratio in the seventh harmonic is found in theoretical calculations (both in AMPT and in hydrodynamics), from which we argue that a nonzero $v_7$ signal should be seen when measured with respect to elliptic and triangular flow. We present predictions for $v_7$ versus centrality in Pb+Pb collisions at the LHC. Finally, we point out that combined measurements of higher-order harmonics with their own plane and with respect to lower-order planes can be quantitatively related to event-plane correlations. As an illustration, we show that CMS data on $v_4$ and $v_6$ are compatible with ATLAS data on event-plane correlations. [1] L. Yan and J. Y. Ollitrault, Phys.Lett. B ${\bf 744}$, 82 (2015) [arXiv:1502.02502 [nucl-th]]. [2] L. Yan, S. Pal and J. Y. Ollitrault, in preparation

Speaker: Li Yan (CNRS)

yan_talk.pdf

2:30 PM → 4:30 PM Jets and High pT Hadrons I

Convener: John Harris (Yale University (US))

2:30 PM Charged particle production in proton-lead collisions measured by the ATLAS detector

Measurements of the centrality dependence of low-$p_T$ and high-$p_T$ particle production in proton-lead collisions at the LHC can provide unique insight into the dynamics of soft and hard scattering processes and the initial state of ultra-relativistic nuclear collisions. Recent results have shown that both soft and hard processes may be significantly influenced by event-to-event fluctuations (variations) in the structure of the proton. In this talk, the latest measurements of the centrality dependence of charged particle, jet, and Z boson production with the ATLAS detector at the LHC will be used to explore these questions. In particular, the sensitivity of the charged particle pseudorapidity distribution in proton--lead collisions to the choice of centrality variable will be discussed. Separately, the strong centrality dependence of jet production in proton--lead collisions has raised questions about energy production at large rapidities in collisions involving a large proton-$x$. To address this, measurements of the correlation between the initial-state hard scattering kinematics in dijet events and forward transverse energy in proton-proton collisions will be presented.

Speaker: Evgeny Shulga (National Research Nuclear University MEPhI (RU))

QM15_eshulga_v1.pdf

2:50 PM Decomposing energy balance contributions for quenched jets with CMS

Jet quenching is one of the established signatures of the Quark Gluon Plasma, and this phenomenon has been studied extensively in high energy heavy ion experiments over the last decade. Despite significant progress made in those studies, the specifics of the energy loss mechanisms and the details of jet-medium interactions require further quantitative understanding. Studies of two-dimensional angular correlations of charged hadrons with respect to reconstructed jets make it possible to experimentally assess the energy radiation patterns of an energetic parton traversing the medium as well as its fragmentation function. In this talk, we will present new differential measurements of charged particle densities and energy flow about the jet direction as a function of relative azimuth and relative pseudorapidity from 2.76 TeV PbPb and pp collisions recorded by the CMS Collaboration. With a sample of back-to-back dijets, previously used to reconstruct the event-wise momentum imbalance (missing $p_{T}$), we explore modifications to correlated charged hadron distributions for both the leading and the subleading sides of the dijet. With this technique, we can individually assess the contribution of the medium-induced modifications to each side of the dijet and explore the extent of potential medium response to the jet propagation, while also extending these measurements to large angular and radial distances.

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

2015_QM_Evdokimov_final.pdf

3:10 PM Angular distributions of the quenched energy flow from dijets with different radius parameters in CMS

One of the first observations of the flow of the quenched energy in imbalanced dijet events has been through the studies of transverse vector sum of particles with the CMS detector, namely the missing $p_{T}$ measurement. The results have led to new theoretical insights to order to explain the wide angle radiation, such as "jet collimation", "color decoherence", "turbulence cascade" and "hydrodynamical expansion of quenched energy". These mechanisms could give different angular distribution of quenched energy. In this talk, the missing $p_{T}$ technique has been improved so that it allows the study of angular distribution of the energy flow with respect to the dijet axis. Moreover, in order to get insights about the number of particles which carry the quenched energy, charged particle multiplicity differences in the leading and subleading jet hemispheres are measured. In addition, the measurements are performed using different resolution parameters in anti-$k_{T}$ clustering algorithm, which provide information about how the angular distribution of the quenched energy depends on the jet width.

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

mptTalkQM2015_CFMcGinn_20150928.pdf

3:30 PM Interplay between Mach cone and radial expansion in jet events

As we see expansion of bulk quark-gluon plasma (QGP) created in high-energy nuclear collisions is well described by relativistic hydrodynamics, fluidity is one of the key properties of the QGP. At the same time, the QGP has a large stopping power against propagation of jets: The jets lose a large amount of their energies while traversing the QGP fluid due to strong interactions between them. The deposited energy of the jet induces a shock wave, a.k.a. Mach cone, in the QGP as a hydrodynamic response. Such a hydrodynamic response is also a clear manifestation of the fluidity of the QGP. Since the structure of shock wave is characterized by various properties of the QGP, e.g., sound velocity, stopping power, and viscosity, we have a great opportunity to extract the property of the QGP by analyzing this phenomenon. We study the hydrodynamic response to jet propagation in the expanding QGP and investigate how it reflects the particle spectra after the hydrodynamic evolution of the bulk QGP. We perform simulations of the bulk dynamics of the QGP specifically in di-jet and gamma-jet events by solving (3+1)-dimensional ideal hydrodynamic equations with source terms. Mach cones are formed and largely develops in the QGP fluid. However, the double peak in the azimuthal particle distribution, which is believed to be an intuitive signal of the Mach cone, is smeared out by the diffusion wake, the distortion by the radial flow and freeze-out processes. Instead, we find a novel phenomenon of the interplay between the Mach cone and radial expansion when the jets travel through the off-central trajectories: Propagation of Mach cone pushes back the radial flow. As a result, the particle production is suppressed in the direction perpendicular to the jet propagation. This is the direct signal of hydrodynamic response to jet propagation and even includes the information about the jet passage in the expanding QGP fluid.

Speaker: Dr Yasuki Tachibana (Nishina Center, RIKEN)

tachibana_qm15.pdf

3:50 PM Thermalization of mini-jets in a quark-gluon plasma

We complete the physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma by investigating the thermalization of the soft components of the jet. We argue that the following scenario should hold: the leading particle emits a significant number of mini-jets which promptly evolve via quasi-democratic branchings and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature T. Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equilibrium with the plasma over a time scale which is considerably shorter than the typical lifetime of the mini-jet. The thermalized gluons form a tail which lags behind the hard components of the jet. We support this scenario, first, via parametric arguments and, next, by studying a simplified kinetic equation, which describes the jet dynamics in longitudinal phase-space. We solve the kinetic equation using both (semi-)analytical and numerical methods. In particular, we obtain the first exact, analytic, solutions to the ultrarelativistic Fokker-Planck equation in one-dimensional phase-space. Our results confirm the physical picture aforementioned and demonstrate the quenching of the jet via multiple branching followed by the thermalization of the soft gluons in the cascades.

Speaker: Bin Wu (CEA-Saclay)

jetTherm.pdf

4:10 PM Modification of reconstructed gamma-jets in heavy-ion collisions

We use the Linear Boltzmann Transport model for jet propagation to study gamma-triggered jets in high-energy heavy-ion collisions. Since recoiled partons from both elastic scattering and induced gluon radiation processes and their further propagation are specifically considered, the simulations can provide a realistic description of not only the medium modification of the reconstructed jets but also the energy flow in the underlying hydrodynamic background. In this talk, we will discuss the energy flow of the jet-induced medium excitation. By subtracting the same 3+1D hydrodynamic background without gamma-jets, we can calculate the azimuthal angular distribution of both soft and hard particles respect to the triggered gamma and the reconstructed jets. We also show the sensitivity of such angular distributions to the jet-medium interaction strength in particular the jet transport parameters within the LBT model. [1] Y. He, T. Luo, X. N. Wang and Y. Zhu, Linear Boltzmann Transport for Jet Propagation in the Quark-Gluon Plasma: Elastic Processes and Medium Recoil, Phys. Rev. C 91, 054908 (2015). [2] X. N. Wang and Y. Zhu, Medium Modification of $\gamma$-jets in High-energy Heavy-ion Collisions,'' Phys. Rev. Lett. 111, no. 6, 062301 (2013).

Speaker: TAN LUO (CCNU/LBNL)

QM2015-TanLuo.pdf

2:30 PM → 4:30 PM Open Heavy Flavors and Strangeness II

Convener: Frank Geurts (Rice University (US))

2:30 PM Charm degrees of freedom above deconfinement

The heavy quarks are one of the most versatile probes of the strongly coupled QCD medium created in the heavy ion collision experiments. However, the interactions of the heavy quarks or heavy quark bound states with the strongly coupled medium is still not well understood. One of the ways to look at such interactions is to study the behaviour of open charm hadrons in the thermalized medium. In our earlier study [1] we have shown that open charm hadrons are the relevant degrees of freedom below the QCD transition temperature. However, very little is known about the excitations of the charm degrees of freedom above the QCD transition temperature. In this work we study the nature of the excitations carrying charm in deconfined QCD medium from first principles using the lattice data on fluctuations of charm and its correlations with baryon number and strangeness. Assuming that the total charm pressure can be written as the sum of the partial pressures of charm mesons, charm baryons and charm quarks we extract the corresponding partial pressures from the lattice data. We observe that the partial meson and baryon pressures are significant till temperatures of about 200 MeV, implying that meson and baryon excitations survive well beyond the QCD transition temperature till about 200 MeV. Above that temperature quark like excitations start dominating. We also probe the relative importance of excitations carrying different quantum numbers, specifically we show that possible diquark excitations carrying a charm quantum number are not important for thermodynamics. Our studies could be important in understanding the energy loss mechanism and flow of the heavy quarks in the QGP as well as the hadronization mechanism of the open charm states. Reference: A. Bazavov, et.al., Physics Letters B 737, 210 (2014) .

Speakers: Peter Petreczky (BNL), Peter Petreczky (BNL)

qm15.pdf

2:50 PM PHENIX measurement of single electrons from charm and bottom decays at midrapidity in Au$+$Au collisions

PHENIX has measured single electrons from charm and bottom decays at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. Previous heavy-flavor electron measurements have indicated substantial modification of the momentum distribution of the parent heavy-flavor hadrons. Using the PHENIX barrel silicon-vertex tracker (VTX) to measure displaced vertices precisely, the relative contributions from charm and bottom hadrons to these electrons have been measured as a function of transverse momentum in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV. The heavier bottom quarks significantly extend our probes of the quark-gluon plasma, and the results are compared with theoretical calculations.

Speaker: Darren McGlinchey (University of Colorado)

McGlinchey_QM2015.pdf

3:10 PM Nuclear Modification Factors of D Meson Production in Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV

The mass of charm quarks is larger than the scales of the medium created in heavy­-ion collisions at RHIC energies (m_c >> Λ_QCD, T, m_u,d,s ). Therefore, charm production is mainly feasible in the primordial nucleon-­nucleon collisions and experience all the subsequent stages of the medium evolution. The modification of charm quark production in heavy -ion collisions and signatures of their interactions with the created medium are imprinted on the final kinematics of charmed mesons which can be studied experimentally using Nuclear Modification Factors (NMFs). Recent measurement of D⁰ NMFs has shown rich enhancement and suppression structures in different transverse-momentum regions that shed light on the intricate interplay of Cold Nuclear Matter effects, collectivity with the bulk matter, hadronization mechanisms and energy loss of charm quarks in heavy-­ion collisions. Higher precision measurements of NMFs are instrumental for accurately delineating the roles of these different mechanisms, their system size and kinematics dependencies, and can ultimately help in extracting medium parameters. To this end, we will discuss the topological reconstruction of D mesons via their hadronic decay channels (D⁰ → Kπ, D^+/-→ K π π and D^*+/- →D⁰ π → K π π) utilizing STAR’s recently installed Heavy Flavor Tracker for secondary vertex identification. We will also discuss transverse-momentum and centrality dependence of D meson productions and NMFs and compare them with published data from RHIC and the LHC experiments as well as with model calculations for heavy quark production and energy loss in heavy -ion collisions.

Speaker: Guannan Xie (LBNL/USTC)

GuannanX_DMesonQM15_V0.11.pdf

3:30 PM Measurements of heavy-flavour nuclear modification factor and elliptic flow in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV with ALICE

Heavy quarks, i.e. charm and beauty, are sensitive probes of the medium produced in high-energy heavy-ion collisions. They are produced in the early stage of the collisions and are expected to experience the whole history of the collision evolution interacting with the medium constituents via both elastic and inelastic processes. The 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. $v_{2}$ is the second Fourier coefficient of the azimuthal distribution of particle momenta in the transverse plane with respect to the reaction plane. At low $p_{\rm{T}}$ it is sensitive to 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. The ALICE collaboration has measured the production and elliptic flow 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. Recent results will be discussed, and model calculations including the interaction of heavy quarks with the hot, dense, and deconfined medium will be confronted with the data.

Speaker: Andrea Dubla (Nikhef National institute for subatomic physics (NL))

HF_PbPb_QM_ADubla.pdf

3:50 PM Beauty production in heavy ion collisions 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 fully reconstructed B mesons in pPb collisions at 5.02 TeV as a function of transverse momentum and rapidity. The measurement of nuclear modification factor of $J/\psi$ produced in B meson decays as a function of transverse momentum and centrality will also discussed. The measurement of fully reconstructed B meson in PbPb collisions at 2.76 TeV and prospective for the Run II analysis at 5 TeV will be presented.

Speaker: Jian Sun (Purdue University (US))

HFproduction_QM2015_v5.pdf

4:10 PM event by event correlations between light and heavy mesons

Heavy mesons are one of the few probes which allow for studying the properties of a plasma of quarks and gluons (QGP) created in ultra-relativistic heavy ion collisions. To do this we have to follow the heavy quarks from their production point through the QGP up to the final rescattering of heavy mesons with hadrons after the hadronization. The interaction of heavy quarks in the QPG is calculated in pQCD with a running coupling constant and including elastic as well as radiative collisions (arXiv 1307.5270). Due to event by event fluctuations the interaction of heavy mesons in the hadronic phase depends on the light quarks/mesons which are produced simultaneously with the heavy quarks during the initial phase of the heavy ion reaction. Therefore the observables of the heavy and light hadrons are correlated and both have to be studied simultaneously. Combining the event generator EPOS with our Heavy Quark approach we can for the first time present event-by-event results simultaneously for the light and heavy meson sector and overcome by this uncertainties of the heavy quark observables due to the ambiguities in the plasma expansion (arXiv:1102.1114). We will present detailed studies for pA in which also a (small) plasma is created to explore cold nuclear matter effects and an analysis of AA collisions, simultaneously in the light and heavy mesons sector to show which information about the elementary interaction between heavy quarks and partons is contained in the presently available data.

Speaker: joerg aichelin (Subatech/CNRS)

aichelin.pdf

2:30 PM → 4:30 PM Initial State Physics and Approach to Equilibrium I

Convener: Sangyong Jeon (McGill University (CA))

2:30 PM Re-weighting at the LHC: the p-Pb data impact

One of the goals of the proton-lead run at the LHC is to produce a benchmark for heavy-ion collisions. Preliminary analyzes hint that nPDFs fail to give a proper description for certain observables. Here we present a full study of the compatibility between current sets of initial state nuclear distributions and data from the LHC p-Pb run. By means of reweighting techniques [1,2] we give a quantitative estimate of the modification of nPDFs due to the novel proton-lead data, and also determine wether or not performing a new extraction of nPDFs is mandatory at this point. [1] H. Paukkunen and P. Zurita. JHEP 1412 (2014) 100. [2] N. Armesto, J. Rojo, C.A. Salgado and P. Zurita. JHEP 1311 (2013) 015.

Speaker: Maria Zurita (Universidade de Santiago de Compostela)

QM2015-Zurita.pdf

2:50 PM Charged-Particle Multiplicity Distributions over Wide Pseudorapidity Range in Proton-Proton Collisions with ALICE

The distribution of charged particles produced in high energy pp collisions, $P(N_{ch})$, as a function of $N_{ch}$, is sensitive to the number of collisions between quarks and gluons contained in the colliding systems and to the mechanisms underlying particle production. In particular, it is a good probe for the saturation density of gluons in the colliding hadrons. For the first time, the multiplicity distributions for pp collisions are measured over a wide kinematic range at the LHC (pseudorapidity coverage of $-3.4<\eta<+5.1$). The $P(N_{ch})$ are obtained at LHC Run 1 energies: from $\sqrt{s}=$0.9 to 8 TeV, and at the highest available energy $\sqrt{s}=$13 TeV from Run 2. The distributions are measured using the Forward Multiplicity Detector (FMD) and the Silicon Pixel Detector (SPD) of ALICE at LHC. The results are compared, where possible, with the results of other LHC experiments and with Monte Carlo simulations. Moreover, data are compared using the Koba--Nielsen--Olesen (KNO) model, where it appears that the scaling predicted by this model is broken at energies from 0.9 TeV.

Speaker: Valentina Zaccolo (University of Copenhagen (DK))

QuarkMatter2015_Zaccolo.pdf

3:10 PM Centrality and pseudorapidity dependence of transverse energy flow in pPb collisions at 5.02 TeV with CMS

The CMS Collaboration has measured the pseudorapidity and centrality dependence $dE{T}/d\eta$ for 5.02 TeV pPb collisions over 10 units of pseudo-rapidity. This was carried out in a systematic way by measuring centrality using different experimental definitions. As the centrality increases the mean pseudorapidity moves backwards and the $1/N dE_{T}/d\eta$ distribution widens. For the most central pPb collisions the maximum $1/N dE_{T}/d\eta$ reaches 25 GeV. The rate of change of dEt/deta with eta and centrality is characterized by the ratio $S_{pc} (eta, centrality) = E_{T} (\eta, centrality)/E_{T}(\eta, centrality=0-10\%)$. This ratio depends very strongly upon the definition of centrality and shows strong auto-correlations if a particular eta region is used to define centrality. For the most central events there is a large overlap in the event classes selected by different centrality measurements, but for peripheral events different centrality measures select quite different. This is quite different to the situation in PbPb and suggests that event-by-event fluctuations in the pseudorapidity distribution of particles are much stronger in pPb than in PbPb.

Speaker: Michael Murray (University of Kansas (US))

MMurrayTest.pdf

3:30 PM Initial state from holography

Through holography we can collide arbitrary lumps of energy in strongly coupled gauge theories, where we assume transverse gradients are small in the very first moments of the collision. This can be applied to off-central collisions and subsequently evolved using the MUSIC 3+1D hydrodynamic code. This allows us to compare to experimental observables, where we focus on the multiplicity and directed flow as a function of rapidity. These show qualitative agreement with data, although the multiplicity profile at our very strong coupling calculation is significantly narrower than the data, both at RHIC and especially at LHC energies. Lastly, we will present new results, using the holographic model to study initial anisotropy and entropy when including event-by-event fluctuations, but without hydrodynamics. References: arxiv:1507.xxxx, WS and B. Schenke, Directed flow in holographic heavy ion collisions

Speaker: Wilke van der Schee (MIT)

Talk_QM2015.pptx

3:50 PM Initial state azimuthal anisotropies in small collision systems

Recent experimental results have revealed a surprisingly rich structure of multiparticle azimuthal correlations in high energy proton-nucleus collisions. Final state collective effects can be responsible for many of the observed effects, but it has recently been shown that a part of these correlations are present already in the wavefunctions of the colliding particles. A domain structure at length scales of the inverse saturation scale, present in the classical color field of a high energy nucleus, naturally leads to such multiparticle correlations. This talk discusses recent work on azimuthal anisotropy coefficients originating from the initial stage color fields. In particular, we describe a recent calculation [1] of the momentum space 2-particle cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. These would correspond to the flow coefficients in very forward proton-nucleus scattering. This calculation finds significant differences between Wilson lines from the MV model and from JIMWLK evolution. The talk also discusses the relation [2] of this calculation to earlier work on the ridge correlation obtained in the "glasma graph" approximation [3], and to the "field domain model" [4] where the correlations would originate from a novel nongaussian fluctuation structure in the nuclear color field. [1] T. Lappi, Phys. Lett. B744 (2015) 315-319 [2] T. Lappi, S. Schlichting, B. Schenke and R. Venugopalan, in preparation [3] K. Dusling and R. Venugopalan, Phys. Rev. Lett. 108 (2012) 262001, Phys. Rev. D87 (2013) 054014, Phys. Rev. D87 (2013) 051502, Phys. Rev. D87 (2013) 094034 [4] A. Dumitru and A. V. Giannini, Nucl. Phys. A933 (2014) 212, A. Dumitru, L. McLerran and V. Skokov, Phys. Lett. B743 (2015) 134, A. Dumitru and V. Skokov, Phys.Rev. D91 (2015) 7, 074006

Speaker: Tuomas Lappi (University of Jyvaskyla)

qm15.pdf

4:10 PM Azimuthal Harmonics at RHIC and LHC energies: Competition between Initial State Bremsstrahlung and Final State Hydrodynamics

Recent azimuthal correlation data from d+Au and Au+Au collisions at RHIC energies and cumulant azimuthal harmonics in p+Pb and PbPb at LHC energies display very similar size and characteristics challenging the uniqueness of local equilibrium hydrodynamical interpretation of these data. We show that in p+A collisions the azimuthal harmonics arising from initial-state non-abelian interference effects associated with multiple projectile and target beam jets are remarkably similar to the measured data in experiments and predictions from final state perfect fluid models. The corresponding GLVB model description for pA collisions [1] and its numerical interpretation and inclusion will be shortly summarized and discussed. [1] M. Gyulassy, P. Levai, I. Vitev, T.S. Biro, Phys. Rev. D90 (2014) 054025.

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

LevaiP_QM2015_0928_Kobe.pdf

4:30 PM → 5:00 PM Coffee Break

5:00 PM → 7:00 PM Correlations and Fluctuations II

Convener: Joachim Stroth (Johann-Wolfgang-Goethe Univ. (DE))

5:00 PM NA61/SHINE results on fluctuations and correlations in p+p and Be+Be interactions at CERN SPS energies

The aim of the NA61/SHINE strong interaction programme is to explore the phase diagram of strongly interacting matter. The main physics goals are the study of the onset of deconfinement and the search for the critical point of strongly interacting matter. These goals are pursued by performing an beam momentum (13A - 158A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La) scan. This contribution presents results on transverse momentum and multiplicity fluctuations from the Be+Be and p+p energy scan. Also, results on two-particle correlations in pseudorapidity and azimuthal angle obtained in p+p interactions will be shown. The influence of conservation laws and resonance decays on multiplicity and chemical fluctuations of identified particles in p+p interactions will be discussed. Obtained results will be compared with other experiments and with model predictions.

Speaker: Maja Katarzyna Mackowiak-Pawlowska (Warsaw University of Technology (PL))

qm2015_mmp.pdf

5:20 PM Indications for a Critical End Point in the Phase Diagram for Hot and Dense Nuclear Matter

Excitation functions for the Gaussian emission source radii difference ($R_{out}^2-R_{side}^2$) obtained from two-pion interferometry measurements in Au+Au ($\sqrt{s_{NN}}=7.7–200$ GeV) and Pb+Pb ($\sqrt{s_{NN}}=2.76$ TeV) collisions are studied for a broad range of collision centralities. The observed nonmonotonic excitation functions validate the finite-size and finite-time scaling patterns expected for the deconfinement phase transition and the critical end point (CEP), in the temperature versus baryon chemical potential ($T,\mu_B$) plane of the nuclear matter phase diagram [1]. A Dynamic finite-size scaling (DFSS) analysis of these data suggests a second order phase transition with the estimates $T^{cep}\sim 165$  MeV and $\mu_B^{cep}\sim 95$ MeV for the location of the critical end point. The critical exponents ($\nu \approx 0.66$ and $\gamma \approx 1.2$) extracted via the same DFSS analysis place this CEP in the 3D Ising model universality class. [1] Roy. A Lacey, Phys.Rev.Lett. 114, 142301, (2015)

Speaker: Roy Lacey (Stony Brook University)

Lacey_QM2015-c.pptx

5:40 PM Systematics of higher order net-baryon number fluctuations at small values of the baryon chemical potential: A comparison of lattice QCD and beam energy scan results

Fluctuations of and correlations among conserved charges of strong interactions have long been considered sensitive observables for the exploration of the structure of the phase diagram of QCD. Cumulants of conserved charge fluctuations are the most promising experimental observables in the search for a critical point in the phase diagram of QCD performed in the beam energy scan (BES) at RHIC. The published data on cumulants of net-proton number fluctuations and, in particular, the still preliminary data set on net-proton fluctuations which covers a larger transverse momentum range show obvious deviations from the thermodynamics of a hadron resonance gas (HRG). This naturally raises the question whether ratios of cumulants of net-proton number fluctuations, and the relation between them and net electric charge cumulants measured by STAR and PHENIX can be understood in terms of equilibrium thermodynamics obtained from lattice QCD calculations. We present results for cumulants of net-baryon number and net electric charge fluctuations calculated in a next-to-leading order (NLO) Taylor series in the baryon chemical potential ($\mu_B$). We discuss the resulting pattern of ratios of cumulants, e.g. $\kappa_B\sigma_B^2\equiv \chi_4^B/\chi_2^B$ and $S_B\sigma_B^3/M_B\equiv \chi_3^B/\chi_1^B$. We note that both quantities are identical at $\mu_B=0$ and that the curvature of the latter is about three times larger than the former. Comparing this generic structure with STAR results on net-proton number fluctuations we conclude that current BES results at energies $\sqrt{s} \ge 19.6$~GeV are compatible with QCD thermodynamics and can be understood in a NLO Taylor expansion. We also discuss changes of freeze-out parameters that arise from the new, preliminary STAR data on net-proton fluctuations compared to the published data and the recent PHENIX data on electric charge fluctuations.

qm2015.pdf

6:00 PM Modeling chiral criticality and its consequences for heavy ion collisions

Considering effective models constructed to be in the same universality class as QCD, we discuss the role of critical fluctuations in the vicinity of the chiral transition. In recent lattice calculations [Ejiri et al., Phys. Rev. D 80 (2009) 094505 ] QCD with physical quark masses is found to be in the scaling regime of the O(4) universality class. We examine the O(4) scaling in the context of effective models at small net baryon density and discuss differences and similarities with lattice QCD results and their consequences. Moreover, we explore the critical fluctuations near the chiral critical endpoint (CEP), which belongs to the Z(2) universality class, in a chiral effective model and discuss possible signals of the CEP, recently explored in nuclear collision experiments [Adamczyk et al., Phys. Rev. Lett. 113 (2014) 092301]. Particular attention is attributed to the dependence of such signals on the location of the phase boundary and the CEP relative to the hypothetical freeze out conditions in nuclear collisions.

Speaker: Gabor Almasi (GSI)

QM_Almasi.pdf

6:20 PM Correlated fluctuations near the QCD critical point

Recently, STAR beam energy scan (BES) measured the multiplicity distributions of net protons with the maximum transverse momentum extended from 0.8 GeV to 2 GeV. The related higher cumulants (moments) present large deviations from the poisson baselines, showing the potential of discovery the QCD critical point in experiment. In this talk, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the classical particles with the correlated fluctuating sigma field [2]. For an infinite and stationary medium, such freeze-out scheme can reproduce the standard Staphanov formulas for cumulants presented in Ref[3]. Within this framework, we calculate the correlated fluctuations of net protons emitted from the hydrodynamic freeze-out surface at various collision energies. A comparison with recent STAR BES data shows that our model could reproduce kurtosis (and C4) through tuning the related parameters. However, the critical fluctuations in our model (also in the Stephanov formula) always give positive contributions to the cumulants C2 and C3, which over-predicts the data with poisson expectations served as the thermal fluctuation baselines[2]. In order to qualitatively /quantitatively describe these cumulants data, the effects from dynamical evolution and the deviations from poisson thermal fluctuations should be investigated in the near future. [1] X. Luo PoS CPOD2014, 019 (2014) [2] Lijia Jiang, Pengfei Li, Huichao Song, in preparation [3] M.Stephanov Phys. Rev. Lett. 102, 032301 (2009)

Speaker: Prof. Huichao Song (Peking University)

2015-09-QM2-HuichaoSong.pdf

6:40 PM Heavy-light flavor correlations and the QCD phase boundary

Modifications in magnitude of fluctuations for different observables are an excellent probe of a phase transition or its remnant. In heavy-ion collision, fluctuations related to conserved charges carried by light and strange quarks play an important role to identify the QCD chiral crossover and deconfinement properties. Recent Lattice QCD simulations have revealed that the charmed mesons are deconfined together with light-flavor mesons in the temperature range where the chiral symmetry is partially restored. This result strongly suggests that the light-flavor dynamics interferes non-trivially with the heavy flavors. We discuss correlations between the light and heavy-light flavored mesons at finite temperature within a chiral effective theory implementing heavy quark symmetry. We show that the heavy quark dynamics is tied to the light flavor physics, and the thermodynamics is strongly dragged by the chiral crossover dominated by the non-strange flavors. Consequently, the fluctuations carried by the states with strangeness can be used to characterize the onset of the chiral symmetry restoration. References: [1] C. Sasaki, Phys. Rev. D 90, no. 11, 114007 (2014). [2] C. Sasaki and K. Redlich, Phys. Rev. D 91, no. 7, 074021 (2015).

Speaker: Dr Chihiro Sasaki (FIAS & Uni of Wroclaw)

qm.pdf

5:00 PM → 7:00 PM Jets and High pT Hadrons II

Convener: Francois Gelis (Institut de Physique Theorique (FR))

5:00 PM Fragmentation patterns of jets in pPb collisions in CMS

The nuclear parton distribution function and flavor composition of hard scattering processes can be accurately studied using the jet fragmentation functions. Recent measurements of the pPb nuclear modification factor ($R_{pPb}$), with diverging values for inclusive jets and charged hadrons, have raised question on jet fragmentation properties in pPb collisions. These spectra measurements are performed with pp reference at 5.02 TeV constructed by interpolation or extrapolation from different $\sqrt{s}$, and on steeply falling power-law spectra. As the jet fragmentation function is only evolving logarithmically with $\sqrt{s}$, this further underscores the importance of a direct measurement. Together with the CMS results in pPb inclusive jets and charge hadron $R_{pPb}$, we introduce the new CMS measurement of fragmentation function in pPb collisions, where within our uncertainties, jets in pPb is found to have identical fragmentation property vs. pp jets. We will further discuss the consistency and tension among the results, and their possible origins. This measurement also gives important reference for the interpretation of the fragmentation function in PbPb collisions.

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

Baty_FragmentationPatternsinpPb_QM2015_v9.pdf

5:20 PM Exploring jet sub-structure in Pb-Pb collisions at 2.76 TeV with ALICE

We explore the possible modification of the inclusive charged jet substructure due to jet quenching in Pb-Pb collisions at 2.76 TeV by measuring a set of jet shapes. The set of shapes includes the first order angularity, the pTD and the difference between the leading and subleading tracks of the jet. The shapes are measured with a constituent cutoff of 0.15 GeV and small jet resolution $R=0.2$. New techniques for background subtraction are applied and a 2D unfolding is performed to correct the shapes to particle level. We further present differential studies of jet suppression measured via full jet $R_{\rm AA}$ as function of sub-jet structure. We systematically study the jet $R_{\rm AA}$ by selecting jets with different sub-jet structure (using collinear and infrared safe observable(s) that are robust against heavy-ion background) and present comparison to a variety of jet quenching Monte Carlo models.

Speaker: Leticia Cunqueiro Mendez (CERN)

QMCunqueiroFinalv2.pdf

5:40 PM Subjet structure as a discriminating quenching probe

Jets have proven to be a powerful experimental tool to ascertain the properties of the QGP. In this work, we propose a new class of jet substructure observables which, unlike fragmentation functions, are largely insensitive to the poorly known physics of hadronization. We show that intra jet sub-jet structures provide us with a large discriminating power between different jet quenching Monte Carlo implementations. Further, this new class of observables proves instrumental to isolate with high purity samples of strongly modified jets where the competing mechanisms of energy loss can be more easily disentangled.

Speaker: Xiaoming Zhang (Lawrence Berkeley National Lab. (US))

QM2015_Subjets.pdf

6:00 PM Jet Hadronization via Recombination of Parton Showers in Vacuum and in Medium

We have developed a hadronization model for jet parton showers based on the quark recombination model. Gluons at the end of a perturbative shower evolution undergo a non-perturbative splitting into quark and antiquark pairs, then a Monte-Carlo version of instantaneous quark recombination is applied. Finally remnant quarks (those which have not found a recombination partner) are connected by color strings and subjected to Lund string fragmentation. When applied to parton showers from the PYTHIA Monte Carlo generator, the final hadron spectra from our calculation compare quite well to PYTHIA jets that have been hadronized with the default Lund string fragmentation. This hadronization model readily generalizes to jet showers emerging from a quark gluon plasma by allowing recombination of shower partons with thermal partons, sampled from fluid dynamics or blast wave models. We find that the recombination of shower and thermal partons leads to a significant enhancement of intermediate transverse momentum pions and protons at both RHIC and LHC. Our results thus suggest that medium modification of jet fragmentation provides a plausible explanation for the enhanced production of intermediate transverse momentum hadrons and the changed hadron chemistry observed in experiments. A computer code based on this vacuum and medium hadronization model has been developed within the JET collaboration and can be combined with existing jet shower Monte Carlo codes.

Speaker: Rainer Fries (Texas A&M University)

QM_2015_Fries.pptx

6:20 PM Jet-induced medium excitation in heavy-ion collisions

We use a Linear Boltzmann Transport model (LBT model) coupled to (3+1)D ideal hydrodynamic evolution in real time with fluctuating initial conditions simulate both the transport of jet shower partons and jet-induced medium excitation. In this coupled approach, propagation of energetic shower partons are treated in the Linear Boltzmann transport (LBT) model with the 3+1D hydrodynamic model providing the evolving bulk medium. Soft partons from both elastic and inelastic processes from the LBT are fed back into the medium as a source term in the 3+1D hydrodynamic. Such source terms in the hydrodynamic will induce medium excitation. With this coupled approach we investigate hadrons spectrum in both low and high transverse momentum region and in particular in the intermediate pt region where hydro and jet contributions intersect. We will also study hadron-jet and gamma-hadron correlation to study the effect of jet-induced medium excitations.

Speaker: Mr Wei Chen (CCNU)

output-quicktime.mp4

QM_weichen.pdf

6:40 PM Consequences (and a possible explanation) of the $R_{pA}^{\rm jet}$ - $R_{pA}^{\rm hadron}$ puzzle

The experimental finding that in pA collisions at the LHC, $R_{pA}^{\rm jet}$ is consistent with unity at high transverse energies, while $R_{pA}^{\rm hadron}$ exceeds unity above $p_T \sim 30$ GeV poses a fundamental problem for our understanding of high-$p_T$ processes in nuclear collisions. It can neither be accounted for in a collinear factorized formalism with process-independent fragmentation functions, nor can it be understood as a final state modification of the final state parton shower (on which standard jet quenching models in nucleus-nucleus collisions are based). We argue that these findings, point to a process-dependent element in the high-$p_T$ fragmentation mechanism. We note that the color recombination mechanisms implemented in general purpose event generators like SHERPA provide for such a process-dependent mechanism, since they imply that single inclusive hadron production depends not only on the factorized hard partonic interaction, but also on the density of the underlying event within which this hard process color recombines during hadronization. We demonstrate both on the level of qualitative arguments and with Monte Carlo simulations that by simply accounting for the factor 3 higher underlying event activity in pA collisions as compared to pp collisions, this mechanism can account for the observed nuclear modification factors of jet and hadron spectra in pA collisions. We emphasize that if the proposed mechanism is confirmed, it has interesting consequences for the understanding of high-pT hadron spectra in proton-proton collisions, since it allows one to quantify the size of a process-dependent correction to the standard collinearly factorized framework.

Speaker: Urs Wiedemann (CERN)

QM15UrsAchimWiedemann.pdf

QM15UrsAchimWiedemann.ppt

QM15UrsAchimWiedemann.ppt

5:00 PM → 7:00 PM QGP in Small Systems I

Convener: Jiangyong Jia (State University of New York (US))

5:00 PM Direct photon production and jet quenching in small systems

Signatures usually associated with hydrodynamic behavior have been recently observed in high and intermediary multiplicity proton-nucleus (pA) collisions at the LHC. Even though these signals suggest the creation of a strongly coupled quark-gluon plasma (QGP) in such collisions, they do not represent concrete proof. In order to better address this problem, other signals must be investigated. In this work we calculate the thermal photon radiation produced by a small and rapidly expanding QGP droplet [1] and evaluate how much energy jets can loose when penetrating through such a small system. We find that a significant amount of thermal radiation is produced in proton-nucleus collisions, with thermal photons accounting for ~50% of the direct photons produced in high multiplicity pA collisions at low $p_T$. Furthermore, we show that despite the small system size, jets still loose a significant fraction of their initial energy, leading to a charged hadron Raa of 0.7--0.8 at a transverse momentum of ~10 GeV. If these two signatures can be accessed by the experiments, they will serve as additional evidence that a strongly coupled QGP is being produced in proton-nucleus collisions at the LHC. To complete the analysis, we study direct photon production and jet quenching in other small systems, such as d-Au and He-Au collisions at RHIC energies. [1] C. Shen, J.-F. Paquet, G. S. Denicol, S. Jeon and C. Gale, arXiv:1504.07989 [nucl-th].

Speaker: Prof. Charles Gale (McGill University)

Gale_QM_2015.pdf

5:20 PM Flow in small systems from parton scatterings

We show that the incoherent elastic scattering of partons, as present in a multi-phase transport model (AMPT), with a modest parton-parton cross-section of $\sigma$=1.5-3 mb, naturally explains the long-range two-particle azimuthal correlations as observed in p+p and p+Pb collisions for all measured $N_{track}$ and $p_T$ bins by the LHC-CMS experiment [1]. We calculate the elliptic, $v_2$, and triangular, $v_3$, Fourier coefficients of the two-particle azimuthal correlation function in p+Pb and peripheral Pb+Pb collisions. Our results for $v_3$ are in a good agreement with the CMS data. The $v_2$ coefficient is very well described in p+Pb collisions and is underestimated for higher $p_T$ in Pb+Pb collisions. The characteristic mass ordering of $v_2$ in p+Pb is also reproduced whereas for $v_3$ such ordering is not observed [2]. An escape mechanism has been proposed recently to explain these successful model results [3]. We investigate this issue in detail and show that collisions between active partons are directly responsible for generating the final $v_n$. References: 1. Guo-Liang Ma and Adam Bzdak, Phys. Lett. B 739, 209 (2014) [arXiv:1404.4129]. 2. Adam Bzdak and Guo-Liang Ma, Phys. Rev. Lett. 113, 252301 (2014) [arXiv:1406.2804]. 3. Liang He, Terrence Edmonds, Zi-Wei Lin, Feng Liu, Denes Molnar, Fuqiang Wang, arXiv:1502.05572.

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

QM2015_MaGuoliang.pdf

5:40 PM Effects produced by multi-parton interactions and color reconnection in small systems

Multi-parton interactions (MPI) and color reconnection (CR) have raised special interest due to the fact that they can produce QGP-like effects in small systems, specifically, flow-like patterns. Now we will show that the same mechanisms produce an explicit dependence of the $p_{\rm T}$ spectra with the number of constituent quarks. In addition, a Cronin-like peak, at intermediate transverse momentum (2 $< p_{\rm T} <$ 10 GeV/$c$), and a sort of binary scaling, at higher $p_{\rm T}$, are also observed in events with large number of MPI in pp collisions. While those effects have been revealed in pA collisions at RHIC and at LHC. In pp collisions, the last two effects have not been reported. This suggests that if MPI and CR are the mechanisms which originate the observed effects, then, the conditions for jet quenching would not be satisfied in small systems. In addition, we will discuss the experimental challenges to select on MPI. Specifically, the limitations and the biases of the event multiplicity, when, it is calculated in certain kinematic regions. We will show that such a selection can be improved using new approaches based on event shapes. Among the findings we will report that the multiplicity selection bias may affect the average \pt at high multiplicity, producing the so-called second rise of $\langle p_{\rm T} \rangle$ as reported by the ALICE Collaboration. Also, it will be argued that the average expansion velocity extracted from the analysis of the $p_{\rm T}$ spectra can be increased by the same kind of bias. Results for pp collisions at $\sqrt{s}$ = 7 and 13 TeV, and comparisons with the available experimental data will be presented.

Speaker: Guy Paic (Universidad Nacional Autonoma (MX))

KOBEF.pptx

6:00 PM Differential multi-particle correlation measurements for pPb collisions at CMS

Previous CMS measurements have demonstrated the collective nature of multiparticle correlations in high-multiplicity pPb collisions at the LHC. This collectivity is consistent with a hydrodynamic flow origin. However, it can also be interpreted in terms of initial state effects arising from gluon saturation. The pseudorapidity dependence of the azimuthal Fourier coefficients ($v_n$) is expected to be sensitive to the underlying mechanism with, in the hydrodynamic picture, the longer lifetime of the fireball on the Pb-going side expected to lead to a larger flow signal than found on the p-going side. To investigate the detailed properties of the observed collectivity, differential $v_n$ values in transverse momentum ($p_T$) and pseudorapidity ($\eta$) are presented over the full range of the CMS tracker detector ($-2.4 < \eta < 2.4$) for pPb collisions at a nucleon-nucleon center-of mass energy of 5.02 TeV. Results based on multiparticle analyses involving four or more particles are shown. An event plane analysis is presented where the influence of recently demonstrated event-plane de-correlation is considered. Comparisons are made with peripheral PbPb collisions measured at similar mid-rapidity particle multiplicities. The results will be discussed in the context of current models of the longitudinal dependence of the multiparticle correlations.

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

QM2015.pdf

6:20 PM Light flavour results in p-Pb collisions with ALICE

Particle ratios provide insight into the hadrochemistry of the event and the mechanisms for particle production. In Pb-Pb collisions the relative multi-strange baryon yields exhibit an enhancement with respect to pp collisions, whereas the short-lived K$^{*0}$ resonance is suppressed in the most central events due to re-scattering. Measurements in p-Pb allow us to investigate the development of these effects as a function of the system size. We report comprehensive results on light-flavour hadron production measured with the ALICE detector in p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, covering a wide range of particle species which includes long-lived hadrons, resonances and multi-strange baryons. The measurements include the transverse momentum spectra and the ratios of spectra among different species, and extend over a very large transverse momentum region, from ~100 MeV/$c$ to ~20 GeV/$c$, depending on the particle species.

Speaker: Antonio Ortiz Velasquez (Universidad Nacional Autonoma (MX))

QM_2015_ALICE_aortiz_24.pdf

6:40 PM PHENIX results on collectivity in $^3$He$+$Au collisions

Collisions of light with heavy ions have been considered control experiments for heavy ion collisions, but measurements of long-range azimuthal correlations of light hadrons in $p(d)$+A collisions at RHIC and LHC challenge this assumption. Hydrodynamic model calculations have been successful in describing experimental results, though alternative explanations involving initial-state Glasma diagrams have not been not ruled out. Further understanding of the origin of the observed anisotropies can be achieved in $^3$He$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV, which change the shape and size of the initial reaction zone compared to $p(d)$$+$A. We present PHENIX results for $^3$He$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV. Production of neutral pions is measured in a wide transverse-momentum range and is used to study centrality dependence of the cold-nuclear-matter effects. Azimuthal correlations for rapidity separated ($\Delta\eta>3.5$) particles are measured in a wide transverse-momentum range and compared to that in $p$$+$$p$ collisions. Elliptic and triangular flow coefficients are measured for charged hadrons and their dependence on particle mass and rapidity is reported. The experimental results are compared theoretical predictions, including to models where three hot spots created by the impact of the three $^3$He nucleons on the Au nucleus expand hydrodynamically to generate triangular flow. The agreement of data with these models may indicate the formation of low-viscosity quark-gluon plasma, even in these small collision systems.

Speaker: shengli huang (PHENIX Collaboration)

Qm2015-ShengliHuang_final.pdf

Qm2015-ShengliHuang_final.pptx

5:00 PM → 7:00 PM Initial State Physics and Approach to Equilibrium II

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

5:00 PM Charge-dependent anisotropic flow in Cu+Au collisions

At the early stages of non-central heavy-ion collisions, a strong magnetic field perpendicular to the reaction plane is created. In asymmetric Cu+Au collisions, due to the difference in the number of spectators, not only the magnetic field but also a strong electric field (E-field) would be created along the reaction plane and pointing from the Au-nucleus to Cu-nucleus. The lifetime of the E-field would be short, of the order of a fraction of a fm/c. The quarks and antiquarks that have been already produced at this time would experience the Coulomb force, which result in charge separation of directed flow. Thus, the measurement of the charge-dependent directed flow in Cu+Au provides an opportunity to test different quark (charge) scenarios, e.g Pratt’s two-wave quark production, and shed light on the (anti-)quark production mechanism in heavy-ion collisions in general. Understanding the time evolution of the quark densities in heavy-ion collisions is also very important for detailed theoretical predictions of the Chiral Magnetic Effect and Chiral Magnetic Wave, which various experiments are actively searching for. The transverse-momentum dependence of the directed (dipole) flow in Cu+Au collision is also very sensitive to the system initial density gradients in the transverse plane, which can only be observed in symmetric systems as a result of density fluctuations. Measurements of the higher-harmonic flow also allows further study of hydrodynamics and the properties of QGP. In this talk, the charge-dependent directed flow in Cu+Au collisions at ¥sqrt{s_{NN}} =200 GeV measured in the STAR experiment will be presented. The results are compared with existing model predictions and implications for the dynamics of quarks production and system evolution will be discussed. Higher-harmonic flow will be also presented and compared with A+A collisions.

Speaker: Dr Takafumi Niida (Wayne State University)

QM2015_CuAu_niida_final.pdf

QM2015_CuAu_niida_revised.pdf

5:20 PM PHENIX results on flow observables in asymmetric Cu$+$Au collisions

Asymmetric collisions of large nuclei at high energy offer a unique window into many aspects of excited medium formation and evolution. Unlike symmetric collisions, an asymmetric system can have non-zero odd-order moments in its average transverse distribution of participants, and the pattern of participants from the two nuclei can have different shapes on average. In 2012, PHENIX measured particle production in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV, and we report measurements of the azimuthal anisotropies $v_1$, $v_2$, and $v_3$ (directed, elliptic, and triangular flow) for inclusive and identified charged hadrons produced at midrapidity. Implications for a variety of unique initial-state geometry effects will be discussed.

Speaker: Brennan Schaefer (Vanderbilt University)

20150928_BCS_QM2015.pdf

20150928_BCS_QM2015.ppt

5:40 PM The influence of pre-equilibrium dynamics on heavy-ion collision observables

In order to bracket the importance of the pre-equilibrium stage on relativistic heavy-ion collision observables at RHIC and LHC energies, we compare simulations in which the pre-equilibrium stage is modeled by free-streaming partons with others where it is modeled fluid dynamically. The first (second) case implements the assumption of extremely weak (strong) coupling in the initial collision stage. We introduce a switching time parameter for the duration of the weakly coupled stage; after this time the system is assumed to stay in the strongly coupled hydrodynamic stage (with a specific shear viscosity that we can vary) until freeze-out. Based on event-by-event simulations of fluctuating initial conditions, we first study observables (radial, elliptic and triangular flow) systematically as a function of the switching time from free-streaming to viscous hydrodynamics ("thermalization time"), leaving other parameters fixed. We then perform a three-dimensional simultaneous parameter fit of the switching time, specific shear viscosity and freeze-out temperature by comparing the numerical results with a set of 5 experimental observables, for four different types of initial conditions. We find that the strongest constraint on the thermalization time does not come of anisotropic flow measurements, as previously thought, but from the mean transverse momentum of hadrons with different masses (i.e. radial flow). First results from a campaign that includes bulk viscous effect and a hadronic afterburner to describe the freeze-out stage, with particular focus on the mass-ordering of the elliptic and triangular flow for protons and Lambda hyperons which is incorrectly described by VISHNU without pre-equilibrium flow, will also be shown. References: Jia Liu, Chun Shen, U. Heinz, Phys.Rev. C 91 (2015) 064906; and additional work to be published

Speaker: Ulrich Heinz (The Ohio State University)

QM2015_Heinz.pdf

6:00 PM Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. Our results are generally applicable if $\tau < 1/Q_s$. The transverse energy flow of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.

Speaker: Prof. Joseph Kapusta (University of Minnesota)

QM2015_Kapusta.pdf

6:20 PM Resumming large radiative corrections in the high-energy evolution of the Color Glass Condensate

The Color Glass Condensate effective theory is the perturbative QCD description of the initial state for proton-nucleus and nucleus-nucleus collisions at RHIC and the LHC. The BK-JIMWLK equations describing the evolution of this theory with increasing energy have recently been extended to next-to-leading order (NLO) accuracy, which should allow for direct comparisons with the phenomenology. However, some of the NLO corrections turn out to be extremely large, since amplified by (double and single) `collinear’ logarithms, i.e. logarithms of ratios of transverse momenta. As a result, the evolution at NLO becomes unstable and void of any predictive power. This difficulty points towards the existence of large radiative corrections to all orders in $\alpha_s$, which must be computed and resummed in order to restore the predictive power of the perturbative expansion. In Ref. [1], we performed such a resummation for the largest corrections — those where each power of $\alpha_s$ is accompanied by a double transverse logarithm. Subsequently, in Ref. [2], we have extended this resummation by including single transverse logarithms and running coupling corrections. This led us to a `collinearly improved’ version of BK equation, which resums the largest radiative corrections to all orders. Numerical studies of this equation show that the evolution is now stable and also considerably slowed down by the resummation. To demonstrate the usefulness of this equation as a tool for phenomenology, for have used it for fits to the HERA data for electron-proton deep inelastic scattering at high energy [2]. We have obtained excellent fits with a reduced number of free parameters and with initial conditions at low energy taken from perturbative QCD. [1] ``Resumming double logarithms in the QCD evolution of color dipoles’’, arXiv:1502.05642, Phys. Lett. B744 (2015) 293. [2] ``Collinearly-improved BK evolution meets the HERA data’’, arXiv:1507.03651

Speaker: Dr Edmond Iancu (IPhT Saclay)

Iancu_Kobe-QM2015.pdf

6:40 PM The non-trivial interplay of elastic and inelastic collisions in the thermalization of the quark-gluon plasma

To understand the approach to equilibrium of a dense system of gluons, such as those produced in the early stages of ultra-relativistic heavy ion collisions, is an outstanding challenge. We study this problem by solving the relevant kinetic equations, including the proper Bose statistics, and using simple approximations that allow for semi-analytic solutions. Both elastic processes and number changing inelastic processes are taken into account. The semi-analytical solutions that we obtain complement discussions based on parametric estimates, or purely numerical solutions, and provide new insights on the interplay of elastic and inelastic collisions during the thermalization of the quark-gluon plasma. In particular, they confirm the rapid growth at early times of soft modes, mostly due to radiation processes, which leads to the almost immediate emergence of an infrared thermal spectrum. They also illustrate the mechanisms by which the system gets rid of the large excess of gluons that it contains initially.

Speaker: Dr Jean-Paul Blaizot (CEA)

QM_2015_Blaizot.pdf

Tuesday, September 29

9:00 AM → 10:20 AM Quarkonia II

Convener: Min Jung Kweon (Inha University (KR))

9:00 AM PHENIX measurement of the collision system and multiplicity dependence of heavy quarkonia production

The system size and multiplicity dependence of heavy quarkonia production in heavy ion collisions can be used to disentangle the effects of hot and cold nuclear matter on quarkonia production. In particular, color screening and recombination, which modify the yields of charmonia in the quark gluon plasma, can be studied in large systems. We present PHENIX results on J/$\psi$ production in U$+$U collisions. The yield is compared to that in Au$+$Au collisions as a function of centrality. In peripheral to midcentral collisions the ratio scales as $N_\mathrm{coll}$, but in central collisions it scales as $N_\mathrm{coll}^2$. This is consistent with a picture where, for more central collisions, the coalescence mechanism for the production of the J/$\psi$ becomes dominant over the decrease in yield due to the increased energy density.

Speaker: Anthony Frawley (Florda State University)

QM2015_frawley_quarkonia_v3.pdf

9:20 AM Charmonium production in Pb-Pb collisions with ALICE at the LHC

Charmonia (for instance J/ψ and ψ(2S)) are mesons formed of a charm and anti-charm quark pair. In high-energy hadronic collisions such as those delivered by the LHC between 2010 and 2013, charmonium production results from the hard scattering of two gluons, which occurs very early. In heavy ion collisions, charmonia can thus probe all states of the nuclear matter formed afterward and have therefore been used extensively to study the properties of the Quark-Gluon Plasma (QGP). In this presentation we will report on published charmonium measurements performed by ALICE in Pb − Pb collisions at a center of mass energy per nucleon-nucleon collision √sNN = 2.76 TeV, at both mid (|y| < 0.8) and forward (2.5 < y < 4) rapidities. The nuclear modification factor of inclusive J/ψ will be presented as a function of the collision centrality, the J/ψ transverse momentum (pT) as well as its rapidity. The variation of the J/ψ mean transverse momentum and mean transverse momentum squared as a function of the collision centrality will also be discussed. These measurements will be compared to models that include one or several of the following mechanisms: color screening; balance between dissociation and recombination in the QGP; recombination at the QGP phase boundary; interaction with a dense comoving medium. Results on the production of the heavier and less bound ψ(2S) meson in Pb − Pb collisions at forward-rapidity will also be presented and compared to both models and measurements performed by other experiments. At mid-rapidity we will also report on ALICE unique capability to separate prompt and non-prompt J/ψ production down to low pT (≥ 1.5 GeV/c) and thus provide direct insight on the energy loss of b quarks in the QGP.

Speaker: Hugo Denis Antonio Pereira Da Costa (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))

Hugo_Pereira_QM2015.pdf

9:40 AM Upsilon production measurements in pp, p-Pb and Pb-Pb collisions with ALICE

Quarkonium, i.e. bound states of heavy quark and antiquarks ($c\bar{c}$ or $b\bar{b}$), are important observables to study the properties of nuclear matter at extreme energy-densities, where Lattice QCD calculations predict a phase transition from hadronic matter to the Quark-Gluon Plasma (QGP). In high energy heavy-ion collisions, the QGP can be studied using the suppression of bottomonium production, due to the color screening, with respect to the proton-proton results scaled by the number of binary collisions. However, this measurement can be biased by the possible presence of cold nuclear matter effects, which can be estimated using proton-nucleus collisions, where the QGP formation is not expected. ALICE measures bottomonium production at forward rapidity ($2.5\le y\le4$) down to zero transverse momentum via the dimuon decay channel. In this presentation, the nuclear modification factor of $\Upsilon$ measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV will be discussed. ALICE measurements of the bottomonium production for pp collisions will be also presented. The results will be compared to other LHC experimental measurements and to theoretical calculations.

Speaker: Indranil Das (Saha Institute of Nuclear Physics (IN))

Y_production_measurements_with_ALICE.pdf

10:00 AM In-medium quarkonium properties from a lattice QCD based effective field theory

In order to understand the experimental data on quarkonium production in heavy ion collisions at RHIC and LHC it is necessary (though not sufficient) to pinpoint the properties of heavy quarkonium in the deconfined QGP medium, including their dissolution. Studying quarkonium spectral properties at non-zero temperature, directly in lattice QCD, have proven to be difficult and detailed quantitative information on quarkonium in-medium properties is still lacking. Lattice QCD based effective theories, such as lattice NRQCD, have seen impressive success in the determination of quarkonium properties in vacuum (e.g. their masses and decay widths), with the underlying framework being applicable in principle also at finite temperature. In combination with realistic lattice QCD simulations of the QGP medium with light pion masses by the HotQCD collaboration [1] gaining reliable first-principles insight into in-medium behavior is now is in reach. Here we present our recent results on the temperature dependence of bottomonium and charmonium correlators, as well as their spectral functions in lattice NRQCD for temperatures 140 MeV < T< 400 MeV [2,3]. The spectra are reconstructed based on a novel Bayesian prescription [4], whose systematic uncertainties are thoroughly tested. We present indications for sequential melting of different quarkonium species with respect to their vacuum binding energies and discuss implications for phenomenology. [1] A. Bazavov et. al., Phys. Rev. D85 (2012) 054503; Phys. Rev. D90 (2014) 094503 [2] S. Kim, P. Petreczky, A. Rothkopf, Phys. Rev. D91 (2015) 054511 [3] S. Kim, P. Petreczky, A. Rothkopf, work in progress [4] Y. Burnier, A.R., Phys. Rev. Letters, 111 (2013) 182003

Speaker: Alexander Rothkopf (Heidelberg University)

QM2015_KOBE_ROTHKOPF.pdf

9:00 AM → 10:20 AM New Theoretical Developments II

Convener: Teiji Kunihiro (Departmento of Physics, Kyoto University (JP))

9:00 AM Strong-Coupling Effects in a Plasma of Confining Gluons

For the first time we investigate non-equilibrium dynamic properties of a plasma consisting of confining gluons resulting from Gribov quantization [1]. For this purpose we employ the infrared-improved Gribov dispersion relation of gluons in the kinetic theory setup in the relaxation time approximation and determine the exact in- and out-of-equilibrium evolution of the system. In the static case the resulting equation of state of the studied system provides a good qualitative description of the pure-glue lattice QCD data down to the vicinity of the phase transition [2,3,4], thus permitting a study of the non-equilibrium phenomena in a plasma that exhibits crucial features of the QCD phase transition. In the case of local thermal equilibrium we observe Bjorken-like cooling of the boost-invariant expanding system. Out of equilibrium, by matching to the first order viscous hydrodynamics, we calculate bulk [3] and shear [5] viscosity of the system. We find significant enhancement of the bulk to shear viscosity ratio close to the transition temperature and its universal scaling behavior, in line with the one expected in a strongly-coupled theories [5]. We interpret the onset of strongly-coupled features in the system as the possible explanation of the close to perfect fluid behavior of the quark-gluon plasma. References: 1. V. Gribov, Nucl. Phys. B 139, 1 (1978) 2. D. Zwanziger, Phys. Rev. Lett. 94, 182301 (2005) 3. W.Florkowski, R.Ryblewski, N.Su, K.Tywoniuk, arXiv:1504.03176, submitted to Phys.Rev.Lett. 4. S. Borsanyi, G. Endrodi, Z. Fodor, S. D. Katz and K. K. Szabo, JHEP 1207, 056 (2012) 5. W.Florkowski, R.Ryblewski, N.Su, K.Tywoniuk, forthcoming

Speaker: Dr Radoslaw Ryblewski (Institute of Nuclear Physics PAN)

talk.pdf

9:20 AM Matrix model of the semi-QGP with quarks

A matrix model of the semi-QGP, the region near the critical temperature, developed for the pure glue theory is applied to QCD with dynamical quarks. We add new parameters to address the spontaneous breaking of chiral symmetry breaking. The results of the model are compared to the latest results from numerical simulations on the lattice. We compute the interaction measure, the susceptibilities for the light and strange quarks, and quark number susceptibilities to eighth order. We note that a mixed susceptibility, between the Polyakov loop and the chiral order parameter, shows a mild divergence near the chiral transition.

Speaker: Robert Pisarski (Brookhaven National Lab.)

Pisarski_Quarks_QM15.pdf

9:40 AM Soft-Collinear Effective theory for hadronic and nuclear collisions: The evolution of jet quenching form RHIC to the highest LHC energies

Effective field theory (EFT) is a powerful framework based on exploiting symmetries and controlled expansions for problems with a natural separation of energy or distance scales. EFTs are particularly important in QCD and nuclear physics. An effective theory of QCD, ideally suited to jet applications, is Soft-Collinear Effective Theory (SCET). Recently, first steps were taken to extend SCET and describe jet evolution in strongly-interacting matter. In this talk I will demonstrate that the newly constructed theory, called SCETG, allows us for the first time in more than a decade to go beyond the traditional energy loss approximation in heavy ion collisions and unify the treatment of vacuum and medium-induced parton showers. It provides quantitative control over the uncertainties associated with the implementation of the in-medium modification of hadron production cross sections and allows us to accurately constrain the coupling between the jet and the medium. I will further show how SCETG is implemented to present predictions for inclusive hadron suppression in Pb+Pb collisions at the highest LHC energies of 5.1 ATeV and discuss the relative significance of cold and hot nuclear matter effects. [1] Z.B. Kang, G. Ovanesyan, R. Lashof-Regas, P. Saad, I. Vitev, Phys. Rev. Lett. 114 (2015) 9, 092002 [2] Y.-T. Chien, A. Emerman, Z. Kang, G. Ovanesyan, I. Vitev, JHEP in preparation

Speaker: Dr Ivan Vitev (LANL)

QM_Vitev_2015.pdf

10:00 AM In-medium jet evolution: interplay between broadening and decoherence effects

The description of the modifications of the coherence pattern of the parton shower when in the presence of a QGP has been actively addressed in recent studies. Among the several achievements, finite energy corrections, transverse momentum broadening due to medium interactions and interference effects between successive emissions has been extensively improved as they seem to be essential features for a correct description of heavy-ion collisions results. In this work, based on the insights of our previous work [2], we fully explore the physical interplay between broadening and decoherence, by generalising previous studies of medium-modifications of the antenna spectrum [1] - so far restricted to the case where transverse motion is neglected. The result allow us to identify two quantities controlling the decoherence of a medium modified shower that can be used as building blocks for a successful future generation of Jet quenching Monte Carlos: a generalisation of the $\Delta_{med}$ parameter of the works of [1] - that controls the interplay between the transverse scale of the hard probe and the transverse scale of the medium - and of the $\Delta_{coh}$ in [2] - that dictates the interferences between two emitters as a function of the transverse momentum broadening acquired by multiple scatterings with the medium. [1] L. Apolinário, N. Armesto, J. G. Milhano, and C. Salgado, JHEP 1502 (2015) 119 [2] Y. Mehtar-Tani, C. A. Salgado and K. Tywoniuk, Phys.Rev.Lett. 106 (2011) 122002 Y. Mehtar-Tani, C. A. Salgado and K. Tywoniuk, JHEP 1210 (2012) 197 J. Casalderrey-Solana and E. Iancu, JHEP 1108 (2011) 015

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

LApolinarioQM15.pdf

9:00 AM → 10:20 AM Collective Dynamics I

Convener: In-Kwon Yoo (Pusan National University (KR))

9:00 AM Measurement of D Meson Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV from STAR

Heavy quarks are produced through initial hard scatterings and they are affected by the hot and dense medium created in heavy-ion collisions throughout its whole evolution. Due to their heavy mass, charm quarks are expected to thermalize much more slowly than light flavor quarks. As a result, the charm quark flow is a unique tool to study the extent of thermalization of the bulk medium dominated by light quarks and gluons. At high $p_T$, D meson azimuthal anisotropy is sensitive to the path length dependence of charm quark energy loss in the medium, which offers new insights into heavy quark energy loss mechanisms - gluon radiation vs. collisional processes. In this talk, we present the STAR measurement of elliptic flow ($v_2$) of D$^0$, D$^\pm$, D$^{*\pm}$ mesons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for a wide transverse momentum range and different centrality bins. These results are obtained from the data taken in the first year of physics running of the new STAR Heavy Flavor Tracker detector, which greatly improves open heavy flavor hadron measurements by the topological reconstruction of secondary decay vertices. The D meson $v_2$ is compared with those of other particle species at the same energy, measurements at the LHC collision energy and the latest model calculations. Physics implications on charm quark flow as well as the medium transport properties are discussed.

Speaker: Michael Lomnitz (Kent State University)

QM15DMesonv2.pdf

9:20 AM Beam-Energy and Centrality Dependence of Directed Flow of $\Lambda$, $\bar\Lambda$, $\phi$, $K^0_s$, $K^\pm$, $p$, $\bar{p}$, $\pi^\pm$

The Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider aims to study the QCD phase diagram in regions where net baryon density is large, a region where a critical point may exist. Possible signatures of a softening of the QCD equation of state have been reported at BES energies, and directed flow (rapidity-odd $v_1(y)$) is one of the more striking examples in this category. This talk will focus on $v_1$, and its slope $dv_1/dy$, near midrapidity. Ten identified particle types will be presented: $\Lambda$, $\bar\Lambda$, $\phi$, $K^0_s$, $K^\pm$, $p$, $\bar{p}$, and $\pi^\pm$ produced in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV as a function of rapidity. For $\Lambda$, $K^0_s$, $K^\pm$, $p$ and $\pi^\pm$, all results are presented in the centrality bins $0-5\%$, $5-10\%$, $10-20\%$, $20-30\%$, $30-40\%$, $40-50\%$, $50-60\%$, $60-70\%$ and $70-80\%$. At intermediate centrality (10-40\%), $dv_1/dy$ shows a minimum near 14.5 GeV for several particle species while $p$ and $\Lambda$ also show a sign change. The $\phi$ meson appears to follow $\bar{p}$ at the higher BES energies, while protons, kaons and pions have a lower magnitude than $\bar{p}$ at 14.5 GeV and above. $\Lambda$ and $p$ are consistent within errors at all energies. $dv_1/dy$ shows a strong centrality dependence, especially for $p$ and $\Lambda$ at the lower beam energies. Results for net kaons and net protons will also be discussed. The UrQMD model shows a qualitatively similar trend for only a subset of the ten particle types under investigation. This comprehensive set of directed flow measurements for several identified baryons, antibaryons and mesons, spanning BES energies and all centralities, offers a powerful constraint on model calculations.

Speaker: Prashanth Shanmuganathan (Kent State University, USA)

398_Prashanth_Shanmuganathan_BES_v1.pdf

398_Prashanth_Shanmuganathan_BES_v1.pptx

9:40 AM (Anti-)deuteron production and anisotropic flow measured with ALICE at the LHC

The high abundance of (anti-)deuterons in the statistics gathered in run 1 of the LHC and the excellent performance of the ALICE setup allow for the simultaneous measurement of the elliptic flow and the deuteron production rates with a large transverse momentum ($p_{\rm T}$) reach. The (anti-) deuterons are identified using the specific energy loss in the time projection chamber and the velocity information in the time-of-flight detector. For nuclei of higher energies, the High Momentum Particle IDentification (HMPID), a ring-imaging Cherenkov detector, is also utilized. The elliptic flow of (anti-)deuterons could provide insight into the production mechanisms of particles in heavy-ion collisions. While one of the approaches to describe the elliptic flow of hadrons and light nuclei, is given by quark coalescence, the production of light nuclei is also depicted as a coalscence of nucleons, i.e. hadron coalescence. Differences should be visible for those two approaches when the elliptic flow is measured simultaneously with the $p_{\rm T}$ spectra, especially when they are scaled by the number of nucleons and quarks. The results are compared to expectations from coalescence and hydrodynamic models which aim at describing both the $p_{\rm T}$-spectra and the elliptic flow.

Speaker: Ramona Lea (Universita e INFN, Trieste (IT))

DeuteronFlow.pdf

10:00 AM Event shape engineering with the ALICE detector

Event shape engineering (ESE) is a differential technique, which involves selecting events based on their anisotropic flow, and studying other observables with respect to the magnitude of that flow [1]. These studies have been pursued by the ALICE, ATLAS, and PHENIX collaborations, and promise to open up a new paradigm in the era of high statistics heavy-ion data. We will show the latest results from the ALICE collaboration for Pb-Pb 2.76 TeV collisions. In particular, we will show new studies on event by event correlations of radial and anisotropic flow, and discuss how these studies can place extra constraints on the initial conditions. We will demonstrate how the pion, kaon, proton spectra evolve with the event-wise anisotropic flow, and use a blast wave model to determine changes in the radial flow velocity. We will also review the sensitivity of the ESE technique, by comparing results using different ALICE sub-detectors. Finally, we will discuss the feasibility of more statistically demanding ESE studies for the upcoming LHC run 2 and 3 data. [1] Ultra-relativistic nuclear collisions: Event shape engineering, J. Schukraft, A. Timmins, S. Voloshin, J. Phys. Lett. B $\bf 719$ (2013) 394–398

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

atimminsESEQMv3a.pdf

9:00 AM → 10:20 AM Open Heavy Flavors and Strangeness III

Convener: Zaida Conesa Del Valle (CNRS/IN2P3 - Universite de Paris-Sud 11 (FR))

9:00 AM PHENIX measurement of $b\bar{b}$ production in $p$$+$$p$ collisions

PHENIX has measured the $b\overline{b}$ production cross section in $p$$+$$p$ collisions at $\sqrt{s} = 500$~GeV. In the absence of displaced-vertex $b$-tagging, this is made possible by exploiting the properties of $B^{0}-\overline{B^{0}}$ oscillations. Like-sign muon pairs in the PHENIX muon arms are measured in order to extract this signal. We report the $b\overline{b}$ differential cross section in the rapidity range $1.2 < |y| < 2.2$, for dimuon masses in the range 5--10~GeV/$c^2$, and extrapolate to the total-production cross section.

Speaker: Abhisek Sen (Georgia State University)

qm15_abhisek_v4.pdf

9:20 AM Measurements of heavy-flavour production in p--Pb collisions with ALICE

The ALICE experiment's heavy-ion programme allows us to study the hot, high energy-density state of matter formed in ultrarelativistic nuclear collisions. In particular, heavy quarks (charm and beauty) serve as calibrated probes of the medium, since they are predominantly produced during the initial hard scatterings in the collision. ALICE's excellent tracking, vertexing and particle identification capabilities allow it to fully reconstruct the hadronic decays of open-charmed D mesons, as well as enabling the study of leptons stemming from charm and beauty decays at forward and mid-rapidity. Measurements in p--Pb collisions allow us to disentangle experimental observations arising due to the hot and dense medium from those occurring due to cold nuclear matter effects such as momentum broadening, initial-state energy loss, and the modification of nuclear PDFs in the Pb nucleus. In particular, it is possible to measure nuclear modification factors in p--Pb and Pb--Pb collisions in order to determine whether the observed suppression of particles at high $p_\mathrm{T}$ in central Pb--Pb collisions is a medium-induced effect. Further insight into cold nuclear matter effects can be obtained by examining the yields of D mesons as a function of charged-particle multiplicity in p--Pb collisions. Here we present the most recent results from ALICE for charm and beauty production in p--Pb collisions via heavy-flavour decay electrons at mid-rapidity, heavy-flavour decay muons at forward rapidity, and the hadronic decays of D$^0$, D$^+$, D$^{\star +}$ and D$_\mathrm{s}^+$ mesons at mid-rapidity.

Speaker: Jeremy Wilkinson (Ruprecht-Karls-Universitaet Heidelberg (DE))

aliceopencharminppb_jwilkinson_qm2015.pdf

9:40 AM Heavy-flavour correlations and multiplicity dependence in pp and p--Pb collisions with ALICE

The study of heavy-quark production (charm and beauty) in pp collisions at LHC energies allows us to test perturbative QCD calculations and provides a reference for studies in heavy-ion collisions. Measurements in p--Pb collisions help to characterize the effects due to the presence of a nucleus in the collision (cold nuclear matter effects). ALICE has provided measurements of the nuclear modification factor $R_{\rm pPb}$ in the heavy-flavour sector. More differential measurements of charm and beauty production in pp and p--Pb collisions can provide further insight on the above topics. The analysis of angular correlations between heavy-flavour particles and charged particles allows us to characterize the heavy-quark fragmentation process and is sensitive to their production mechanism. Differences between the measurements in pp and p--Pb collisions can give insight on how cold nuclear matter effects affect the heavy-quark production and hadronisation in p--Pb collisions. In the analysis of hadron-hadron correlations in p--Pb collisions, a double-ridge long-range structure was observed, possibly coming from a collective behavior of the system or gluon saturation in the initial state. This feature can be investigated for heavy quarks as well through heavy-flavour correlation studies. Moreover, the study of heavy-flavour production in pp collisions as a function of the charged-particle multiplicity is a powerful tool to investigate the interplay between hard and soft QCD processes responsible for particle production in hadronic collisions and provides information on the role of multi-parton interactions. We present ALICE measurements of azimuthal correlations between prompt D mesons and heavy-flavour decay electrons with charged hadrons in pp collisions at $\sqrt s$ = 7 TeV and p--Pb collisions at $\sqrt {s_{\rm NN}}$= 5.02 TeV. We also show the per-event yields of D mesons as a function of the charged-particle multiplicity in pp collisions at $\sqrt s$ = 7 TeV.

Speaker: Fabio Filippo Colamaria (Universita e INFN, Bari (IT))

QM2015_HF multiplicity and correlations_FColamaria.pdf

10:00 AM Medium-effects on heavy-flavour production in large and small systems

Predictions obtained with the up-to-date version of our POWLANG transport code for heavy-flavour production in high-energy nuclear (A-A and now also p-A) collisions will be presented. To the usual Langevin evolution in the plasma we added a new modeling of the hadronization stage including the recombination with thermal partons from the medium at the decoupling hypersurface, to form colour-singlet strings eventually fragmented according to the Lund model implemented in PYTHIA. The additional radial and elliptic flow inherited by the heavy-flavour hadrons from the light quarks will affect the final observables, providing a better agreement with the experimental data for RAA and v2. We will show how, with our setup, it is also possible to study more differential observables like various kind of azimuthal correlations: D-h, e-h -- for which experimental data start getting available -- but also D-Dbar or e+-e-, not yet experimentally accessible but allowing in principle a more direct information on the decorrelation occurred at the partonic level. If the interaction with the medium tends to partially wash-out the initial Q-Qbar angular correlation, the elliptic flow acquired in the medium and at hadronization will tend to introduce a common correlation of all the heavy-flavour hadrons with the reaction plane, which will also contribute to the experimental signal. Finally we will display the first results of our ongoing study on heavy-flavour observables in small systems, like the ones produced in p-Pb or d-Au collisions, trying to check whether the presence of a hot medium suggested by observables in the light sector (e.g. double ridge, elliptic flow...) can leave its fingerprints also in heavy-flavour signals.

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

QMberaudo.pdf

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:30 PM Jets and High pT Hadrons III

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

10:50 AM A Comprehensive Analysis of Jet Quenching via a Hybrid Strong/Weak Coupling Model for Jet-Medium Interactions

Within a hybrid strong/weak coupling model for jets in strongly coupled plasma, we explore jet modifications in ultra-relativistic heavy ion collisions. Our approach merges the perturbative dynamics of hard jet evolution with the strongly coupled dynamics which dominates the soft exchanges between the fast partons in the jet shower and the strongly coupled plasma itself. We implement this approach in a Monte Carlo, which supplements the DGLAP shower with the energy loss dynamics as dictated by holographic computations, up to a single free parameter that we fit to data. We confront our model with available single jet, dijet and photon-jet data in Pb-Pb collisons at $\sqrt{s}=2.76$~ATeV and we obtain a satisfactory description after fitting one single parameter. We use our model to predict a broad range of dijet, photon-jet and Z-jet observables for the upcoming LHC Run II, at $\sqrt{s}=5.02$~ATeV. We then augment the model by incorporating the transverse momentum picked up by each parton in the shower as it propagates through the medium, at the expense of adding a second free parameter. We use this model to discuss the influence of the transverse broadening of the partons in a jet on intra-jet observables. In addition, we explore the sensitivity of such observables to the back-reaction of the plasma to the passage of the jet. Finally, we comment on the sensitivity of the different observables we have analyzed to the microscopic dynamics of the jet-plasma interaction.

Speaker: Mr Daniel Pablos (Universitat de Barcelona)

PablosQM15.pdf

11:10 AM Consistency of Perfect Fluidity and Jet Quenching in semi-Quark-Gluon Monopole Plasmas

We utilize a new framework, CUJET3.0, to deduce the energy and temperature dependence of the jet quenching parameter, $\hat{q}(E>10\;{\rm GeV},T)$, from a combined analysis of available data on the nuclear modification factor and azimuthal asymmetry of high $p_T$ light hadrons and open heavy flavors in high-energy A+A collisions at RHIC and LHC. Extending a previous perturbative QCD based jet energy loss model (known as CUJET2.0) with (2+1)D viscous hydrodynamic backgrounds, this new framework includes three novel features of nonperturbative physics origin: (1) the Polyakov loop suppression of color-electric scatterings and (2) the enhancement of the jet scattering due to emergent chromomagnetic monopoles near $T_c$ and (3) thermodynamic properties constrained by lattice QCD data. CUJET3.0 reduces to CUJET2.0 at high temperatures $T > 400$ MeV, but greatly enhances $\hat{q}$ near the QCD deconfinement transition temperature. This enhancement accounts well for the observed elliptic harmonics of jets with $p_T>10$ GeV. Extrapolating our data-constrained $\hat{q}$ down to thermal energy scales, $E \sim 2$ GeV, we find for the first time a remarkable consistency between the high energy jet quenching and bulk perfect fluidity with $\eta/s\sim T^3/\hat{q} \sim 0.1$ near $T_c$. References [1] Jiechen Xu, Jinfeng Liao, Miklos Gyulassy, arXiv:1411.3673 [hep-ph]. [2] Jiechen Xu, Alessandro Buzzatti, Miklos Gyulassy, JHEP 1408, 063 (2014).

Speaker: Jiechen Xu (Columbia University)

QM15-JiechenXu.pdf

11:30 AM Direct-photon+hadron correlations to study parton energy loss with the STAR experiment

Photons are valuable probes of the QCD plasma due to their lack of color and electric charge. Direct photons ($\gamma_{dir}$), those produced during the collision rather than from decays of hadrons, are not affected by the medium.The study of direct-photon-triggered away-side jets can give information about the energy loss of the away-side parton while traversing through the medium. On the other hand, comparison between the suppression of $\gamma_{dir}$- and $\pi^{0}$- triggered away-side hadron yields can give information about the path-length and color-factor dependence of parton energy loss. We report new results of $\gamma_{dir}$+hadron and $\pi^{0}$+hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment from years 2011 and 2009 of data taking, respectively. The charged-hadron per-trigger yields at mid-rapidity $(|\eta| < 1)$ and for transverse momenta $p_{T}^{assoc} > 1.2$ GeV/c associated with $\gamma_{dir}$ and $\pi^{0}$ (for triggers $|\eta| < $0.9, 12 $< p_{T}^{trig} <$ 20 GeV/c) in central Au+Au collisions are compared with p+p collisions. With this new low $p_{T}^{assoc}$ cut, we see evidence for the recovery of the lost energy in the low-momentum range for the constituents of the jet.The $z_{T}$ ($= \frac{p_{T}^{assoc}}{p_{T}^{trig}}$) dependence, now extending down to $z_{T}$=0.1, of the suppression of the away-side associated yields is presented. The dependence of the suppression on both $p_{T}^{assoc}$ and $p_{T}^{trig}$ is also discussed. Finally, these results are compared with various model predictions.

Speaker: Dr Nihar Sahoo (Texas A & M University)

QM15_Nihar_tamu_STAR.pdf

11:50 AM PHENIX results on jet correlations via high-$p_T$ hadrons and photons

Suppression of high $p_{T}$ hadrons in heavy ion collisions is a well-known phenomenon, understood to be a result of in-medium energy loss of partons. To explore more precisely the underlying energy loss mechanism, PHENIX has measured many complementary observables. Fractional energy loss of single hadrons vs the number of participants in Au$+$Au and Cu$+$Cu collisions reveal scaling laws which can constrain models. Back-to-back correlations between direct photons and hadrons provide access to the initial parton energy prior to in-medium interactions. Two-particle correlations with an azimuthal angle selection of the trigger particle with respect to the reaction plane can control for the parton path length inside the medium. Comparing near-side to away-side correlations in $d$$+$Au collisions to those in $p$$+$$p$ collisions provides a precise measurement of possible cold nuclear matter effects or other phenomena not yet accounted for. Recent results from PHENIX on high-$p_{T}$ particle correlations will be presented.

Speaker: Ali Hanks

AHanks_QM2015_final.pdf

12:10 PM Azimuthal anisotropy of charged jet production in $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV Pb--Pb collisions with ALICE

Jets in heavy-ion collisions are used to probe the QGP, as medium-induced parton energy loss from elastic and radiative interactions between partons and the QCD medium will lead to a modification of the measured jet spectrum. The dependence of the energy loss on the in-medium path length provides deeper insight into the energy loss mechanisms and can be studied by measuring jet production relative to the event plane orientation. This contribution will show results of measurements of $R=0.2$ charged jet production in central and peripheral $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV Pb--Pb collisions with respect to the second order event plane, quantified as $v_2^{\mathrm{jet}}$. Jet finding is performed with the anti-$k_{\mathrm{T}}$ algorithm using charged tracks from the ALICE tracking system. The contribution of hydrodynamic flow to the underlying event energy is taken into account event-by-event; remaining fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations separately. Significant non-zero $v_2^{\mathrm{jet}}$ is observed for peripheral collsions for 20 $<$ $p_{\mathrm{T}}$ $<$ 100 GeV/$c$; in central collisions this effect is less pronounced. Comparisons to $v_2$ of charged particles at high momenta and azimuthally dependent jet production studies of ATLAS are given, as well as $v_2^{\mathrm{jet}}$ predictions from the JEWEL Monte Carlo, which simulates parton shower evolution in the presence of a dense QCD medium.

Speaker: Redmer Alexander Bertens (Nikhef National institute for subatomic physics (NL))

rbertens_QM2015_v3.pdf

10:50 AM → 12:30 PM Correlations and Fluctuations III

Convener: Sandra Padula (UNESP - Universidade Estadual Paulista (BR))

10:50 AM PHENIX results on fluctuations and Bose-Einstein correlations in Au$+$Au collisions from the RHIC Beam Energy Scan

The RHIC Beam Energy Scan focuses on mapping the QCD phase diagram and pinpointing the location of a possible critical end point. Bose-Einstein correlations and event-by-event fluctuations of conserved quantities, measured as a function of centrality and collision energy, are promising tools in these studies. Recent lattice QCD and statistical thermal model calculations predict that high order cumulants of the fluctuations are sensitive indicators of the phase transition. Products of these cumulants can be used to extract the freeze-out parameters and locate the critical point. Two-pion interferometry measurements are predicted to be sensitive to potential softening of the equation of state and prolonged emission duration close to the critical point. We present recent PHENIX results on fluctuations of net-charge distributions using high-order cumulants and their products in Au$+$Au collisions at $\sqrt{s_{_{NN}}} =7.7$--200~GeV, and measurement of two-pion correlation functions and emission-source radii in Cu$+$Cu and Au$+$Au collisions at several beam energies. The extracted source radii are compared to previous measurements at RHIC and LHC to study energy dependence of the specific quantities sensitive to expansion velocity and emission duration. The experimental results are compared with different heavy-ion-collision models. Implications for the search of critical point, extraction of freeze-out temperatures, and baryon chemical potentials at various collision energies are discussed.

Speaker: Dr Prakhar Garg (Indian Institute of Technology Indore (IN))

Prakhar_QM15_Fluctuations_v2.pdf

11:10 AM Femtoscopy of identified particles in Pb-Pb collisions with ALICE at the LHC

Femtoscopy allows measurements of the space-time characteristics of particle production using correlations resulting from the effects of quantum statistics and final state interactions. We present the results of femtoscopic analyses for different identified particle systems measured by ALICE in Pb-Pb collisions at 2.76 TeV. Hydrodynamic models predict a decrease of the radii with increasing pair transverse $m_T$ due to radial flow. Correlation measurements of heavy particles extend the range over which the transverse mass dependence of the source radii can be studied and thus can serve, as a tool to learn about the dynamics of he deconfined medium. Particularly, we compare the measured 3D kaon radii with a model where the hydrodynamic phase is succeeded by a hadronic rescattering phase and a purely hydrodynamical calculation. The latter predicts an approximate mT scaling of source radii obtained from pion and kaon correlations. This $m_{\mathrm{T}}$ scaling appears broken in our data, which indicates strong rescattering in the hadronic phase at LHC energies. The emission duration and the decoupling time of the system are also estimated using the three-dimensional femtoscopic analysis for kaons, and compared with such estimates obtained from pions.

Speaker: Ludmila Malinina (Joint Inst. for Nuclear Research (RU))

Malinina_QM2015_Sep.pdf

11:30 AM Femtoscopic measurements in p+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV with the ATLAS detector

Recent measurements in two- and multi-particle correlations in p+Pb collisions suggest collective behavior reminiscent of that observed in Pb+Pb. In addition, the data hint at interesting geometric behavior in ultra-central p+Pb events, where fluctuations in the size of the proton may become significant. Femtoscopic measurements may provide useful insight on both of these problems because they image the spatio-temporal size of the particle emitting region. In particular, the evolution of HBT radii with pair momentum should have a characteristic behavior in the presence of collective expansion. This talk will present identical-pion HBT measurements from ATLAS using one- and three-dimensional correlation functions. Pions are identified using $dE/dx$ measured in the pixel detector. Correlation functions and the resulting HBT radii will be presented as a function of pair momentum ($k_T$) and collision centrality. The contribution to the two-particle correlation function from hard processes is studied in depth, and a new method for completely constraining this background will be described. The measured source sizes are observed to decrease with $k_T$ and increase significantly in more central collisions.

Speaker: Markus Kohler (Weizmann Institute of Science (IL))

mkk_QM2015.pdf

11:50 AM Observable consequences of event-by-event fluctuations of HBT radii

One of the major lessons from the field of heavy-ion physics in the past several years has been the significance of the role played by event-by-event fluctuations in the evolution of a heavy-ion collision. Their important effects on many momentum-space observables (particle yields and spectra, anisotropic flows, etc.) have already been studied systematically, and some of the properties of their event-by-event distributions, and their consequences for the extraction of medium properties such as the specific viscosity of the quark-gluon plasma (QGP), are already known. In this talk it is pointed out that similar event-by-event fluctuations of spatiotemporal observables provide complementary constraints on our understanding of the dynamical evolution of heavy-ion collisions. The relation of Hanbury Brown-Twiss (HBT) radii extracted from ensemble-averaged correlation function measurements to the mean of their event-by-event probability distribution is clarified, and a method to experimentally determine the mean and variance of this distribution is proposed and demonstrated using an ensemble of fluctuating events generated with the viscous hydrodynamic code VISH2+1. The sensitivity of the mean and variance of the HBT radii to the specific QGP shear viscosity $\eta/s$ is studied using simulations with the same code. We report sensitivity of the mean pion HBT radii and their variances to the temperature dependence of $\eta/s$ near the quark-hadron transition at a level similar (10-20%) to that which was previously observed for elliptic and quadrangular flow of charged hadrons. References: - Plumberg, C. and Heinz, U. "Interferometric signatures of the temperature dependence of the specific shear viscosity in heavy-ion collisions", Phys.Rev. C91 (2015) 5, 054905 - Plumberg, C. and Heinz, U. "Probing the properties of event-by-event distributions in Hanbury-Brown--Twiss radii", (forthcoming)

Speaker: Christopher Plumberg (The Ohio State University)

QM2015_Plumberg.pdf

12:10 PM Measuring baryon-(anti-)baryon interaction cross-sections with femtoscopy in heavy-ion collisions

Interaction cross-sections for baryon pairs are of fundamental interest and they are actively investigated theoretically. They are known well for pairs of common (anti-)baryons, however there is a lack of precise data for heavier baryons, including the ones carrying strangeness. The two-particle correlation formalism (femtoscopy) is sensitive to the interaction kernel for a pair of particles, which is related to the pair interaction cross-section [1]. We show how this formalism can be used to extract the cross-sections from the femtoscopic baryon-(anti-)baryon correlation functions [2]. The analysis is complicated by the presence of the so-called "residual correlations" arising from weak decay products in the measured sample. We show how this effect can be exploited to gain further insight into the cross-sections of even heavier baryons. We discuss the limitations of the measurement technique and estimate the discovery potential of currently available and soon-to-be-collected heavy-ion collision datasets at RHIC and at the LHC. [1] A. Kisiel, H. Zbroszczyk, M. Szymanski; "Extracting baryon-antibaryon strong interaction potentials from pΛ¯ femtoscopic correlation functions"; Phys.Rev. C89 (2014) 5, 054916 [2] R. Lednicky, V.L. Lyuboshits; "Final State Interaction Effect on Pairing Correlations Between Particles with Small Relative Momenta"; Sov.J.Nucl.Phys. 35 (1982) 770, Yad.Fiz. 35 (1981) 1316-1330

Speaker: Adam Kisiel (Warsaw University of Technology (PL))

AKisiel_QM2015.pdf

10:50 AM → 12:30 PM Collective Dynamics II

Convener: Chiho Nonaka (Nagoya University (JP))

10:50 AM Anisotropic hydrodynamics for conformal Gubser flow

We derive the equations of motion for a system undergoing boost-invariant longitudinal and azimuthally-symmetric transverse "Gubser flow" using leading-order anisotropic hydrodynamics. This is accomplished by assuming that the one-particle distribution function is ellipsoidally-symmetric in the momenta conjugate to the de Sitter coordinates used to parameterize the Gubser flow. We then demonstrate that the SO(3)_q symmetry in de Sitter space further constrains the anisotropy tensor to be of spheroidal form. The resulting system of two coupled ordinary differential equations for the de Sitter-space momentum scale and anisotropy parameter are solved numerically and compared to a recently obtained exact solution of the relaxation-time-approximation Boltzmann equation subject to the same flow. We show that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches. In addition, we prove that anisotropic hydrodynamics gives the exact solution of the relaxation-time approximation Boltzmann equation in the ideal, eta/s -> 0, and free-streaming, eta/s -> infinity, limits.

Speaker: Michael Strickland (Kent State University)

strickland.pdf

11:10 AM Decorrelation of anisotropic flow along the longitudinal direction

The decorrelation of 2nd and 3rd order anisotropic flow along longitudinal direction with large pseudorapidity η gap is investigated in event-by-event (3+1)D ideal hydrodynamics with fluctuating initial conditions from A MultiPhase Transport (AMPT) model. The agreement between our results and CMS data for all available centralities in Pb+Pb collisions at LHC suggests that the string model used in Pythia and Hijing captures most features of the initial state fluctuations along longitudinal direction.The predictions for Au+Au collisions at RHIC are provided and give a much stronger longitudinal decorrelation, indicating larger fluctuations along the pseudorapidity direction for lower energy collisions. Further detailed studies show that the decorrelation of final charged hadrons in momentum space comes from initial state decorrelation in space, while the hydrodynamic evolution is important to transfer the decorrelation in coordinate space to momentum space. We also demonstrate that this breakdown of the flow factorization is an important ingredient towards understanding the longitudinal structure in the initial state of high energy heavy ion collisions.

Speaker: LongGang Pang (Lawrence Berkeley National Laboratory)

QM2015_LongGang.pdf

11:30 AM Hydrodynamic fluctuations and dissipation in an integrated dynamical model

Thermal fluctuations arising during hydrodynamic evolution of the system (a.k.a., *hydrodynamic fluctuations*) [1] play an important role in event-by-event hydrodynamic simulations. For example, entropy production fluctuates during the expansion even if we start from a common initial condition in a macroscopic sense [2]. On the other hand, the effect of the fluctuations must be significant in small colliding systems such as p-p, p-A and peripheral A-A collisions [2]. Stability of thermal equilibrium systems is a consequence of an interplay between thermal fluctuations and dissipation. Thus it is indispensable to take the hydrodynamic fluctuations into account in causal dissipative hydrodynamic simulations. In this study, we develop a new (next-generation) integrated dynamical model to investigate the effects of the hydrodynamic fluctuations on observables in high-energy nuclear collisions. We implement the hydrodynamic fluctuations in a fully 3-D dynamical model consisting of the hydrodynamic initialization models such as Monte-Carlo Kharzeev-Levin-Nardi model and Monte-Carlo Glauber model, causal dissipative hydrodynamics, and the subsequent hadronic cascades. By analyzing the hadron distributions obtained by massive event-by-event simulations with both of the hydrodynamic fluctuations and the initial-state fluctuations, we discuss the effects of the hydrodynamic fluctuations on the flow harmonics, $v_n$, and their fluctuations. This sheds a new light on extracting transport coefficients from observables. * [1] K. Murase and T. Hirano, arXiv:1304.3243 [nucl-th]. * [2] T. Hirano, R. Kurita, K. Murase and K. Nagai, Nucl. Phys. A **931** (2014) 831.

Speaker: Koichi Murase (The University of Tokyo)

20150929v2.murase.pdf

20150929v2.murase.pptx

(appendix) 20150929.murase-plots.tar.gz

11:50 AM The Rapidity Density Distributions and Longitudinal Expansion Dynamics of Identified Pions from the STAR Beam Energy Scan

The Beam Energy Scan (BES) at the Relativistic Heavy-Ion Collider was proposed to characterize the properties of the medium produced in heavy-ion interactions over a broad range of baryon chemical potential. The aptitude of the STAR detector for mid-rapidity measurements has previously been leveraged to measure identified particle yields and spectra to extract bulk properties for the BES energies in this kinematic window. However, to extract information on expansion dynamics and full phase space particle production it is necessary to study identified particle rapidity density distributions. In this talk, we present the first rapidity density distributions of identified pions from Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, and 19.6 GeV from the Beam Energy Scan program as measured by the STAR detector. We use these distributions to obtain the full phase space yields of the pions to provide additional information of the system's chemistry. Further, we report the width of the rapidity density distributions compared to the width expected from Landau hydrodynamics. Finally, we interpret the results as a function of collision energy and discuss them in the context of previous energy scans done at the AGS and SPS.

Speaker: Chris Flores

QuarkMatter2015_Flores_v6.pdf

12:10 PM Studies on longitudinal fluctuations of anisotropy flow event planes in PbPb and pPb collisions at CMS

Most studies of anisotropy flow phenomena have assumed a global flow phase angle (or event plane angle) that is boost invariant in pseudorapidity ($\eta$). It was realized in recent years that this assumption may not be valid in presence of initial-state fluctuations, especially along the longitudinal direction. The effect of eta-dependent event plane fluctuations would break the factorization relation of Fourier coefficients from two-particle azimuthal correlations into a product of single-particle anisotropy Fourier harmonics as a function of $\eta$. First study of factorization breakdown effect in $\eta$ is carried out using the CMS detector, which covers a wide $\eta$ range of 10 units. A novel method is employed to suppress nonflow correlations at small pseudorapidity gaps of two particles. Significant eta-dependent factorization breakdown is observed in both PbPb and high-multiplicity pPb collisions. The measurements are presented for various orders of flow harmonics as a function of centrality or event multiplicity classes in PbPb and pPb, and are also compared to three-dimensional hydrodynamic calculations with longitudinal fluctuations. The new results presented here provide new insights into the longitudinal dynamics of relativistic heavy ion collisions, and help improve the three-dimensional modeling of the evolution of the strongly-coupled quark gluon medium.

Speaker: Maxime Guilbaud (Rice University (US))

QM2015talk.pdf

10:50 AM → 12:30 PM Open Heavy Flavors and Strangeness IV

Convener: Paolo Giubellino (Universita e INFN Torino (IT))

10:50 AM Heavy quark suppression and D-hadron (D-D) correlations in heavy-ion collisions

Heavy quarks are valuable probes of the dense nuclear matter produced in relativistic heavy-ion collisions. We establish a comprehensive framework that describes their entire temporal evolution in the QGP matter and the subsequent hadron gas. The dynamics of open heavy quarks in the QGP is described using either an improved Langevin approach [1,2] or a linearized Boltzmann approach [3] that both simultaneously incorporate the quasi-elastic scattering and medium-induced gluon radiation processes. The hadronization of heavy quarks into their mesonic bound states is calculated utilizing our hybrid model of fragmentation plus heavy-light quark coalescence [1,2]. And the final rescatterings of heavy hadrons inside the hadron gas are described using the UrQMD model. Within this newly developed framework, we demonstrate that while quasi-elastic scattering dominates heavy quark energy loss in the QGP at low energies, contributions from gluon radiation at high energies are significant; and the coalescence process is found important for heavy meson production at intermediate $p_\rm{T}$. Our numerical results provide a good description of the $R_\rm{AA}$ and $v_2$ of both $D$ meson and $B$-decay non-prompt $J/\psi$ measured at RHIC and LHC. In addition, two-particle correlation functions of heavy flavor are explored [4]. We show that while the nuclear modification of the $p_\rm{T}$ imbalance of $D-\bar{D}$ pairs reflects the total energy loss of heavy quarks, their angular correlations are sensitive to the detailed energy loss mechanisms. $D$-hadron correlations are also calculated and shown to be a potential observable quantifying the medium response to the energy deposited by hard probe particles. [1] S. Cao, G.-Y. Qin, and S. A. Bass, Phys. Rev. C88, 044907 (2013). [2] S. Cao, G.-Y. Qin, and S. A. Bass, arXiv: 1505.01413. [3] Y. He, T. Luo, X.-N. Wang and Y. Zhu, Phys. Rev. C91 054908 (2015). [4] S. Cao, G.-Y. Qin, and S. A. Bass, arXiv: 1505.01869.

Speaker: Shanshan Cao (Lawrence Berkeley National Lab)

QM2015-Shanshan.pdf

QM2015-Shanshan.pdf

QM2015-Shanshan.pptx

11:10 AM Measurements of $D_{s}^{\pm}$-meson $R_{CP}$ and $v_{2}$ in Au+Au collisions at $\sqrt{s_{NN}}$ =200 GeV in STAR

Heavy quarks are considered as an excellent probe for the early dynamics in heavy-ion collisions. Among all open charm mesons, $D_{s}^{+}(c\bar s)$ and $D_{s}^{-}(\bar c s)$ mesons play a unique role to quantify heavy quark diffusion and hadronization in heavy-ion collisions, because of their valence quark compositions. Also, like multi-strange hadrons, $D_{s}^{\pm}$ mesons are expected to freeze out early and have smaller hadronic interaction cross-section compared with other $D$ mesons. Therefore, the elliptic flow ($v_{2}$) of $D_{s}^{\pm}$ is considered to be a better measure of the partonic contribution to the charm hadron $v_{2}$ than that of $D^{0}$ or $D^{\pm}$. The new Heavy Flavor Tracker detector, which has been installed recently in the STAR experiment, provides a unique opportunity to reconstruct $D_{s}^{\pm}$ via displaced vertices at RHIC at $\sqrt{s_{NN}}$ =200 GeV. We will present the first measurement of the nuclear modification factor $R_{CP}$ and $v_{2}$ of $D_{s}^{\pm}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. These results will be compared with those of other open charm mesons and strange mesons to determine how the (possibly) strangeness equilibrated partonic matter affects the $D_{s}^{\pm}$ meson production. They will also be compared with measurements at the LHC energy to study the energy dependence of the above mentioned phenomena.

Speaker: Nasim Md (Uiniversity of california, Los Angeles)

QM15_Ds_nasim.pdf

QM15_Presentation_Ds_Nasim.pdf

11:30 AM Measurements of Open Heavy Flavor Production in Semi-leptonic Channels in p+p, U+U and Au+Au Collisions at STAR

Heavy flavor quarks are suggested as excellent probes to study the strongly interacting Quark-Gluon Plasma (QGP) discovered in high-energy heavy-ion collisions. Measurements of heavy flavor production will advance our understanding of the properties of the QGP. Studies in different heavy-ion collision systems and centralities, and separately for charm and bottom quarks can provide new insights in how partons interact with the QGP, and QGP evolution and dynamics. In this talk, we will present the most recent results on Non-Photonic Electron (NPE) production from semi-leptonic decays of open heavy flavor hadrons with the STAR experiment at the Relativistic Heavy Ion Collider. We will first report updated results on NPE production in p+p collsions at $\sqrt{s}$= 200 GeV with much improved precision and wider kinematic coverage than previous ones. These results are instrumental to test the validity of perturbative QCD calculations, and provide precise references for heavy-ion collisions. Calculations suggest that a 20% higher Bjorken energy density may be reached in U+U collisions, which can lead to a stronger suppression for NPE production. We will also report new results on the nuclear modification factor, $R_{AA}$, for NPE production in the 0-5% most central U+U collisions at $\sqrt{s_{NN}}$=193 GeV and compare with those in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. Finally we will report the most recent development in measurements of NPE from open bottom and charm hadron decays separately, utilizing the new Heavy Flavor Tracker of the STAR experiment.

Speaker: Xiaozhi Bai (University of Illinois at Chicago)

QM2015_xiaozhi.pdf

11:50 AM PHENIX results on heavy-flavor yields at forward rapidity

PHENIX installed and commissioned a forward silicon vertex tracker (FVTX) in 2012. The complete detector covers the rapidity range of $1.2 < |y| < 2.2$, and each arm has full azimuthal coverage. This acceptance matches that of the PHENIX muon arms. With the barrel silicon vertex detector, the FVTX greatly improves tracking to the collision vertex, and is able to identify secondary particles from in-flight decays. We present the current status of the analysis of $c$ and $b$ production in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV using the distance of closest approach to the event vertex of inclusive decay muons, and of $b$ production from J/$\psi$ decay. We will also show the current status of a study of $\psi^{\prime}$ production in Cu$+$Au collisions. Preliminary results on a reference measurement of $\psi^{\prime}$ in $p$$+$$p$ collisions at $\sqrt{s} = 510$~GeV will be shown. The $c$ and $b$ yields in Cu$+$Au collisions provide insight into the rapidity dependence of energy loss of heavy flavor in hot nuclear matter. The Cu$+$Au collisions also offer the opportunity to study $\psi^{\prime}$ dissociation relative to that of the J/$\psi$ as a function of path length in the nuclear medium.

Speaker: Melynda Brooks (Los Alamos National Laboratory)

QuarkMatter2015_HeavyFlavor_Brooks_forpdf.pdf

12:10 PM RAA and v2 of muons from heavy-quark decays in lead-lead collisions at sqrt(sNN)=2.76TeV with the ATLAS detector

The ATLAS measurement of the nuclear modification factor (RAA) and the elliptic flow (v2) of muons from heavy quark decays in Pb+Pb collisions at sqrt(s_NN)= 2.76 TeV are presented. The measurements are done over the pT range of 4-14 GeV and over the centrality range of (0-60)% within pseudorapidity interval of |η|<1.  A significant elliptic flow is observed over the full pT range for all centralities. The RAA results are consistent with previous measurements but have much better statistical precision. More than a factor of two suppression of the muon yield relative to scaled pp data is observed in the most central collisions. These measurements give an insight into the interaction of heavy quarks with the bulk medium produced in heavy-ion collisions.

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

atlas_muon_RAA_v2_sasha_v4.pdf

12:30 PM → 2:00 PM Lunch

2:00 PM → 4:20 PM Jets and High pT Hadrons IV

Convener: Yves Schutz (IN2P3 (FR) and CERN)

2:00 PM Dynamical energy loss as a novel tomographic tool of QGP at RHIC and LHC

High momentum suppression of light and heavy flavor observables is considered to be an excellent probe of jet-medium interactions in QCD matter created at RHIC and LHC. Utilizing this tool requires accurate suppression predictions for different experiments, probes and experimental conditions, and their unbiased comparison with experimental data. With this goal, we developed the dynamical energy loss formalism towards generating predictions for non-central collisions; the formalism takes into account both radiative and collisional energy loss computed within the same theoretical framework, dynamical (as opposed to static) scattering centers, finite magnetic mass, running coupling and uses no free parameters in comparison with experimental data. Within this formalism, we will provide predictions, and a systematic comparison with experimental data, for a diverse set of suppression data: all available light and heavy flavor probes, lower and high momentum ranges, various centrality ranges and various collision energies at RHIC and LHC. We will also provide clear qualitative and quantitative predictions for the upcoming RHIC and LHC experiments. Comprehensive agreement between our predictions and experimental results provides us with a good deal of confidence that our dynamical energy loss formalism can well explain the jet-medium interactions in QGP, which will be further tested by the obtained predictions for the upcoming data. Application of this model, as a novel high-precision tomographic tool of QGP medium, will also be discussed.

Speaker: Magdalena Djordjevic (Institute of Physics Belgrade)

MagdalenaDjordjevic_QM2015.pdf

2:20 PM Jet Formation and Interference in Quark Gluon Plasma

We study the double inclusive emission of gluons off a hard parton propagating in thin QCD plasma. Within the N=1 opacity approximation, we determine the induced emission pattern of two gluons which are soft compared to the parton energy but hard compared to the medium scale. We assume a wide separation between the energies of those two gluons, but we allow arbitrary ordering of their emission angles. We select the transverse momenta of the induced gluons such that only the softest one may be medium induced. We study the ordering properties of a hard jet forming in the medium by analyzing the interference pattern of the softest gluon with respect to the hard quark-gluon core. We concentrate in the regime in which the formation times of both gluons are comparable and discuss the interplay between interferences and the formation time of the quark-gluon subsystem.

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

JCS_talk.pdf

2:40 PM PHENIX results on reconstucted jets in $p$$+$$p$ and heavy ion collisions

PHENIX has measured the inclusive jet cross-section at midrapidity in $p$$+$$p$ collisions at $\sqrt{s_{NN}}$=200 GeV. Jets were reconstructed from charged particles and electromagnetic calorimeter clusters using the anti-$k_T$ algorithm with $R=0.3$ and a Gaussian filter reconstruction algorithm. These small radii jet reconstructions are needed as baseline measurements for comparisons with heavy ion collisions. The measurements are unfolded for detector effects and the resulting jet spectra are reported for the transverse momentum range $8<p_T<60$ GeV/$c$. These results are compared with theoretical calculations with implications for the sensitivity to the gluon angular emission. Results on reconstructed jets in $d$$+$Au and Cu$+$Au collisions at the same $\sqrt{s_{NN}}$=200 GeV are reported and nuclear modification factors $R_{AA}$ compared to those measured via single inclusive hadrons. These results probe the interplay between descriptions of the collision geometry and hard processes, and partonic energy loss in a heavy-ion collision with novel geometry, respectively.

Speaker: Arbin Timilsina (ISU)

QM15_Jets_Timilsina.pdf

3:00 PM Semi-inclusive charged jet measurements in Au+Au collisions at \sqrt{s_{NN}} = 200 GeV with STAR

In this talk we report measurements by the STAR collaboration of the semi-inclusive yield and azimuthal distribution of reconstructed charged jets recoiling from a high p_{T} hadron trigger, in central and peripheral Au+Au collisions at \sqrt{s_{NN}} = 200 GeV. Corrections for the large underlying background to jet observables in heavy-ion collisions are carried out on an ensemble-averaged basis using a novel event-mixing technique, without imposition of a fragmentation bias on the reported jet population. Charged recoil jets with a transverse momentum up to 34 GeV/c are reported without a low-p_{T} cutoff, for jet radii up to R=0.5. We compare the measurements to theoretical calculations and to similar jet measurements at the LHC. These measurements provide insight into the nature of jet quenching, and may probe the quasi-particle degrees of freedom in the Quark-Gluon Plasma.

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

STAR_hJet_Jacobs_final.pdf

STAR_hJet_Jacobs_final.pptx

3:20 PM Measurement of high $p_{\rm T}$ photons and neutral mesons in $pp$ and Pb-Pb collisions at mid-rapidity with ALICE

The ALICE experiment at the LHC performs measurements of neutral meson and direct photon inclusive spectra at mid-rapidity in a wide $p_{\rm T}$ range in $pp$, $p$-Pb and Pb-Pb collisions. Photons and neutral mesons ($\pi^{0}$, $\eta$, $\omega$) are reconstructed via complementary methods, using the ALICE electromagnetic calorimeters, PHOS and EMCal, and by the central tracking system, identifying photons converted into $e^+e^-$ pairs in the material of the inner barrel detectors (TPC and ITS). Prompt direct photons produced in Compton ($q+g \rightarrow \gamma+q$) and annihilation ($q+\bar{q} \rightarrow \gamma+g$) processes can be identified in the EMCal calorimeter combining two techniques: electromagnetic shower shape analysis; and isolation cut analysis (no other particle production along the photon direction in the hard process), making use of the measured particle activity in the EMCal and in reconstructed tracks close to the prompt photon candidate. These methods are efficient in getting rid of photons from neutral meson decays ($\pi^{0}$ and $\eta$), dominant at high-energy collisions produced at LHC. Measurements of isolated photons and neutral meson spectra in pp collisions provide valuable data for pQCD calculations and allow us to study scaling properties of hadron production at LHC energies and to constrain the proton parton distribution function. ALICE measured the nuclear modification factor $R_{\rm AA}$ for the $\pi^{0}$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV at different collision centralities showing a clear pattern of strong suppression in a hot QCD medium with respect to $pp$ collisions. In this presentation, we will show $\pi^{0}$ and $\eta$ spectra in $pp$ and Pb-Pb collisions and isolated photon spectra in $pp$ collisions up to high $p_{\rm T}$. These results will be compared to state-of-the art theoretical predictions.

Speaker: Astrid Morreale (Centre National de la Recherche Scientifique (FR))

morreale-QM-2015.pdf

3:40 PM Jet suppression and the flavor dependence of partonic energy loss with ATLAS

In relativistic heavy ion collisions, a hot medium with a high density of unscreened color charges is produced. One manifestation of the energy loss of jets propagating through the medium is a lower yield of jets emerging from the medium than 
expected in the absence of medium effects. Therefore modifications of the jet yield are directly sensitive to the energy loss mechanism. Furthermore, jets with different 
flavor content are expected to be affected by the medium in different ways. Parton showers initiated by quarks tend to have fewer fragments carrying a larger fraction of 
the total jet energy than those resulting from gluons. Jets containing heavy quarks may lose less energy as the large quark mass suppresses the amount of medium-induced 
radiation. This would lead to different relative contributions of inelastic and elastic energy loss. In this talk, the latest ATLAS results on single jet suppression will 
be presented. Measurements of the nuclear modification factor, RAA, for fully reconstructed jets are shown. The rapidity dependence of jet suppression is discussed, which 
is sensitive to the relative energy loss between quark and gluon jets. New measurements of single hadron suppression out to pT~150 GeV are also presented, which provide 
complementary information to the jet suppression measurements. Finally, a new measurement of the RAA for b-tagged jets is presented. At low b-jet pT, the role of the 
heavy quark mass is expected to be maximal and b-jets are dominated by hard scattering processes where the b quark carries most of the momentum. As the jet pT increases, 
the flavor dependence of the energy loss is expected to be reduced and a significant contribution to b quark production develops from gluon splitting in the parton shower. 
This measurement covers a kinematic range including both regimes and the interplay between the various effects is discussed.

Speaker: Tomas Kosek (Charles University (CZ))

QM2015_tkosek_slides.pdf

4:00 PM New results on inclusive and reaction plane dependent dijet asymmetry in Pb+Pb collisions with ATLAS

The phenomenon of events containing highly asymmetric dijet pairs is one of the most striking results in heavy ion physics. It has provided the first direct observation of in-medium jet energy loss at the LHC. Detailed measurements of centrality-dependent dijet imbalance in $\sqrt{s_{NN}}=2.76$ TeV PbPb collisions using data collected in the 2011 LHC heavy ion run are presented. The new analysis fully corrects to the particle level. The results show a centrality-dependent modification of the dijet asymmetry distribution accompanied by an unmodified angular correlation between two jets in the dijet system. Detailed studies of the dijet asymmetry as a function of the leading jet transverse momentum and jet radius are presented. The reference measurement of the dijet asymmetry in the pp collisions at the same center of mass energy is also shown. The dijet asymmetry measurements are also done while selecting the leading jet at different angles with respect to the second order event-plane. This effectively probes the path-length dependence of the dijet asymmetry at fixed centrality. The variation of the dijet asymmetry with the soft particle $v_2$, at fixed centrality are also measured. To further constrain the energy loss models, the measurement of the correlations between jets that are at small relative angles was performed. The measured neighbouring jet pairs result primarily from hard radiation by the parton that occurs early in the process of the shower formation. These dijet and multijet measurements can provide a better understanding of the correlation of the parton energy-loss with the underlying geometry, help elucidating the role of the fluctuations in the energy loss as well as put some constrains to models in which a part of the parton shower radiates coherently in the response of the medium.

Speaker: Dennis Vadimovich Perepelitsa (Brookhaven National Laboratory (US))

dvp-QM15-ATLAS-9-29-15.pdf

2:00 PM → 4:20 PM Correlations and Fluctuations IV

Convener: Fuqiang Wang (Purdue University (US))

2:00 PM Magnetihydrodynamics and charged flow in non-central heavy ion collisions

Strong magnetic fields produced in any non-central heavy ion collision are expected to affect the dynamics of the hot QCD matter produced in this collision. The magnetic field is time-dependent and the conducting medium is expanding, which leads to the induction of charged currents due to the combination of Faraday and Hall effects. We extend our previous work by studying the imprint of the magnetic fields produced in non-central heavy ion collisions on the azimuthal distributions and correlations of the produced charged hadrons by employing a hydrodynamic description of the expanding cooling droplet of liquid produced in a heavy ion collision combined with the electromagnetic effects in a perturbative fashion. We use the Cooper-Frye freeze-out procedure to obtain the azimuthal hadron distributions. We find that the charged currents induced by the presence of the electromagnetic fields result in a charge-dependent directed flow $v_1$, elliptic flow $v_2$ and triangular flow $v_3$ that is respectively odd, even, odd in rapidity and always odd under charge exchange. It can be detected by measuring correlations between the directed, elliptic and triangular flow of charged hadrons at different rapidities, $\langle v_i(y_1)v_i(y_2)\rangle$. We also investigate the dependence of our model on the various parameters and make estimates of the magnitude of the charge-dependent flow observables expected at RHIC and the LHC.

Speaker: Umut Gursoy (Utrecht University)

Magnetic-currents-Kobe.pdf

2:20 PM Charge-dependent correlations from event-by-event anomalous hydrodynamics

The chiral magnetic effect (CME) has received considerable attention in recent years, particularly in the context of heavy-ion collisions. The anomaly-induced transport effects like the CME are macroscopic and are incorporated into hydrodynamic equations giving rise to "anomalous hydrodynamics". Theoretically, the CME is expected to occur in heavy-ion collisions. The data reported by STAR[1] and PHENIX[2] collaborations at RHIC and ALICE collaborations [3] at the LHC show a behavior consistent with the CME, but the quantitative understanding is still lacking. In order to reach a definitive conclusion, a reliable theoretical tool that can describe the charge-dependent observables is indispensable. In this contribution, we report our recent attempt of quantitative modeling of the CME for heavy-ion collisions. We develop an event-by-event hydrodynamic model which includes the anomalous transport effects. We perform 3+1 dimensional anomalous hydrodynamic simulations, with constitutive equations that contain the anomaly-induced effects. We also develop a model of the initial condition for the axial charge that captures the statistical nature of random chirality imbalance created by color flux tubes. Basing on the event-by-event hydrodynamic simulations for hundreds of thousands of collisions, we calculate the correlation functions that are measured in experiments, and discuss how the anomalous transports affect the observables. [1] B. I. Abelev et al. [STAR Collaboration], Phys. Rev. Lett. 103, 251601 (2009); B. I. Abelev et al. [STAR Collaboration], Phys. Rev. C 81, 054908 (2010). [2] A. Ajitanand, S. Esumi, R. Lacey [PHENIX Collaboration], Proc. of the RBRC Workshops, vol. 96, 2010. [3] P. Christakoglou [ALICE Collaboration] 2011 J. Phys. G: Nucl. Part. Phys. 38 124165. [4] Y. Hirono, T. Hirano, and D. E. Kharzeev, [arXiv:1412.0311]

Speaker: Yuji Hirono (Stony Brook University)

qm15-hirono.pdf

qm15-hirono.pptx

2:40 PM The ridge and di-hadron correlations from the Beam Energy Scan at RHIC

Di-hadron correlations are a key observable in heavy-ion collisions, and play a critical role in establishing the equation of state for hot and dense matter. Long range di-hadron correlations, also known as the ridge, have been observed at the top RHIC energies and the LHC in A+A, p+A, and d+A collisions and are crucial to probing the collectivity of the various systems. We will present the first set of results of 2D di-hadron correlations ($\Delta \phi,\Delta \eta$) for Au+Au collisions with center-of-mass energies 7, 11.5, 14.5, 19.6, 27, and 39 GeV from the STAR experiment. Measurements of these correlations will utilize both the TPC and FTPC to provide extensive coverage in azimuth and pseudo-rapidity, where the ranges extend to $0 < \phi < 2\pi$ and $0 < |\eta| < 4$ respectively and are integrated over $0.2<p_T<2.0$ GeV/c. We will obtain anisotropy coefficients of orders 2-5 ($v_{2-5}\{2\}$) from the ridge, and show how they depend on energy and centrality. In particular, when scaled by the multiplicity, we find $v_3\{2\}$ shows a non-monotonic behavior as a function of energy. Hints of similar behavior are observed when $v_3\{2\}$ and $v_4\{2\}$ are scaled by $v_2\{2\}$. We will discuss the relevance of this observation in terms of a possible pressure minimum, and how such a minimum might relate to critical point searches in the Beam Energy Scan. Finally, we will analyze the near-side peak, which could be narrowed in the presence of radial flow, via studying its beam-energy and centrality dependence.

Speaker: Liao Song (University of Houston)

QM2015LIAOFINAL.pdf

3:00 PM Forward-backward multiplicity fluctuation and longitudinal harmonics in high-energy nuclear collisions

One of the largest uncertainties in the modeling of heavy-ion collision arises from present poor understanding of the early-time dynamics especially in the longitudinal direction. Forward-backward (FB) multiplicity correlation has been regarded as a power observable on the early time dynamics since it probe directly the initial state density fluctuations in pseudorapidity. Previous studies of FB multiplicity correlation were primarily based on two-bin or multi-bin correlation method in selected $\eta$ ranges, whose connection to underlying dynamics is complicated by statistical smearing due to finite multiplicity and residual centrality or volume effects. In a recent paper (1506.03496), we have developed a data-driven two-particle correlation method which overcome both limitations and hence allow direct connection between the correlation function and underlying heavy-ion collision dynamics. The robustness and physics potential of the method are demonstrated using the AMPT and HIJING simulation. We found that the long-range component of the FB correlation is captured by a few longitudinal harmonics, with the first component driven by the asymmetry in the number of participating nucleons in the two colliding nuclei and the second component reflecting the EbyE fluctuation of nuclear-stopping. The higher-order longitudinal harmonics are found be strongly damped in AMPT compare to HIJING, due to weaker short-range correlations as well as the final-state effects present in the AMPT model. Two-particle pseudorapidity correlation reveals interesting charge-dependent short-range structures in AMPT model that are absent in HIJING model. The proposed method opens a new avenue to elucidate the particle production mechanism and early time dynamics in heavy-ion collisions. Future analysis directions and prospects of using the pseudorapidity correlation function to understand the centrality bias in p+p, p+A and A+A collisions are discussed.

Speaker: Peng Huo (State University of New York (US))

qm15_PengHuo.pdf

3:20 PM Measurement of two-particle pseudorapidity correlations in proton-lead and lead-lead collisions with the ATLAS detector

Two-particle pseudorapidity correlations are measured using charged particles from sqrt(s_NN)=2.76 TeV Pb+Pb collisions by the ATLAS experiment at the LHC. The correlation function CN(η1, η2) is measured for different centrality intervals for | η1, η2|<2.4 and transverse momentum pT>0.5 GeV. An enhancement is observed along η- =η1-η2 ≈0 and a suppression is observed at large η- values. The correlation function is expanded in Legendre polynomials, and root-mean-square values of the Legendre coefficients at the single particle level an are measured. Significant values are observed for an, which decrease quickly for larger n. The leading coefficient a1 is compared to that estimated from a fit to CN(η+) for different η- slices, as well as to the asymmetry of the number of participating nucleons between the two colliding nuclei ANpart = (NpartF-NpartB)/ (NpartF+NpartB). The centrality dependence of a1 show a very similar shape as ANpart in mid-central collisions (20-50%), but show faster increase in more central and more peripheral collisions. The latter behavior suggests additional forward-backward multiplicity fluctuations that may arise from fluctuations at the sub-nucleonic level. The status of a similar measurement in proton-lead collisions will be reported. The implications of these measurements for constraining the early time dynamics of high-energy nuclear collisions are discussed.

Speaker: Jiangyong Jia (State University of New York (US))

JiangyongJia_qm2015_v7.pdf

JiangyongJia_qm2015_v7.pptx

3:40 PM Forward-central two-particle correlations in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

A double-ridge structure has been observed in two-particle correlations in p-Pb collisions at midrapidity and its origin is actively debated. Measurements at larger relative pseudorapidity can further improve our understanding of this phenomenon. The results on two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 < |η| < 4.0) and associated particles at mid-rapidity (|η| < 1.0) in p-Pb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV are reported in the talk. The trigger particles are detected by the ALICE muon spectrometer, and the associated particles by the ALICE central barrel tracking detectors. The reconstructed trigger particles mainly originate from weak decays of primary pions and kaons at low transverse momentum ($p_T$), and heavy-flavor particles at high $p_T$. The ridge is found to persist to the pseudorapidity ranges studied here, and the second-order Fourier coefficients for these measured trigger particles are extracted after subtracting the correlations obtained in low-multiplicity events from those in high-multiplicity events. The Fourier coefficients have a similar pT dependence in the p-going and Pb-going directions, and the ratio of Fourier coefficients in the two directions is calculated as a function of $p_T$. The results are compared with calculations from a parton-cascade model.

Speaker: Evgeny Kryshen (CERN)

2015-09-29-kryshen-qm-final.pdf

4:00 PM Multiplicity and transverse momentum dependence of electric charge balance functions

We report comprehensive results on the balance function as a function of the pseudorapidity and azimuthal angle difference, ∆η and ∆φ respectively, between two charged particles. Results on the multiplicity and transverse momentum ($p_T$) dependence measured with ALICE in pp, p-Pb, and Pb-Pb collisions at 7 TeV, 5.02 TeV, 2.76 TeV are presented. The balance function in both ∆η and ∆φ becomes narrower with increasing multiplicity in all three systems for particles with 0.2 < pT < 2.0 GeV/c. The experimental findings favor models that either incorporate some collective behavior (e.g. AMPT) or mimic this using different mechanisms (e.g. PYTHIA8 with color reconnection). For higher values of transverse momenta the balance function becomes even narrower but exhibits no quantitative difference between the three systems. The results add constraints to models that describe collective effects down to small systems (for low values of $p_T$), and particle production mechanisms such as coalescence and fragmentation processes (for inter- mediate and high values of $p_T$).

Speaker: Panos Christakoglou (Nikhef National institute for subatomic physics (NL))

Christakoglou.Alice.QM2015.pdf

2:00 PM → 4:20 PM QGP in Small Systems II

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

2:00 PM PHENIX results on collectivity tests in high-multiplicity $p$$+$$p$ and $p$$+$Au collisions

Observations of possible collective effects in high-multiplicity $p$$+$$p$ collisions at the LHC and in $p$$+$Pb and $d$$+$Au collisions at the LHC and RHIC challenge our understanding of the requirements for quark-gluon plasma formation. To further investigate this, PHENIX recorded high statistics $p$$+$$p$ and $p$$+$Au data sets in 2015. In both cases, high-multiplicity triggers were implemented using the forward silicon detector (FVTX) and the beam-beam counter (BBC) covering pseudorapidity $1.0<|\eta|<3.0$ and and $3.1<|\eta|<3.9$, respectively. The large high-multiplicity event samples enable highly differential analyses to look for collective effects. We report results on large pseudo-rapidity-separation correlations investigating whether the near-side ridge is seen in high-multiplcity $p$$+$$p$ events at RHIC. We also report the extraction of flow coefficients from azimuthal anisotropies in $p$$+$Au and compare the results with theoretical expectations, including viscous hydrodynamics where the elliptic flow strength is expected to be substantially smaller than in $d$$+$Au and $^3$He$+$Au at the same energy.

Speaker: itaru nakagawa (RIKEN)

QM2015_itaru_150929_v1.1.pdf

QM2015_itaru_150929_v1.1.pptx

QM2015_itaru_150929_v1.1.pptx

2:20 PM To Be (Collective) or Not to Be (Collective) - Different Theoretical Approaches to Describing Small Collisions System Observables

We have investigated the hypothesis that small collision systems (p+A, d+A, 3He+A) at RHIC and the LHC form small droplets of nearly inviscid quark-gluon plasma within the context of hydrodynamic models (Phys.Rev.Lett. 113 (2014) 11, 112301) and with an extension of the AMPT model (arXiv:1501.06880). We explore the constraints on such pictures and the geometric scaling by varying the hydrodynamic viscosity and transition to hadronic cascade, and in AMPT by varying the initial geometry and parton-parton interaction strength. These studies also motivate a beam-energy scan of small systems that may be carried out at RHIC in 2016. We detail predictions for the various observables in this new energy regime. These studies can provide experimental and theoretical handles for elucidating the relevant physics behind small system collectivity with important implications on such observations in large system collisions.

Speaker: Jamie Nagle (University of Colorado Boulder)

nagle_quarkmatter_smallcollectivity_2015.pdf

nagle_quarkmatter_smallcollectivity_2015.pptx

2:40 PM Measurement of the long-range azimuthal correlations in pp collisions at sqrt(s)=13TeV with the ATLAS detector at the LHC

The ATLAS measurement of azimuthal correlations between particle pairs at large pseudorapidity separation in pp collisions at sqrt(s)=13 TeV are presented. The data were collected using a combination of the minimum-bias and high track-multiplicity triggers. A detailed study of the dependence of two-particle correlations on the charged particle multiplicity, transverse momentum of the pair constituents and the pseudorapidity separation between particles forming a pair is shown. Measurements of multi-particle cumulants in the azimuthal angles of produced particles in wide pseudorapidity (|η|<2.5) and multiplicity ranges, with the aim to extract a single particle anisotropy coefficient, v2, are also presented. These measurements can help to understand the origin of the long-range correlations seen in high-multiplicity pp and p+Pb collisions.

Speaker: Mingliang Zhou (State University of New York (US))

QM15_Mingliang_ppRidge_ver9.pdf

3:00 PM Azimuthal anisotropy harmonics from long-range correlations in high multiplicity pp collisions at CMS

Observation of a long-range, near-side, two-particle correlation (known as the “Ridge”) in high-multiplicity pp and pPb collisions opened up new opportunities of exploring novel QCD dynamics in small collision systems. While extensive studies of this long-range correlation phenomenon in pPb collisions have revealed its collective properties, the nature of the ridge in pp collisions still remains unknown. New measurements of two-particle angular correlations for charged particles, and identified $K^0_s$ and $\Lambda$ particles emitted in 7 TeV pp collisions are presented using the CMS detector. With the implementation of a high-multiplicity trigger during the 2010 LHC pp run, CMS is capable of probing the most exotic high multiplicity pp collisions. The second-order ($v_2$) and third-order ($v_3$) anisotropy harmonics of charged particles, $K^0_s$ and $\Lambda$ particles are extracted from long-range correlations as a function of particle multiplicity and $p_T$, after correcting for the contribution of back-to-back jet correlations. Four-particle cumulants ($c_2${4}) are also measured for charged particles as a function of multiplicity. The results are compared to 5.02 TeV pPb data covering a similar range of particle multiplicity. These new studies will provide stringent constraints on the possible origin of long-range correlations observed in small collision systems.

Speaker: Zhenyu Chen (Rice University (US))

QM15_Zhenyu_v6.pdf

3:20 PM Strangeness production as a function of charged particle multiplicity in proton-proton collisions

Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. These observations warrant a comprehensive measurement of the production of identified particles. We report on the production of $K_{\rm S}^{0},~\Lambda,~\bar\Lambda$, $\Xi^{-}$, $\bar\Xi^{+}$, $\Omega^{-}$ and $\bar\Omega^{+}$ at mid-rapidity measured as a function of multiplicity in pp collisions at $\sqrt{s}$ = 7 TeV with the ALICE experiment. Spectral shapes studied both for individual particles and via particle ratios such as ($\Lambda/K_{\rm S}^{0}$) as a function of $p_{\rm T}$ exhibit an evolution with event multiplicity and the production rates of hyperons are observed to increase more strongly than those of non-strange hadrons. These phenomena are qualitatively similar to the ones observed in p-Pb and Pb-Pb collisions.

Speaker: Livio Bianchi (University of Houston (US))

LivioBianchi_QM2015_v6.pdf

3:40 PM Causal hydrodynamic fluctuation in Bjorken expansion

We investigate effects of causal hydrodynamic fluctuation on dynamics of the quark gluon plasma (QGP) in Bjorken expansion in high-energy nuclear collisions. The space-time evolution of the QGP can be well described by relativistic hydrodynamics. In the recent hydrodynamic analyses, effects of event-by-event (e-by-e) initial fluctuation on final flow observables have been focused. Moreover, it is hotly debated whether the same hydrodynamic models can be applicable even in small systems such as p-p, p-A, and peripheral A-A collisions. In this study, we focus on thermal fluctuation during hydrodynamic evolution which must be also important on an e-by-e basis of hydrodynamic description, in particular, in small systems. We first introduce causal hydrodynamic fluctuation, namely the thermal noises arising during the hydrodynamic evolution, into the boost invariant Bjorken expansion. We next perform hydrodynamic simulations of the Bjorken model with hydrodynamic fluctuation on an e-by-e basis. We find the final entropy fluctuates around the mean value even if the initial condition is fixed in a macroscopic sense. We also find the entropy can temporally decreases during the time evolution, which is allowed by the fluctuation theorem in non-equilibrium statistical physics. Fluctuation of entropy results in multiplicity fluctuation as an observable. Through the fluctuation-dissipation relation, hydrodynamic fluctuation is intimately related with dissipation. Thus final multiplicity fluctuation contains transport properties of the QGP. The fluctuation effect would be significant in small system such as p-p, p-A and peripheral A-A collisions. Therefore we may have a chance to constrain the transport properties in such small systems. We further discuss rapidity　dependent hydrodynamic fluctuation on top of boost-invariant Bjorken expansion to see whether long-range rapidity correlation can be contaminated by hydrodynamic fluctuations.

Speaker: Kenichi Nagai (Sophia university)

Causal hydrodynamic fluctuation3.pdf

Causal hydrodynamic fluctuation3.pptx

4:00 PM Saturation or collectivity in p+A collisions at RHIC and LHC?

I will discuss recent experimental results in proton-proton, proton-lead and deuteron-gold collisions at the LHC and RHIC, and explain how they influence our understanding of non-perturbative QCD at high energy density. Several ideas that may help to disentangle between initial state effects, e.g., the color glass condensate, and final state effects such as hydrodynamics or transport models will be presented. In particular I will discuss the measurement of mean multiplicity vs the number of participants in p+A, the average transverse momentum of produced particles and the elliptic flow as a function of rapidity in p+A, and relations between two-, four-, six- and eight-particle azimuthal anisotropies in p+A and A+A interactions.

Speaker: Adam Bzdak (AGH University of Science and Technology)

bzdak_qm15.pdf

2:00 PM → 4:20 PM Future Experimental Facilities, Upgrades, and Instrumentation

Convener: Megumi Naruki (Kyoto Univ. (JP))

2:00 PM Prospects for the dense baryonic matter research at NICA

The NICA (Nuclotron-based Ion Collider fAcility) project is under preparation at the Joint Institute for Nuclear Research (JINR, Dubna). The main goal of the project is a study of hot and dense strongly interacting matter in heavy ion collisions (up to gold) in the energy range up to √s_NN = 11 GeV. Two modes of operation are foreseen, collider and extracted beams, with two detectors: MPD and BM@N. In the collider mode the designed average luminosity is 10E27 cm-2 s-1 for Au(79+). The proposed experimental program allows one to search for manifestations of the phase transitions and critical phenomena.

Speaker: Prof. Vladimir Kekelidze (Joint Inst. for Nuclear Research (RU))

KekelidzeV.pdf

KekelidzeV.pptx

2:20 PM Studies of high density baryon matter with high intensity heavy-ion beams at J-PARC

We are developing a future heavy-ion program at J-PARC, which is one of the world’s highest intensity proton synchrotrons. In heavy-ion collisions at J-PARC, matter whose density is 8-10 times as high as the normal nuclear density, comparable to that of the neutron star core will be created. There, we aim at exploring QCD phase structures such as the critical point and phase boundaries, and studying modifications of the strong interaction at high baryon density through the investigation of hadron properties and production of exotic hadrons and nuclei. Ions up to U will be accelerated to 1-19 AGeV ($\sqrt{s_{NN}}=2-6.2$ GeV) at the beam rate up to $10^{11}$ ions per cycle of Main Ring synchrotron (MR). We have designed a heavy-ion acceleration scheme with a new linac and a booster as the injector, combined with the existing 3-GeV Rapid-Cycling Synchrotron (RCS) and 50-GeV MR that have been proven to accelerate high-rate proton beams. In heavy-ion experiments, we will measure electrons and muons to study the chiral restoration of vector mesons, and the event-by-event fluctuations of conserved charges to search for the critical point in addition to the conventional systematic studies of various hadrons in the wide energy range. We will also measure particle correlations to study the properties of particle interactions. Last but not least, we will also search for exotic hadrons and nuclei such as dibaryons, kaonic nuclei, and measure hypernuclei at high density, which is one of the important topics in hadron physics. We are designing a large acceptance heavy-ion spectrometer based on a Toroidal magnet to measure hadrons, lepton pairs, and event-by-event fluctuations. We are also designing a closed geometry spectrometer to measure hypernuclei to study weak decays and magnetic moments. In this presentation, the preliminary version of the designed acceleration scheme, as well as the spectrometers and their expected performance and physics results are presented.

Speaker: Dr Hiroyuki Sako (ASRC/J-PARC, Japan Atomic Energy Agency)

QM15-JPARCHI.pdf

QM15-JPARCHI.pdf

QM15-JPARCHI.pdf

QM15-JPARCHI.pptx

QM15-JPARCHI.pptx

QM15-JPARCHI.pptx

2:40 PM Nuclear collisions at the Future Circular Collider

The Future Circular Collider (FCC) is the project for an electron and hadron collider in a new 80-100 km tunnel in the Geneva area. In hadron mode, a centre-of-mass energy of order 100 TeV would be achieved in pp collisions. A design study is under development to be concluded in 2018, with the target start of operation of the machine in 2035-40. The FCC could operate with heavy ions, providing Pb-Pb and p-Pb collisions at centre-of-mass energies of 39 and 63 TeV, respectively, with monthly integrated luminosities of order 5-10/nb. We will present the updated studies on the physics opportunities with heavy ions at the FCC, emphasising the new developments since last Quark Matter, on four topics: bulk observables with focus on the new degrees of freedom (charm) that can be active; hard probes that are produced more abundantly than at the LHC and offer possibilities for new kinds of studies through boosted heavy objects (such as top quarks) or for quarkonia; small-x studies in p-Pb with the large enlargement of the kinematic x-Q^2 plane that the huge collision energy implies; and ultra-peripheral collisions where small-x and electro-weak studies can be performed. Implications on other fields like the physics of very high-energy cosmic rays, will also be presented.

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

armesto-FCCAA-qm2015_1509.pdf

3:00 PM The STAR Heavy Flavor Tracker and Upgrade Plan

The Heavy Flavor Tracker (HFT) of the STAR experiment at RHIC is the first application of the state-of-the-art thin Monolithic Active Pixel Sensors (MAPS) technology in a collider environment. The HFT, composed of two silicon PiXeL detector (PXL) layers, an Intermediate Silicon Tracker (IST) and a Silicon Strip Detector (SSD), greatly improves the impact parameter resolution of STAR tracking and enables reconstruction of hadronic decays of heavy flavor mesons and baryons in the heavy ion collision environment, providing unique probes for studying the Quark-Gluon Plasma. In this talk we will discuss the HFT hardware design, and current detector status and performance. The HFT was successfully commissioned during the 2014 RHIC run, taking data in Au+Au collisions at 200 GeV. The HFT performance during this run matches the expected performance, most significantly for track pointing resolution. We will show preliminary results from 2014 Au+Au data analyses, demonstrating the capabilities of charm reconstruction with the HFT. We will also describe recent modifications to HFT subsystems to improve its reliability, material budget, and tracking in the 2015 run, when the HFT has been taking data in p+p, p+Au and p+Al collisions at $\sqrt{s_{NN}}=$200 GeV. In order to extend these capabilities of measuring bottom quark hadrons at RHIC energies, a faster heavy flavor tracker (HFT+) is needed to collect data at higher luminosity with good efficiency. The proposed HFT+ will be equipped with new generation of MAPS sensors with a much shorter integration time (≤ 20 μs) and possibly extend the current PXL detector acceptance with minimal modification to the original mechanical and air cooling infrastructure. Requirements for the upgraded HFT+ detector and expected performance will be also presented in this talk.

Speaker: Giacomo Contin (Lawrence Berkeley National Lab. (US))

HFT_QM_GContin.pdf

3:20 PM sPHENIX calorimeter design and jet performance

The PHENIX collaboration is planning a major detector upgrade, sPHENIX, consisting of large acceptance calorimetry and precision tracking in conjunction with the recently acquired BaBar 1.5~T superconducting solenoid. The sPHENIX calorimeter system consists of an inner layer of tungsten-scintillating fiber electromagnetic calorimeter surrounded by two layers of sampling hadronic calorimeters made of scintillator tiles and metal plates. The calorimeters provide full azimuthal coverage for $|\eta|<1$ for calorimetry-based jet measurements and low bias jet triggering, enabling a very rich jet physics program at RHIC. We present the current state of the sPHENIX calorimeter design along with studies of their expected performance for jet measurements.

Speaker: John Haggerty (Brookhaven National Laboratory)

sphenix_haggerty_qm2015_submit.pdf

3:40 PM Upgrade of the ALICE Inner Tracking System

During the long shutdown of the LHC in 2018/19 (LS2) the present Inner Tracking System (ITS) of the ALICE experiment based on silicon pixel, silicon drift and silicon strip detectors, will be entirely replaced by a new tracker using novel monolithic silicon pixel chips. This new tracker will significantly enhance heavy flavor measurements, which are out of reach for the present system, e.g. charmed baryons, such as the ΛC, and will allow studying hadrons containing a beauty quark. The new tracker will provide an improved pointing resolution in r-­‐ φ and z, decreasing the present values by a factor 3 and 5, respectively, to about 40 microns for a pT of 500 MeV/c. Each of the seven layers will be constructed using 50 micron thin silicon chips on a very light weight carbon fiber based support structure, allowing to achieve a very low material budget for the first three layers of 0.3% X0/layer and 0.8% X0/layer for the four outer layers. The innermost layer will be placed at 23 mm radius, compared to presently 39 mm. Furthermore, the readout rate of the new ITS will increase from presently 1kHz to 50 kHz for Pb-­‐Pb collisions and 400 kHz for p-­‐p collisions, thus matching the expected event rate for Pb-­‐Pb collisions after LS2. This presentation will provide an overview of the upgrade of the ALICE ITS and the expected performance improvement. It will present the actual status of the R&D and give an outlook on the construction phase starting in 2016.

Speaker: Petra Riedler (CERN)

qm_priedler_itsupgrade_25092015.pdf

4:00 PM The ALICE TPC: from wires to GEMs

The ALICE Time Projection Chamber, the largest of its kind, has been operated during the LHC RUN 1 and is being operated during RUN 2, with Multi-Wire Proportional readout Chambers. These chambers feature a Gating Grid which is pulsed at a maximum frequency of about 3 kHz and allows one to amplify the charge produced in triggered events and prevents ions to invade the drift region, such that space-charge distortions are minimized. Analysis of data from LHC Run1 and first look at data from Run2 had demonstrated excellent performance both for particle identification via dE/dx and tracking. A summary of the performance will be presented. For RUN 3 and RUN 4, where collision rates of 50 kHz are expected, our aim is to preserve this excellent performance while removing the inherent rate limitation imposed by the gating grid, such that 50 kHz read-out rate can be achieved. To this end, a new concept for continuous readout at a minimum of space-charge build-up in the drift volume will be adopted. A novel configuration of GEM detectors has been developed that allows one to maintain excellent particle identification and effective ion trapping, by stacking four GEM foils with different hole pitches and operated under an ad hoc field configuration. Results of intensive R&D to achieve this goal will be summarized, including the demonstration of robustness against discharges. We will also discuss the detector production phase, which is just starting, and includes extensive and repeated quality assurance to ensure the reliability of the chambers once they are installed in the TPC.

Speaker: Chilo Garabatos Cuadrado (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

TPCU_Garabatos_QM2015_Final_1.pdf

TPCU_Garabatos_QM2015_Final.pdf

4:20 PM → 4:30 PM Short Break

4:30 PM → 6:30 PM Poster Session

4:30 PM "NA61/SHINE results on spectra and yields in p+p and Be+Be collisions at CERN SPS energies"

The signatures of the onset of deconfinement were reported by the NA49 experiment in the energy scan of central Pb+Pb collisions. This motivated the strong interactions program of the NA61/SHINE experiment, where possible evidences of the energy threshold for deconfinement will be searched in proton+proton, proton+nucleus, and nucleus+nucleus interactions. In this contribution intriguing results will be presented based on NA61/SHINE spectra and yields of identified hadrons obtained in inelastic p+p interactions and centrality selected Be+Be collisions at CERN SPS energies. The NA61/SHINE results will be compared with NA49 ones as well as with model predictions.

Speaker: Katarzyna Grebieszkow (Warsaw University of Technology (PL))

4:30 PM "QCD equation of state at finite density and finite magnetic field"

The Polyakov linear-sigma model (PLSM) and Hadron Resonance Gas (HRG) model are considered to study the hadronic and partonic equation(s) of state for the case of nonzero external magnetic fields. Thermodynamic quantities including the pressure, interaction rate, entropy density, magnetization and the speed of sound are presented as function of the temperature and the magnetic field and compared with recent lattice QCD calculations. Positive magnetization indicates paramagnetic properties. Direct and inverse catalysis depends on increasing and decreasing critical temperature with the magnetic field. Confronting PLSM and HRG to lattice QCD gives an indirect estimation for the effective degrees of freedom, coupling, etc.

Speaker: Ms nada ezzelarab (Researcher and teaching assistant at MTI univ.)

4:30 PM $\Lambda$ and $K^{0}_{s}$ production in Au+Au collisions at $1.23$ AGeV with the HADES experiment

Over the years an extensive amount of data in the $1$-$2$ AGeV energy regime has been collected leading to enormous improvements of our understanding of particle production mechanisms and HIC dynamics. At these beam energies the production of hadrons is observed below or slightly above their free elementary production threshold. Due to this fact a comparison to reference data from elementary collisions is not straightforward and phenomenological models are mandatory. For this analysis, $7.3$ billion of the 40$\%$ most central Au($1.23$ AGeV per nucleon)+Au reactions have been used to reconstruct the weakly decaying strange hadrons $K^{0}_{s}$ and $\Lambda$. In order to draw conclusions on strangeness production mechanisms the yields will be compared to non-strange particle production and phenomenological models, allowing to further deepen our understanding of hadron production in HIC. Supported by BMBF (05P12RFGHJ), HIC for FAIR, GSI, HGS-HIRe and H-QM.

Speaker: Mr Timo Scheib (Goethe University)

QM2015_Poster_TScheib.pdf

4:30 PM $\Lambda-\Lambda$ Correlation in High Energy Heavy Ion Collisions

We show that $\Lambda\Lambda$ intensity correlation function $C(Q=k_1-k_2)$ measured in high energy heavy ion collisions can constrain the interaction between two $\Lambda$ [1]. For various $\Lambda\Lambda$ interaction potentials in literature, summarized in the figure with corresponding low energy scattering parameters, we compute the $\Lambda\Lambda$ relative wave function $\Psi(x_1,x_2;Q)$ by assuming modification of the wave function in $S-$wave and discuss the relation between the scattering parameters and the behavior of the correlation function $ C(Q,K) = \frac{\int dx_1 \int dx_2 S(x_1,K)S(x_2,K)|\Psi(x_1,x_2;Q)|^2}{\int dx_1 S(x_1,k_1) \int dx_2 S(x_2,k_2)}, $ where $S(x,K)$ denote the source function which is the phase space distribution of $\Lambda$ at freeze-out. Employing a Gaussian source model with longitudinal and transverse expansion as a source function of $\Lambda$, we discuss the parameter ranges of the scattering length $a_0$ and the effective range $r_{\text{eff}}$ constrained from experimental data in Au+Au collisions at $\sqrt{s_{NN}}=200$GeV measured by the STAR collaboration [2]. The contribution from electromagnetic decay $\Sigma^0 \rightarrow \Lambda \gamma$ is found to be important. We also point out the existence of residual correlation in the high $Q$ region which cannot be explained in the present framework. Consequently, we obtained a constraint on the scattering length $1/a_0 < -0.8 \text{fm}^{-1}$. We will also address an application of this method to other systems, such as $\Omega-N$ [3]. 1. K.Morita, T.Furumoto, A.Ohnishi, Phys. Rev. C **91**, 024916 (2015). 2. L.Adamczyk et al. (STAR Collaboration), Phys. Rev. Lett. **114**, 022301 (2015). 3. K.Morita, A.Ohnishi, T.Hatsuda, work in progress. ![$\Lambda\Lambda$ scattering parameters][4] [4]: http://www2.yukawa.kyoto-u.ac.jp/~kenji.morita/LL2.jpg

Speaker: Kenji Morita (Kyoto University)

LL.pdf

4:30 PM $\Lambda_\mathrm{c}^+$ baryon production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV

Baryon/meson ratios (p/$\pi$, $\Lambda$/K$^0_\mathrm{s}$) are observed to be significantly enhanced in central heavy-ion collisions compared with peripheral heavy-ion collisions and p+p collisions at RHIC and LHC. Several model calculations suggest that coalescence hadronization between charm quarks and light quarks will also lead to an enhancement in the $\Lambda_\mathrm{c}$/D$^0$ ratio. Therefore, it is of great interest to study the $\Lambda_\mathrm{c}$ baryon production to further understand the hadronization scheme in the charm sector and constrain total charm yield in heavy-ion collisions. The possible $\Lambda_\mathrm{c}$/D$^0$ enhancement in heavy-ion collisions will introduce additional suppression for charm decay electrons due to smaller semi-leptonic decay branching ratios of $\Lambda_\mathrm{c}$, which could lead to a different interpretation of the heavy flavor decay electron results. $\Lambda_\mathrm{c}$ baryons have an extremely small lifetime ($c \tau \sim 60$ $\mu$m) and have not been measured in heavy-ion collisions yet. The newly installed STAR Heavy Flavor Tracker (HFT) has shown high efficiency and a superior pointing resolution that facilitate the reconstruction of hadronic decays in heavy-ion collisions. In 2014 run, STAR has collected 1.2 B events of minimum bias Au+Au collisions $\sqrt{s_\mathrm{NN}}$ = 200 GeV. In this poster, we will discuss the feasibility of $\Lambda_\mathrm{c}$ measurement with the HFT in Au+Au collisions. We will report reconstruction of $\Lambda_\mathrm{c}$ baryons via hadronic decays, including decay channels through the involvement of various intermediate resonance states using 2014 Au+Au data at $\sqrt{s_\mathrm{NN}}$ = 200 GeV. In addition, we will discuss the improvement on $\Lambda_\mathrm{c}$ reconstruction using the HFT with reduced material that is taking data in 2015 (p+p, p+A) and is planned for future 2016 (Au+Au) collisions.

Speaker: Miroslav Simko (Nuclear Physics Institute of the CAS (CZ))

QM15poster_Lc_v9.pdf

4:30 PM $\Omega-N$ Interaction from Relativistic Heavy Ion Collisions

We investigate the two-particle momentum intensity correlation function for $\Omega N$ pairs $ C(Q,K) = \frac{\int dx_1 \int dx_2 S_\Omega(x_1,K)S_N(x_2,K)|\Psi(x_1,x_2;Q)|^2}{\int dx_1 S_\Omega(x_1,k_1) \int dx_2 S_N(x_2,k_2)} $ where $Q$ is the relative momentum of the two emitted particles and $S_i(x,k)$ denote the source function of particle species $i$. $C(Q,K)$ has been used as a sensitive probe for the source size in nucleus-nucleus collisions, but recently has been investigated for $\Lambda\Lambda$ pairs to probe their interaction [1]. The $N\Omega$ system with $S=-3$ is particularly interesting, since it is one of two multiplets in which the Pauli blocking does not take place thus can form a bound state. Indeed, a recent lattice QCD calculation by the HAL QCD collaboration [2] predicts the existence of $N\Omega$ bound state in the $^5 S_2 (J=2, S=2)$ channel. We adopt the $N\Omega$ interaction potential obtained by the HAL QCD collaboration and calculate the $N\Omega$ correlation function through the relative wave function $\Psi(x_1,x_2;Q)$. Moreover, we also study the variation of the correlation function against the change of the property of the bound state. We show that the correlation function $C(Q)$ is sensitive to whether the system has a bound state or not (see figure). If the system has a bound state, the behavior of $C(Q)$ at low $Q$ also depends on the binding energy. We discuss how the behavior the scattering wave function can influence the behavior of $C(Q)$ and its interplay with the source size. Our result indicates that high energy heavy ion collisions at RHIC and LHC may provide information on the possible existence of the $N\Omega$ dibaryon. 1. K.Morita, T.Furumoto, A.Ohnishi, Phys.Rev.C **91**, 024916 (2015). 2. F.Etiminan et al., (HAL QCD Collaboration), Nucl. Phys. **A928**, 89 (2014). ![Preliminary result][1] [1]: http://www2.yukawa.kyoto-u.ac.jp/~kenji.morita/c2_mix2.jpg

Speaker: Kenji Morita (Kyoto University)

OmegaN.pdf

4:30 PM $\phi$ meson measurement in Cu+Au collisions at $\sqrt{s}_{NN}$ = 200 GeV with the PHENIX Muon Arms at RHIC

A major objective in nuclear physics is to quantify and characterize the hot and dense state of strongly interacting matter formed in high-energy heavy-ion collisions. The $\phi$ meson is an excellent probe for studying this deconfined state of nuclear matter due to its very short lifetime, and the absence of strong interactions between muons and the surrounding hot hadronic matter makes the $\phi$ to dimuon decay channel particularly interesting. Since the $\phi$ meson is composed of a strange and antistrange quark, its nuclear modification in heavy-ion collisions can be used to study strangeness enhancement in-medium. Additionally, the rapidity dependence of $\phi$ production in asymmetric heavy-ion collisions provides a unique means of accessing different mixtures of initial and final state effects. In this poster, we present the measurement of $\phi$ meson production and nuclear modification in asymmetric Cu+Au heavy-ion collisions at $\sqrt{s}_{NN}$ = 200 GeV at both forward (Cu-going direction) and backward (Au-going direction) rapidities.

Speaker: Prof. Xiaochun He (Georgia State University)

QM15_Poster_Jezghani_v3.pdf

4:30 PM $\phi$ production in $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the PHENIX detector at RHIC

The $\phi$ production in high-energy heavy-ion collisions provides key information on the hot and dense state of the strongly interacting matter produced in such collisions. They are sensitive to the medium-induced effects such as strangeness enhancement, modification of the resonance line shapes and their relative production rates in leptonic and hadronic decay modes linked to the chiral symmetry restoration. Measurements in the dilepton channels are especially interesting since leptons interact only electromagnetically, thus carrying the information from their production phase directly to the detector. Measurements of $\phi$ production in $^3$He+Au collisions, a new collision system, add to the existing results ($p$+$p$, $d$+Au and Cu+Au) which extends our ability to have a systematic study of nuclear medium effects on $\phi$ production. The PHENIX detector provides the capabilities to measure the $\phi$ production in a wide range of transverse momentum and rapidity to study various cold nuclear effects such as soft multiple parton rescattering and modification of the parton distribution functions in nuclei. In this poster, we report the current status of the $\phi$ meson production measurement from $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.

Speaker: Murad Sarsour (Georgia State University)

4:30 PM $\rm{D^+}$-meson nuclear modification factor in Pb--Pb collisions with ALICE

Heavy quarks (charm and beauty) can be used to study the properties of the strongly-interacting matter that is created in central Pb--Pb collisions at ultrarelativistic energies. They are produced in parton scattering processes with high-momentum transfer in the initial stages of the collisions. Therefore, the heavy quarks experience all the phases of the system evolution losing energy in the medium via gluon radiation and elastic collisions. The measurement of the D-meson nuclear modification factor ($R_{\rm AA}$) is sensitive to the in-medium energy loss of charm quarks. The D-meson production has been studied by ALICE in pp, p--Pb and Pb--Pb collisions. In particular, the measurement of the $\rm D^+$-meson nuclear modification factor in Pb--Pb collisions at $\sqrt {s_{\rm NN}} = 2.76$ TeV, collected in 2011, will be presented. The dependence of the $\rm D^+$-meson $R_{\rm AA}$ on its transverse momentum and on the centrality of the collisions will be reported.

Speaker: Cristina Bedda (Universita e INFN Torino (IT))

POSTER_QM_Bedda.pdf

4:30 PM $\Upsilon$ measurements in $\mbox{${\it p}+{\it p}$}$ collisions at $\mbox{$\sqrt{s}=500\:\mathrm{GeV}$}$ with the STAR experiment

Studies of quarkonium production in heavy-ion collisions can provide insight into thermodynamic properties of the quark-gluon plasma (QGP). Suppression of $\Upsilon$ states is expected at a sufficiently high temperature in the QGP and can be measured using the nuclear modification factor $\mbox{$R_{\textit{AA}}$}$. Measurements of $p_{T}$ spectra for separate $\Upsilon$ states in $\mbox{${\it p}+{\it p}$}$ collisions provide constraints for models of the quarkonium production, which is an important factor in the interpretation of the heavy-ion results. In addition, high quality data from $\mbox{${\it p}+{\it p}$}$ collisions at $\mbox{$\sqrt{s}=500\:\mathrm{GeV}$}$ can be used as a baseline for $\mbox{$R_{\textit{AA}}$}$ as a function of $p_{T}$ in $\mbox{${\it Au}+{\it Au}$}$ collisions at $\mbox{$\sqrt{s}=200\:\mathrm{GeV}$}$, after rescaling to lower energy. Also, studies of ratios of $\Upsilon$ states as a function of event multiplicity may help better understand the interactions with hadronic co-movers, because the higher states have larger geometrical sizes and thus should have larger cross section for such interactions compared to $\Upsilon(1S)$. In this poster, we will focus on experimental aspects and report the preliminary results of $\Upsilon$ measurements in $\mbox{${\it p}+{\it p}$}$ collisions at $\mbox{$\sqrt{s}=500\:\mathrm{GeV}$}$ with the STAR experiment. Furthermore, the prospects of $\Upsilon$ measurements with the newly installed Muon Telescope Detector (MTD) will be discussed.

Speaker: Leszek Kosarzewski (Warsaw University of Technology)

QM15_Upsilon_poster_LK_v3.pdf

4:30 PM $D_{s}^{\pm}$ meson production in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV in STAR

Heavy quarks, produced in hard scattering processes in the initial stages of the collisions, are considered as excellent probes for the strongly interacting deconfined medium formed in heavy-ion collisions. The $D_{s}($c$\bar{s}/\bar{c}$s)production is affected by the strangeness enhancement and the primordial charm quark production. Thus the modification of the $D_{s}$ meson spectra in ultra-relativistic heavy-ion collisions provides a new interesting probe to the key properties of the hot nuclear medium. The Heavy Flavor Tracker, installed in STAR in 2014, has been designed to extend STAR’s capability of measuring heavy flavor production by the topological reconstruction of displaced decay vertices. It provides a unique opportunity for precise measurement of the $D_{s}$ meson production. We will present the first measurement of $D_{s}$ meson production via two decay channels $D_{s}\rightarrow\phi(1020)+\pi$, and $D_{s}\rightarrow$$K+K^{\star}$(892) in Au+Au collisions at 200GeV. Preliminary results on the central-to-peripheral nuclear modification factor ($R_{cp}$) will also be presented.

Speaker: Long Zhou (USTC && BNL)

QM15poster_LongZhou_V6.pdf

4:30 PM $K^{*}(892)^{0}$ production at high transverse momentum in pp and Pb–Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

The ALICE experiment has unique particle-identification capabilities allowing one to identify pions, kaons and protons over a wide momentum range through the measurements of their specific energy loss in the Time Projection Chamber (TPC) and of their velocity in the Time-Of-Flight (TOF) detector. Hadronic resonances can therefore be successfully reconstructed via invariant mass analysis of the daughter particles in the hadronic decay channels. The measurement of the production of the $K^{\star}(892)^{0}$ resonance in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV and pp collisions at $\sqrt{s}$ = 2.76 TeV is reported. The yield of $K^{\star}(892)^{0}$ at high $p_{\rm T}$ is observed to be suppressed in Pb-Pb relative to pp collisions due to the effect of parton energy loss in the hot and dense medium created in nuclear collisions. This has been studied via the measurement of the $K^{\star}(892)^{0}$ nuclear modification factor ($R_{AA}$). Further understanding on the particle production mechanism can be provided by the measurement of the particle ratios $K^{\star}$/K and $\phi$/K over a wide transverse momentum ($p_{T}$) range.

Speaker: Kishora Nayak (National Institute of Science Education and Research (IN))

4:30 PM ${\rm D}^{\star +}$-meson production in p--Pb collisions in ALICE

Heavy quarks (charm and beauty) are effective probes to investigate the properties of the Quark-Gluon Plasma created in high-energy heavy-ion collisions at the LHC. They are primarily produced in hard scattering processes in the early stage of the collision, after which they experience the full evolution of the system. Previous measurements have shown that the production of prompt D mesons in central Pb--Pb collisions is strongly suppressed in comparison to binary-scaled pp collisions. This suppression may be interpreted as an energy loss of the heavy quarks in the hot and dense medium due to collisional and radiative processes. To obtain a more complete picture on the Pb--Pb results, an understanding of cold nuclear matter effects in the initial and final state such as modification of parton densities in nuclei, $k_{\rm T}$ broadening and energy loss in cold nuclear matter, is required. These effects are accessible in p--Pb collisions. Here, the measurement of prompt ${\rm D}^{\star +}$ production in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector will be presented.

Speaker: Jasper Van Der Maarel (Nikhef National institute for subatomic physics (NL))

QM poster v6.pdf

4:30 PM (Anti-)strangeness production in heavy-ion collisions

We study the production of (anti-) strange and multi-strange hadrons in heavy-ion collisions from FAIR/NICA to LHC energies within the Parton-Hadron-String Dynamics (PHSD) microscopic transport approach, which contains the partonic and hadronic dynamics. By showing the channel decomposition for the strangeness production we demonstrate how with increasing energy the production in the QGP dominates the hadronic production. We observed traces from the QGP by looking at a verity of 'bulk' observables like the excitation functions of particle yields, pt- and rapidity distributions, centrality dependencies of yields, $\langle$ pt $\rangle$ etc. At RHIC energies strange and anti-strange hadrons are produced at mid-rapidity with the same amount, while with decreasing energy the particles dominate more and more over antiparticles.

Speaker: Pierre Moreau (Frankfurt Institute of Advanced Studies)

P.Moreau_QM2015.pdf

4:30 PM (Non-)Critical fluctuation signals and their fate in heavy-ion collisions

A major goal of ongoing experiments in heavy-ion physics is the exploration of the QCD phase diagram with the potential discovery of the QCD critical point. Here, fluctuation observables are considered to be promising quantities for achieving this goal. Present experimental results alone are however inconclusive and need to be accompanied by advanced theoretical calculations which capture the relevant aspects of heavy-ion collisions. In this talk we address two main topics in this context: the dynamical modelling of fluctuations within fluid dynamics and the impact of late stage effects on the (non-)critical signals in the fluctuation observables. In the first part we report on the inclusion of fluctuations into the fluid dynamical evolution equations. We show that (thermal) noise can be consistently incorporated in fluid dynamics and check our results against known equilibrium fluctuations and analytical results for Bjorken flow. This framework also allows one to study the evolution of critical fluctuations, for example by applying transport coefficients with critical behavior or by coupling the sigma-field to a fluid dynamical background. In the second part we assume that critical fluctuations have formed in the collision dynamics according to universality arguments and parametrizations of the correlation length. We study how resonance decay and regeneration as well as the distance of the system's trajectory and the chemical freeze-out from the critical point alter the signals that are expected to be seen in net-proton and net-charge fluctuations.

Speaker: Marcus Bluhm (North Carolina State University)

BluhmQM2015.pdf

4:30 PM A calculation of transport coefficients in 2-nd order hydrodynamics

Based on the Nakajima-Zubarev type non-equilibrium density operator, we derive a 2-nd order hydrodynamic equation. Microscopic Kubo-formulas for all coefficients in the equation are systematically obtained. Coefficients βi and αi in the Israel-Stewart equation are given as current-weighted correlation lengths which are to be calculated in statistical mechanics. We also numerically evaluate the coefficients by using a hadro-molecular simulation and discuss the temperature dependences and the baryon number density dependences.

Speaker: Dr Shin Muroya (Matsumoto University)

4:30 PM A critical reassessment of cold nuclear matter effects in proton-nucleus collisions at RHIC and LHC

Recent results from the p+Pb run at the LHC on light hadron, heavy flavor, and jet production reveal highly non-trivial nuclear cross section modifications, when compared to p+p collisions. These discoveries complement similar earlier findings form d+Au reactions at RHIC. In this talk we present recent calculations and theoretical interpretation for two such examples - the nuclear enhancement for heavy meson production in the backward rapidity region and single inclusive jet production in both d+Au and p+Pb collisions. We demonstrate that the incoherent multiple parton scattering can describe rather well the observed Cronin-like nuclear enhancement in the intermediate pT region of heavy meson production at RHIC and the LHC [1,2]. On the other hand, we show that initial-state inelastic parton processes in p+A collisions lead to attenuation of the jet production cross section, which is amplified at very high pT and forward rapidity. We demonstrate quantitatively to what extent parton energy loss effects in cold nuclear matter can explain the attenuation of the recently observed jet production yields in p(d)+A reactions at RHIC and the LHC [3]. We further show the consistency between the observed scaling behavior of the nuclear modification factor as a function of the jet energy and the initial-state parton energy loss picture. [1]. Z. Kang, I. Vitev and H. Xing, Phys. Rev. D88, 054010. [2]. Z. Kang, I. Vitev, E. Wang, H. Xing and C. Zhang, Phys. Lett. B740, 23. [3]. Z. Kang, I. Vitev and H. Xing, in preparation.

Speaker: Hongxi Xing (LANL)

4:30 PM A Holographic Description of 3-jet Events in Strongly Coupled Plasma

We numerically simulate classical falling string configuration with non-trivial transverse dynamics in thermal AdS_5. These strings develop kink-like structures which, in the dual theory, can be interpreted as the propagation of hard gluons produced in association with a quark anti-quark pair. We observe the appearance of two physically distinct regimes of the in-plasma dynamics depending on whether the medium is able to resolve the transverse structure of the string prior its total quench. From these regimes we extract the transverse resolution scale of the strongly coupled plasma of N=4 SYM and confront it with perturbative results.

Speaker: Andrej Ficnar (Columbia University in the City of New York)

4:30 PM A new cold atom experiment to study the hot quark-gluon plasma

The hot quark-gluon plasma ($\sim 10^{12}$ K) and the cold atom systems ($\sim 10^{-6}$ K) exhibit amazingly similar phenomenon of azimuthal anisotropy [K.M.O’Hara et al., Science 298, 2179 (2002)]. This has been postulated as stemming out of a common underlying mechanism--both systems are strongly interacting and expand hydrodynamically--despite of the very different nature of their interactions. However, recent transport model studies suggest that the anisotropy in heavy-ion collisions may not be dominated by hydrodynamics, but the escape mechanism [L.He et al., arXiv:1502.05572 (2015)]. Moreover, quantum uncertainty principle may be relevant for the anisotropy of the quark-gluon plasma [D.Molnar et al., arXiv:1404.4119 (2014)]. In this talk I will illustrate why the hot quark-gluon plasma and the cold atom experiments performed to date are not similar as have been envisaged, and what it takes to truly use cold atoms to simulate the conditions of the quark-gluon plasma. I will outline a possible future cold atom experiment and discuss the technical challenges of such an experiment as well as the physics opportunities coming with it.

Speaker: Fuqiang Wang (Purdue University (US))

4:30 PM A new Riemann solver for ultrarelativistic nuclear collisions

We present a new shock-capturing numerical scheme for ideal relativistic hydrodynamics based on an exact solution of Riemann problem for an arbitrary equation of state. Having performed standard numerical tests such as sound wave propagation and shock tube problem, we show that the scheme has low numerical viscosity and high precision and thus is particularly suitable for modeling of ultrarelativistic nuclear collisions.

Speaker: Zuzana Feckova

qm2015_feckova.pdf

4:30 PM A small current measurement system for gaseous micropattern detectors suitable for operation at high voltages

Future upgrades of several large particle detectors intend to employ gaseous micropattern detectors. This class of detectors, which include Gas Electron Multipliers (GEMs), Micro-MEsh Gaseous Structure detectors (MicroMegas) and similar, usually require the measurement of small currents (pA) at high potentials (kV) with respect to ground. While only this in itself presents an obstacle, the measurements very often need to satisfy other strict requirements, such as small current resolution, low power consumption, high readout frequencies (1 kHz) or simultaneous readouts of multiple channels. Several instruments that overcome some of these difficulties have been proposed or developed, often lacking in characteristics that would make them universally applicable. We present a description of a high-resolution picoammeter developed in our laboratory. Tests of the prototype with a local Gas Electron Multiplier sheet setup demonstrate that it satisfies all the aforementioned requirements, including a current resolution of less than 15pA, a readout frequency of 1kHz, the ability of simultaneous readout of multiple channels (up to 16) and low battery power consumption. Several prototypes have been sent for independent testing to other institutions, providing feedback for possible improvements, which are either already under way or planned as future upgrades.

Speaker: Nikola Poljak (University of Zagreb (HR))

QM15_NPoljak.pdf

4:30 PM A Spacetime description of Hard Parton evolution in the QGP

Typical energy loss calculations in AdS/CFT simulations use an initial condition of off-shell pairs of quarks placed back-to-back in the QGP, but a precise and theoretically motivated description of this does not exist. Quark virtuality can have noticable effects on the rate of energy loss so a first principals calculation is needed for the early time behaviour of virtual particles soon after production. We use the Schwinger Keldysh formalism to calculate a perturbative expression for the Energy Momentum Tensor of hard partons created before the formation of the Quark Gluon Plasma. We propose this as a foundational model to use in jet energy loss.

Speaker: Ben Meiring (University of Cape Town)

QM2015_Poster.pdf

4:30 PM A Study of Nuclear effects in Drell-Yan and Charmonia Productions in p-A collisions at Fermilab E906/SeaQuest Experiment

Strong suppressions of charmonia have been observed in heavy ion collisions at RHIC and LHC. The suppressions exhibit strong nucleus A and also kinematic dependences, especially with Feynman-x (or rapidity) and transverse momentum pT. Such suppression in heavy ion collisions is predicted to be an important signature for the formation of quark-gluon plasma (QGP) due to color screening, however, there are also other non-QGP effects, such as initial state parton energy loss, parton shadowing and final state breakup, that affect the formation of charmonia. It is important to quantify the contributions from the cold nuclear matter, and it could be achieved through studying charmonia and Drell-Yan productions in proton-nucleus collisions where no significant QGP is expected. E906/SeaQuest is a fixed-target dimuon experiment at Fermilab using the 120 GeV proton beam from the Main Injector. E906 has been taking high statistic data samples of p+p, p+d, p+C, p+Fe and p+W collisions since 2014 and will continue data taking until the summer of 2016. E906 measures J/Psi, Psi’ and Drell-Yan productions in the dimuon channel in p+p and p+A collisions over a wide range of kinematic coverage, that is optimal for the study of the cold nuclear matter effects. Recently, we released the first preliminary measurements of Drell-Yan production in p+A collisions from the 2014 Run-II data. Analyses of J/Psi and Psi’ productions are underway. In this talk, the latest status of the analyses and preliminary results will be presented.

Speaker: Ming Liu (Los Alamos National Laboratory)

4:30 PM A study of vorticity formation in high energy nuclear collisions

We present a quantitative study of vorticity formation in peripheral ultrarelativistic heavy ion collisions at $\sqrt{s_{NN}} = 200$ GeV by using the ECHO-QGP numerical code, implementing relativistic dissipative hydrodynamics in the causal Israel-Stewart framework in 3+1 dimensions with an initial Bjorken flow profile. We consider and discuss different definitions of vorticity which are relevant in relativistic hydrodynamics. After demonstrating the excellent capabilities of our code, which proves to be able to reproduce Gubser flow up to 8 fm/$c$, we show that, with the initial conditions needed to reproduce the measured directed flow in peripheral collisions corresponding to an average impact parameter $b=11.6$ fm and with the Bjorken flow profile for a viscous Quark Gluon Plasma with $\eta/s=0.1$ fixed, a vorticity of the order of some $10^{-2} \; c$/fm can develop at freezeout. The ensuing polarization of $\Lambda$ baryons does not exceed 1.4\% at midrapidity. We show that the amount of developed directed flow is sensitive to both the initial angular momentum of the plasma and its viscosity.

Speaker: Prof. Francesco Becattini (University of Florence (Italy))

poster1.pdf

4:30 PM A Summary Trigger Unit for the ALICE Electromagnetic Calorimeters

After a successful three-year data taking period, the Summary Trigger Unit, a FPGA-based embedded device implementing the ALICE EMCal L1 trigger algorithms, has demonstrated efficient real-time selection of events with high transverse momentum jets and photons. LHC LS1 has been the opportunity for ALICE to upgrade its calorimetry system with DCal, a second arm situated back-to-back in azimuth to EMCal. The exibility and scalability of STU hardware design has then proven to be a major asset to extend its use to both DCal and PHOS calorimeters implementing even more complex L1 Jet Patch algorithms featuring on-line congurable patch sizes, spatial windowing over DCal and PHOS aggregated regions, and dynamic threshold adjustement based on median background estimation through EMCal-DCal custom serial link communication. The poster will present all these new STU developments for the upcoming LHC Run 2.

Speaker: Ritsuya Hosokawa (University of Tsukuba (JP))

4:30 PM A Tungsten Powder Epoxy Scintillating Fiber EMCAL for sPHENIX

The sPHENIX detector is a proposed new detector at the Relativistic Heavy Ion Collider (RHIC). The sPHENIX physics program focuses on jets and hard probes of the quark gluon plasma (QGP). The proposed design of the electromagnetic calorimeter (EMCAL), made of a tungsten powder and epoxy composite with embedded scintillating fibers, is designed to have a small Moliere radius and short radiation length, and will be located at a radius of about 90 cm from the interaction region. It will have an energy resolution $12\%/\sqrt{E}$ and will be used in conjunction with a new hadronic calorimeter (HCAL) to provide a jet energy resolution $\sigma_{E}/E=120\%/\sqrt{E}$ to resolve single photons and electrons, as well as photon jets, in the high multiplicity environment of central heavy ion collisions. The $\eta$ and $\phi$ segmentation of the EMCAL is 0.024 x 0.024. Preliminary tests of the calorimeter design have taken place and we plan to test new prototypes of the EMCAL and HCAL in the spring of 2016 in the test beam at Fermilab.

Speaker: Vera Loggins (University of Illinois Urbana Champaign)

Sphenix_poster_QM2015_revision1.pdf

4:30 PM An Appication of the Non-extensive Phenomena: Soft+Hard Model at Various Energies

Hadron spectra measured in high-energy collisions present distributions which can be derived from the non-extensive statistical and thermodynamical phenomena. Based on earlier theoretical developments, it seems, the methods are very applicable for jets hadronization processes in electron-positron, proton-proton, and even in heavy-ion collisions. Here, we present what can was learnt from the recent theoretical and phenomenological developments: transverse momentum spectra and azimuthal anisotropy (v2) of charge averaged pions, kaons and protons stemming from high-energy collisions form RHIC to LHC energies, which are described analytically in a ‘soft + hard’ model. In this model, we propose that hadron yields produced in heavy-ion collisions are simply the sum of yields stemming from jets (hard yields) in addition to the yields originating from the Quark-Gluon Plasma (soft yields). The hadron spectra in both types of yields are approximated by the Tsallis – Pareto like distribution

Speaker: Gergely Barnafoldi (Hungarian Academy of Sciences (HU))

BarnafoldiGG_QM2015_v3.pdf

4:30 PM An evidence for the hadron-­quark-­gluon mixed phase formation in nuclear collisions

With the help of an advanced version of the hadron resonance gas
model we have found remarkable irregularities of relativistic heavy­ ion
collisions at chemical freeze­-out. They include an abrupt change of the
effective number of degrees of freedom at laboratory energies 8.9­-11.6
AGeV and plateaus in the collision­ energy dependence of the entropy per
baryon, pion number per baryon, and a sharp peak in the dimensionless trace anomaly at at chemical freeze-out laboratory energy 11.6 AGeV [1,2]. On the basis of the generalized shock-adiabat model we demonstrate that these observations give evidence for the anomalous thermodynamic properties of the mixed phase at its boundary to the QGP [2]. We argue that the trace anomaly peak and the local minimum of the generalized specific volume observed
at a laboratory energy of 11.6 AGeV provide a signal for the formation of
a mixed phase between the QGP and the hadron phase. This is also supported by an independent meta-analysis [3]: we compare the quality of hadron spectra and multiplicities description from 10 different models in the range of $\sqrt{s_{NN}}$ from 2.1 GeV to 17.3 GeV and find that at 5-10.8 GeV and above 12 GeV models assuming QGP perform notably better, while at 4.4­-4.87 GeV and 10.8­-12 GeV QGP models perform as good as purely hadron ones.

Based on these findings, the practical suggestions for the collision energies of the future
experiments on RHIC, NICA and FAIR are formulated.

1. K. A. Bugaev, A. I. Ivanytskyi, et al
Thermodynamically Anomalous Regions As A Mixed Phase Signal, Phys.
Part. Nucl. Lett. 12, 238­245 (2015).

2. K. A. Bugaev, A. I. Ivanytskyi, et al
Thermodynamically Anomalous Regions and Possible New Signals of
Mixed Phase Formation, arXiv:1412.0718 [nucl­-th].

3. V. A. Kizka, V. S. Trubnikov, K. A. Bugaev and D. R. Oliinychenko, A
possible evidence of the hadron­-quark­-gluon mixed phase formation in
nuclear collisions, arXiv:1504.06483 [hep­-ph].

Speaker: Dmytro Oliinychenko (FIAS, Goethe University, Ruth­Moufang Str. 1, 60438 Frankfurt upon Main, Bogolyubov Institute for Theoretical Physics of the National Academy of Germany, Sciences of Ukraine, 03680, Kiev, Ukraine)

Oliinychenko_Bugaev_QM15.pdf

4:30 PM Analysis methods to extract possible flow and ridge signal in small systems and application to high multiplicity events in 510 GeV p+p collisions at RHIC PHENIX experiment

Elliptic flow and ridge-like correlation have been observed in heavy-ion collision and they are considered as important probes for understanding the hydrodynamic properties of Quark Gluon Plasma. The ridge and $v_{2}$ are also measured in $d+Au$ and $^{3}He+Au$ collisions at RHIC, and in $p+p$ and $p+Pb$ collisions at LHC, therefore these observation have raised a great interest whether a similar hot and dense matter observed in heavy ion collision is also formed in small systems or not. 510 GeV p+p collisions were operated at RHIC in 2013. So far in p+p collisions at 200 GeV, ridge-like signal have not been found yet. However, there is significant difference in the multiplicity between 510 GeV and 200 GeV, so comparison of the two energies could provide an important insight on multiplicity and collision energy dependent studies with small collision systems. In this poster, we report current status of flow and long-range correlation studies in high-multiplicity $p+p$ collisions at $\sqrt{s_{NN}}=510$ GeV with various analysis methods including (1) 2-particle correlation, (2) event plane as well as (3) reference fitting methods, and possibly to compare with $p+p$ collisions at $\sqrt{s_{NN}}=200$ GeV and other small collision systems, such as $p+A$, $d+A$ and $^{3}He+A$ collisions at RHIC energies in PHENIX experiment.

Speaker: Yusuke Fukuda (University of Tsukuba (JP))

QM15poster_yusuke_ver3.pdf

4:30 PM Analysis of charmonium at finite temperature from complex Borel sum rules

Recently, we proposed a new type of QCD sum rules i.e. the complex Borel sum rules (CBSR) [1]. It has been found that the CBSR is superior to the conventional QCD sum rules from the point of view of the maximum entropy method (MEM) analysis. Specifically, we have demonstrated that our novel method can be used to study the excited states of hadrons. The suppression of quarkonium states (e.g. J/psi and upsilon) is an important signature of the hot matter produced in relativistic heavy-ion collisions at RHIC and LHC. Recently, the behavior of the excited states at finite temperature, which can be different from the ground state, has attracted much attention. The suppression of the quarkonium ground states has already been analyzed by conventional QCD sum rules with MEM [2,3]. In this presentation, we report on the results of a reanalysis by CBSR with MEM to investigate the thermal behavior of the charmonium excited states. [1] K.J. Araki, K. Ohtani, P. Gubler and M. Oka, Prog. Theor. Exp. Phys. 2014 073B03 (2014) [2] P. Gubler, K. Morita, and M. Oka, Phys. Rev. Lett. 107, 092003 (2011). [3] K. Suzuki, P. Gubler, K. Morita, and M. Oka, Nucl. Phys. A 897, 28 (2013).

Speaker: Kenji Araki (Tokyo Institute of Technology)

QM2015 ポスター.pdf

4:30 PM Analytical and numerical Gubser solutions of the second-order hydrodynamics

Evolution of quark-gluon plasma (QGP) near equilibrium can be described by the second-order relativistic viscous hydrodynamic equations. Consistent and analytically verifiable numerical solutions are critical for phenomenological studies of the collective behavior of QGP in high-energy heavy-ion collisions. A novel analytical solution based on the conformal Gubser flow which is a boost-invariant solution with transverse fluid velocity is presented. Due to the non-linear nature of the equation, the analytical solution is non-perturbative and exhibits features that are rather distinct from solutions to usual linear hydrodynamic equations. It is used to verify with high precision the numerical solution with a newly developed state-of-the-art (3+1)-dimensional second-order viscous hydro code (CLVisc). The perfect agreement between the analytical and numerical solutions demonstrates the reliability of the numerical simulations with the second-order viscous corrections. This lays the foundation for future phenomenological studies that allow one to gain access to the second-order transport coefficients.

Speaker: Bowen Xiao (Central China Normal University)

4:30 PM Analytical solution of the nonlinear relativistic Boltzmann equation in the early universe and the thermalization of expanding systems

In this talk we present a general method for computing exactly the nonlinear collision term of the relativistic Boltzmann equation for a homogeneous and isotropic system [1]. This is used to find the first full analytical solution of the nonlinear Boltzmann equation for an expanding system corresponding to the primordial matter in the early universe. This solution is used to investigate (in an analytical manner) how thermalization is reached in rapidly expanding kinetic systems. We also determine whether this expanding system displays a nontrivial scaling solution corresponding to a nonthermal fixed point. Reference: [1] D. Bazow, G. S. Denicol, U. Heinz, M. Martinez, and J. Noronha, "Analytical solution of the nonlinear relativistic Boltzmann equation in the early universe and the thermalization of expanding systems", to appear.

Speaker: Jorge Noronha (University of Sao Paulo)

poster_boltzmann.pdf

4:30 PM Anisotropic flow fluctuations in heavy ion collisions at the LHC energy with HYDJET++ model

The LHC data on elliptic and triangular flow fluctuations from PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analysed and interpreted within the HYDJET++ model. The final state in HYDJET++ represents the superposition of two independent components: the soft state (parametrization of relativistic hydrodynamics with preset freeze-out conditions) and hard state (multi-paron fragmentation taking into account medium-induced partonic energy loss and nuclear shadowing effect). The simple modification of the model via introducing the distribution over spatial anisotropy parameters allows us to reprоduce the basic features of anisotropic flow pattern at the LHC including event-by-event flow fluctuations.

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

Petrushanko_QM15.pdf

4:30 PM Anisotropic hydrodynamics for a mixture of quark and gluon fluids

Relativistic hydrodynamics has been a fundamental tool to understand the evolution of matter in heavy-ion experiments at RICH and LHC. Despite the success of second order viscous hydrodynamics in reproducing collective behavior and particle spectra, there are still theoretical shortcomings that may question the validity of the approach in heavy-ion experiments conditions. Large gradients and fast longitudinal expansion produce very large pressure corrections, in contrast to the founding hypothesis of small deviation from local equilibrium and the perturbative treatment viscous corrections. One way to address this problem is anisotropic hydrodynamics. Most of the theoretical investigations about hydrodynamics started from a kinetic underlying substrate of a single species of particles. Unfortunately the striking agreement of anisotropic hydrodynamics with the exact solution of the Boltzmann equation was not preserved in the case of a mixtures of quarks and gluons. We recently extended the anisotropic hydrodynamics prescription for massless particles in 1+1-dimensions to the case of mixtures of fluids, largely improving the agreement with the exact solutions compared to previous works [1-3]. We allow quarks and gluons to have different momentum scales during the evolution and a non vanishing baryon chemical potential. We take the dynamical equations from the zeroth, the first and the second moment of the Boltzmann equation [4]. We performed a test of the new formulation, comparing the results of anisotropic hydorodynamics with the exact solution of the Boltzmann equation for a mixture of fluid in the Bjorken flow limit, finding a very good agreement [5]. [1] W.Florkowski, R.Maj, R.Ryblewski, M.Strickland, Phys.Rev.C87 (2013) 3, 034914. [2] W.Florkowski, R.Maj, Acta Phys.Polon.B44 (2013) 10, 2003-2017.[3] W.Florkowski, O.Madetko, Acta Phys.Polon.B45 (2014) 1103. [4] L.Tinti, W.Florkowski, Phys.Rev.C89 (2014) 3, 034907. [5] W.Florkowski, E.Maksymiuk, in progress

Speaker: Ewa Maksymiuk (Jan Kochanowski University)

Poster_QM2015_EM.pdf

4:30 PM Are charmed mesons thermalized in heavy ion collisions at RHIC and LHC?

Studying the charmed hadron production is a particularly useful tool to probe properties of hot and dense matter created in ultrarelativistic heavy ion collisions. It allows one also to extract the information about mechanisms of in-medium heavy quark thermalization. In this talk, the phenomenological analysis of various characteristics of charmed hadrons (J/Psi and D mesons) in heavy ion collisions at RHIC and LHC has been done in the frameworks of two-component HYDJET++ model. Among other heavy ion event generators, HYDJET++ focuses on the detailed simulation of jet quenching effect taking into account medium-induced radiative and collisional partonic energy loss (hard "non-thermal" component), and also reproducing the main features of nuclear collective dynamics by the parametrization of relativistic hydrodynamics with preset freeze-out conditions (soft "thermal" component). The charmed meson production pattern in heavy ion collisions at RHIC and LHC is reproduced by HYDJET++ simulations. The possibility of thermalization of J/Psi and D mesons at RHIC and LHC energies is discussed.

Speaker: Igor Lokhtin (Skobeltsin Institute of Nuclear Physics, Lomonosov Moscow State University (RUSSIA))

hydjet-charm_qm15.pdf

4:30 PM ATLAS measurement of the pseudorapidity multiplicity correlation in Pb+Pb collisions

ATLAS measurements of the longitudinal multiplicity correlation are presented. These correlations are sensitive to the early time dynamics, one of the most poorly constrained stages in the evolution. These measurements suggest sources of fluctuation that seem to be directly related to the forward-backward asymmetry in the initial geometry, and they are important for understanding the correlation of event activities between disconnected rapidity ranges.

Speaker: Mingliang Zhou (State University of New York (US))

QM15_poster_ver1_Mingliang.pdf

4:30 PM Azimuthal anisotropies of reconstructed jets in Pb + Pb collisions at √ sNN = 2.76 TeV in a multiphase transport model

Azimuthal anisotropies of reconstructed jets [$v_{jet}^{n} (n = 2,3)$] have been investigated in Pb + Pb collisions at the center of mass energy $√s_{NN} = 2.76 TeV$ within a framework of a multiphase transport (AMPT) model. The $v_{jet}^{2}$ is in good agreement with the recent ATLAS data. However, the $v_{jet}^{3}$ shows a smaller magnitude than $v_{jet}^{2}$ , and approaches zero at a larger transverse momentum. It is attributed to the path-length dependence in which the jet energy loss fraction depends on the azimuthal angles with respect to different orders of event planes. The ratio $v_{jet}^{n}$ /$ε_{n}$ increases from peripheral to noncentral collisions, and $v_{jet}^{n}$ increases with the initial spatial asymmetry ($ε_n$) for a given centrality bin. These behaviors indicate that the $v_{jet}^{n}$ is produced by the strong interactions between jet and the partonic medium with different initial geometry shapes. Therefore, azimuthal anisotropies of reconstructed jet are proposed as a good probe to study the initial spatial fluctuations, which are expected to provide constraints on the path-length dependence of jet quenching models.

Speaker: Maowu Nie (Shanghai Institute of Applied Physics (SINAP))

niemaowu_233.pdf

4:30 PM B meason analysis with CMS

Hadrons with heavy quarks are promising probes to investigate the detailed properties of hot and dense medium generated by heavy-ion collisions at collider energies. Since heavy quarks are sensitive to the transport properties of the medium, the energy-loss pattern of them is expected to be quite different from that of light quarks in a strongly-interacting matter. On the other hand, in order to elicit the actual effects caused by the hot and dense medium, it is necessary to understand the cold nuclear matter effect in pA collisions. For example, the pPb data is expected to provide a baseline for the study of the b-quark energy loss in medium produced by PbPb collisions. Therefore, the CMS Collaboration at the Large Hadron Collider (LHC) has analyzed the production cross sections of $B^{+}$, $B^{0}$, $B^{0}_{s}$ mesons in pPb collisions as a function of rapidity and the transverse momentum at the nucleon-nucleon center-of-mass energy of 5.02 TeV . In addition, the nuclear modification factors of the B mesons have been constructed using the theoretical pp reference spectra estimated by the perturbative Quantum ChromoDynamics (pQCD) model.

Speaker: Kisoo Lee (Korea University (KR))

QM2015_KisooLee_v4.pdf

4:30 PM Baryon number cumulant ratios at finite density in the strong-coupling lattice QCD

Cumulants of conserved charges contain information of fluctuations across the phase boundary, then can be the signal of criticality of the QCD phase transition. The net-proton number cumulant ratios observed at RHIC show non-monotonic behavior as a function of the incident energy. In order to confirm the conjecture that the non-monotonic behavior could suggest the existence of the QCD critical point [1], we need calculation of cumulant ratios hopefully in lattice QCD at finite density. We have recently calculated the cumulant ratios of net baryon numbers at finite density in the chiral limit in the strong-coupling lattice QCD [2]. Fluctuation effects beyond the mean field treatments are included in the auxiliary field Monte-Carlo method [3]. We find that $\kappa\sigma^2$ show oscillatory behavior; one negative valley around the phase boundary is sandwiched by two positive peaks as a function of $T$. With increasing lattice size, the negative $\kappa\sigma^2$ region is narrowed while the amplitude grows. This behavior may be in agreement with the potential surface argument [1] and the scaling function analysis [4]. In the presentation, we will briefly introduce the strong-coupling lattice QCD, and show results of higher-order cumulant ratios around the phase boundary. We may also discuss recent developments including $1/g^2$ effects in the strong-coupling expansion. [1] M. A. Stephanov, Phys. Rev. Lett. 107 (2011), 052301. [2] T. Ichihara, K. Morita, A. Ohnishi, to be submitted. [3] T. Ichihara, A. Ohnishi, and T. Z. Nakano, PTEP 2014 (2014), 123D02. [4] B. Friman, F. Karsch, K. Redlich, and V. Skokov, Eur. Phys. J. C71 (2011), 1694.

Speaker: Akira Ohnishi (Kyoto University)

QM2015-AO.pdf

4:30 PM Baryon Number Fluctuations and Quark Correlations in the CGC Framework

We calculate the two particle correlation function for the net baryon number fluctuations using the saturation/Color Glass Condensate (CGC) framework in proton-nucleus and heavy-light ion collisions. We show that the main contribution to the net baryon number fluctuations at mid-rapidity comes from $q\bar{q}$ pair production in the transverse plane. There are three intrinsic length scales associated with this process: the transverse size of the baryon fluctuation $r_\perp$, the inverse of the saturation scale $Q_s^{-1}$ and the inverse of the mass $M^{-1}_{q(\bar{q})}$ for heavy massive quarks. We identify two regimes determined by the dominant scale $R_{max}= \text{max} (Q_s^{-1},M^{-1})$ and discuss in detail the properties of each regime as one varies the transverse scale of the baryon fluctuation $r_\perp$. In proton-nucleus collisions the net baryon correlation function is suppressed when $r_\perp > R_{max}$, while for heavy-light ion collisions this correlation extends up to the typical transverse size of the nucleus. These baryon number fluctuations generate non-trivial correlations which may propagate into the subsequent hydrodynamical evolution of the expanding fireball.

Speaker: Douglas Wertepny (The Ohio State University)

4:30 PM Baryon number fluctuations around an expanding Bjorken background

Baryon number density perturbations could provide a possibility to access baryon number susceptibilities and the heat conductivity of a quark gluon plasma. We use a background-fluctuation splitting and a Bessel-Fourier decomposition for the fluctuating part of the fluid dynamical fields with respect to the azimuthal angle, the radius in the transverse plane and rapidity. We examine how the time evolution of linear perturbations depends on the equation of state as well as on shear viscosity, bulk viscosity and heat conductivity for modes with different azimuthal, radial and rapidity wave numbers. Finally we discuss how this information is accessible to experiments in terms of the transverse and rapidity dependence of the net baryon number correlation function (baryon minus anti-baryon) in high energy nuclear collisions.

Speaker: Dr Mauricio Martinez Guerrero (The Ohio State University)

4:30 PM Beam energy dependence of d and dbar productions in Au+Au collisions at RHIC

The production of light nuclei with small binding energy such as deuterons, can be used to study the freeze-out properties and local baryon density in high-energy nuclear collisions. The azimuthal anisotropic results of protons and deuterons have shown that the coalescence is the dominant process for the light nuclei production at later stage of the evolution. In this talk we present a systematic study of colliding energy, centrality, and transverse momentum dependence of mid-rapidity deuteron and anti-deuteron production, measured by the STAR experiment, from Au+Au collisions at RHIC at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV. Deuterons, protons and their anti-particles are identified using the time projection chamber (TPC) and time-of-flight detector (TOF). Proton and anti-proton yields are corrected from Lambda and anti-Lambda decays, respectively. The $B_2$ parameters, defined as ($N(d)/N^2(p)$), which measure the phase space density for nucleons show a difference between $B_2(d)$ and $B_2(\bar{d})$ and the difference becomes stronger at lower collision energy or higher baryon density region. These observations may imply that baryon and anti-baryon freeze-out at different densities. These new results will be discussed in light of data collected from AGS to LHC energies. In addition, the results will also be compared with transport model calculations.

Speaker: Dr Ning Yu (Central China Normal University CCNU)

QM15poster_ningyu.pdf

4:30 PM Beam energy dependence of Specific Heat in Ultra-relativistic Heavy-Ion Collisions

Experiments at RHIC and LHC are on the quest to unearth the nature of the QCD phase transition and to get a glimpse of how matter behaves at such extreme conditions. Phase transitions are governed by a set of thermodynamic parameters, like, temperature ($T$), pressure, entropy, and energy density ($E$), and can be further characterized by their response functions, like, specific heat, compressibility, and susceptibility. In thermodynamics, the heat capacity ($C$) is defined in terms of the ratio of the event-by-event fluctuations of the energy of a part of a finite system in thermal equilibrium to the energy ${(\Delta E^2)} = {T^2}C(T)$. This can be applied for a locally thermalized system produced during the evolution of heavy-ion collisions. But for a system at freeze-out, specific heat can expressed in terms of the event-by-event fluctuations in temperature of the system where volume is fixed: $ \frac{1}{C} = \frac{(\langle T^2 \rangle - \langle T \rangle ^2 )}{\langle T \rangle ^2}$. We define the specific heat as the heat capacity per pion multiplicity within the experimentally available phase space in rapidity and azimuth. For a system in equilibrium, the mean values of temperature and energy density are related by an equation of state. However, the fluctuations in energy and temperature have quite different behavior. Energy being an extensive quantity, its fluctuations have a component arising from the volume fluctuations, and not directly suited for obtaining the heat capacity. Here, we obtain the specific heat for heavy-ion collisions at SPS, RHIC beam energy scan energies and for LHC energy. Experimental results from NA49, STAR, PHENIX, PHOBOS and ALICE are combined to obtain the specific heat as a function of beam energy. The results are compared to results from AMPT event generator, HRG model and lattice calculations. We also present local hot spot search at LHC energy for better understanding the collision dynamics.

Speaker: Tapan Nayak (Department of Atomic Energy (IN))

QM2.pdf

4:30 PM Beyond the thermal model

The statistical hadronization (or thermal) model was initially developed by Hagedorn for hadron collisions above 10 GeV/c primary laboratory momentum [1]. In relativistic heavy-ion physics, many authors have developed it further and compared to a large amount of data in particular for hadron production rates, e.g. [2,3,4], where it yields excellent results. To decide whether the system is indeed in thermal equilibrium, the distribution functions rather than production yields are decisive: In the transverse momentum distributions of produced particles, deviations from thermal behaviour plus collective expansion occur beyond about 8 GeV/c. Not only the rapidity distributions of net baryons, but also the pseudorapidity distributions of produced mesons deviate from pure thermal behaviour: the thermal model does not generate a plateau in dN/dy, or a dip in dN/deta. Such non-equilibrium effects can to a certain extent be accounted for in a relativistic diffusion model [5,6] with three sources - two fragmentation sources, and a mid-rapidity source arising from gluon-gluon collisions - that merges with the thermal model only for time to infinity. Given the short interaction times of AuAu at RHIC or PbPb at LHC, the fragmentation sources still contribute substantially, providing good results when compared [6,7] to data from PHOBOS and ALICE, and also for asymmetric systems such as dAu at RHIC and pPb at LHC. [1] R. Hagedorn, Nuovo Cim. Suppl. 3, 147 (1965) [2] P. Braun-Munzinger, J. Stachel, J. Wessels, N. Xu, Phys. Lett. B 344, 43 (1995) [3] A. Andronic, P. Braun-Munzinger, J. Stachel, Nucl. Phys. A 772, 167 (2006) [4] J. Manninen, F. Becattini, Phys. Rev. C 78, 054901 (2008) [5] G. Wolschin, Eur. Phys. J. A 5, 85 (1999) [6] G. Wolschin, M. Biyajima, T. Mizoguchi, N. Suzuki, Phys. Lett. B. 633, 38 (2006); Ann. Physik 15, 369 (2006) [7] G. Wolschin, J. Phys. G 40, 45104 (2013); Phys. Rev. C 91, 014905 (2015)

Speaker: Georg Wolschin (Heidelberg University)

QM2015_posterx.pdf

4:30 PM Bottom cross-section measurement in $p$+$p$ collisions using dielectrons at $\sqrt{s}=200$ GeV measured by the PHENIX Experiment at RHIC

The dielectron mass spectrum is a unique probe to directly access the different stages of a heavy-ion collision. The intermediate ($1< m_{e^+e^-}<3$ GeV/$c^2$) and high ($4<m_{e^+e^-}<8$ GeV/$c^2$) mass regions are dominated by semi-leptonic decays of open charm and beauty respectively, and so provide information about the heavy flavor dynamics. We will present the current status on the bottom cross-section extracted in $p$+$p$ collisions. The method utilizes the double differential fit done in $m_{{e^+}e^{-}}$ and $p_T$ space, which provides sensitivity to the regions where either charm or bottom dominates. A comparison to the $p_T$ spectrum and cross-section extracted from the $d$+$Au$ dielectron mass spectrum using the same technique will be presented.

Speaker: Deepali Sharma (Stony Brook University)

poster_qm12.pdf

4:30 PM Bottomonia suppression in 2.76 TeV Pb-Pb collisions

We compute the QGP suppression of $\Upsilon(1s)$, $\Upsilon(2s)$, and $\Upsilon(3s)$, $\chi_{b1}$ and $\chi_{b2}$ states in $\sqrt{s_{NN}}=2.76$ TeV Pb-Pb collisions. Using the suppression of each of these states, we estimate the inclusive $R_{AA}$ for the $\Upsilon(1s)$ and $\Upsilon(2s)$ states as a function of $N_{\rm part}$, $y$, and $p_T$ including the effect of excited state feed down. We find that our model provides a reasonable description of recently obtained CMS results for the $N_{\rm part}$-, $y$-, and $p_T$-dependence of $R_{AA}$ for both the $\Upsilon(1s)$ and $\Upsilon(2s)$. Comparing to our previous results, we find a flatter rapidity dependence, thereby reducing some of the tension between our model and ALICE forward-rapidity results for $\Upsilon(1s)$ suppression.

Speaker: Michael Strickland (Kent State University)

bottomonia.pdf

4:30 PM Bottomonium production in coupled Langevin and transport approach

In heavy ion collisions, quarkonium is produced in a rapidly thermalized deconfined medium. Quarkonium production can be understood in terms of Langevin dynamics of heavy quarks interacting through medium modified potential [1]. This framework was used sucessfully to understand charmonium production at RHIC [1,2] including recombinant production [2] when realistic values of the heavy quark diffusion constant are used together with a lattice QCD inspired potential. It also explains the J/psi production at LHC including its centrality independence [3]. We extend this framework to upsilon production by including the thermal dissociation of formed bottomonia. This is done with a transport (local rate) equation followed by Langevin dynamics of the correlated $Q\bar{Q}$ states. The bulk evolution of the medium is treated using MUSIC, a 3+1-dimensional hydrodynamical simulator of heavy ion collisions, while we make use of the latest lattice results on the $Q\bar{Q}$ potential. We make prediction for the bottomonium production at full LHC energy. [1] C. Young and E. Shuryak, Phys.Rev. C79 (2009) 034907 [2] C. Young and E. Shuryak, Phys.Rev. C81 (2010) 034905 [3] C. Young et al, Phys.Rev. C86 (2012) 034905

Speaker: Clint Young (M)

4:30 PM Breaking the degeneracy of hard+soft modelling

Current freedom to adjust competing effects of the jet-medium coupling, the jet-path length, eccentricities, and fluctuations make it difficult to deceide between pQCD tomographic or AdS holographic paradigms. We test jet tomographic and holographic models in a broad range of state-of-the-art event-by-event fluctuating bulk sQGP background evolutions and compare predictions of leading-hadron fragment and reconstructed jet-nuclear modifications factors as well as high-pT azimuthal harmonics. New measures of other jet correlation observables will be suggested to help break the current degeneracy of hard+soft modelling.

Speaker: Barbara Betz (Frankfurt University)

Betz_PosterQM2015.pdf

4:30 PM Broad eta Range Survey of 1/N dNch/deta at the LHC

We present the charged particle pseudo-rapidity density in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV with an extended centrality dependence, and in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV over a broader pseudo-rapidity range. In the forward regions where the signal is dominated by secondary particles produced in surrounding material, we use a data-driven correction to extract the charged primary particle density. We compare our results to predictions of various models, and show that none of these models capture all of the aspects of the full distribution. This talk extends the previous results reported by ALICE into more peripheral collisions and with higher granularity for Pb-Pb and broader range in pseudo-rapidity for both p-Pb and Pb-Pb.

Speaker: Christian Holm Christensen (University of Copenhagen (DK))

poster.pdf

4:30 PM Calculation of high-order cumulant with canonical ensemble method in lattice QCD

Confinement/deconfinement phase transition is one of the most interesting subject in finite density QCD. For example, high-order cumulant of net quark number that has been observed in experiments shows a specific behavior around the phase transition line. However, sign problem caused by complex action makes it difficult to numerical calculation of it. In this study we realize the calculation of high-order cumulant with a combination of "canonical ensemble method" and hopping parameter expansion in heavy quark region. Also, we study a finite density phase transition from the specific behavior of high-order cumulants and its volume dependence.

Speaker: Asobu Suzuki (University of Tsukuba)

poster.pdf

4:30 PM Calculation of k*/k+ ratio assuming the partial chemical equilibration

Production of K* in the relativistic heavy-ion collisions at LHC draws strong interest since the ratio involving K* mesons such as K*/pi or K*/K+ doesn’t fit to the statistical model calculations while most of other ratios fit nicely. The reason is possibly that the K* doesn’t chemically freeze-out at the same temperature $T_{ch}$ as other particles do. Rather K* maintains partial chemical equilibrium through the process $K* \rightarrow K+ + \pi$ until the thermal freeze-out temperature, $T_{th}$. In this presentation, after fitting the momentum spectra of measured hadrons and ratios involving them measured by the ALICE collaborations with a blast-wave model which assumes the chemical freeze-out at higher $T_{ch}$ and the thermal freeze-out at lower $T_{th}$, the ratio $K*/\pi$ is calculated from the parameters thus obtained assuming the partial chemical equilibration of K*, K and $pi$ until $T_{th}$, and the result is compared with the data.

Speaker: Kang Seog Lee (Chonnam National University)

qm2015-kslee.pdf

4:30 PM Centrality dependence of photon anisotropic flow at RHIC

We calculate elliptic and triangular flow of thermal photons for different collision centralities at RHIC using event–by-event hydrodynamic model with fluctuating initial conditions. Photon $v_3$ as a function of $p_T$ calculated with respect to the participant plane angle is found to be comparable to the elliptic flow parameter $v_2(p_T)$ for 0—20% centrality bin at RHIC. However, $v_2(p_T)$ rises much faster than $v_3(p_T)$ towards peripheral collisions and $v_3(p_T)$ is found to be largest for 20—40% centrality bin. We study the event-by-event distributions of $v_2$ and $v_3$ and their corresponding initial state anisotropies to understand the correlation between them. A significant linear correlation between $v_2$ and $\epsilon_2$ is observed at different $p_T$ values, however we do not see any correlation between photon $v_3$ and the initial triangularity $\epsilon_3$. This is unlike the case of hadrons where a clear mapping between hadronic $v_3$ and $\epsilon_3$ has been observed. We conclude that indirect effects of initial state fluctuations, such as buildup of large transverse flow velocity contribute significantly to the observed $v_3$ results beyond leading to an overall triangular geometry.

Speaker: Rupa Chatterjee

4:30 PM Characterization of the initial state and QGP medium from a combined Bayesian analysis of RHIC and LHC data

A primary goal of heavy-ion physics is the measurement of the fundamental properties of the quark-gluon plasma (QGP), notably its transport coefficients, such as the specific shear viscosity $\eta/s$. Since these properties are not directly measurable, one relies on a comparison of the data to computational models of the time-evolution of the collision to connect measured observables to the properties of the transient QGP state. The computational model parameters are tuned such that simulated observables optimally match experimental data. We employ a Bayesian model-to-data comparison method for extracting QGP properties [1303.5769, 1502.00339]. First, we choose a set of salient model parameters -- including physical properties such as $\eta/s$ -- then evaluate a modern event-by-event heavy-ion collision model at a small set of points in the multidimensional parameter space, varying all parameters simultaneously. We use a Gaussian process emulator to non-parametrically interpolate the parameter space, providing fast predictions at any point in parameter space with quantitative uncertainty. Finally, we systematically explore the parameter space with Markov chain Monte Carlo (MCMC) to obtain rigorous constraints on all parameters simultaneously, including all correlations. In this work, we apply the Bayesian methodology to the new TRENTO initial condition model [1412.4708] and standard MC-Glauber initial conditions, coupled to event-by-event viscous 2+1D hydrodynamics and UrQMD [1409.8164]. We calibrate several initial condition and medium parameters to experimentally observed particle yields, spectra, and flows from RHIC and the LHC. This systematic model-to-data comparison yields rigorous constraints on the nature of the initial state and on fundamental QGP medium properties. The method is general and easily extensible to future studies.

Speaker: Jonah Bernhard (Duke University)

poster.pdf

4:30 PM Characterizing flow fluctuations with moments

We present a complete set of multiparticle correlation observables for ultrarelativistic heavy-ion collisions. These include moments of the distribution of the anisotropic flow in a single harmonic, and also mixed moments, which contain the information on correlations between event planes of different harmonics. We explain how all these moments can be measured using just two symmetric subevents separated by a rapidity gap. This procedure is less demanding in terms of detector acceptance than the one based on several rapidity windows separated pairwise by gaps. These moments present a multi-pronged probe of the physics of flow fluctuations. For instance, they allow to test the hypothesis that event-plane correlations are generated by non-linear hydrodynamic response. They can be measured easily at LHC and even with detectors having smaller acceptance, and can be directly compared with theoretical calculations. We illustrate the method with simulations of events in A MultiPhase Transport (AMPT) model [1]. It is important to test if experimental data at LHC confirm these predictions. [1] R.S. Bhalerao, J.-Y. Ollitrault, S. Pal, Phys. Lett. B 742 (2015) 94

Speaker: Rajeev Bhalerao (TIFR)

poster_140.pdf

4:30 PM Characterizing the away-side jet, devoid of flow background, via two-particle and three-particle correlations in Au+Au collisions at $\sqrt{s_{NN}}$ = 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 themselves. We select events with a large recoil momentum ($P_x$) within a pseudorapidity ($\eta$) window of $0.5<\eta<1$ ($-1<\eta<-0.5$) 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 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 themselves. 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 & Purdue University)

QM15poster_Kun_v3.pdf

4:30 PM Charge Asymmetry Correlations to Search for the Chiral Magnetic Effect from Beam Energy Scan by STAR

STAR has reported the measurement of charge asymmetry correlations with respect to the event plane in search for the Chiral Magnetic Effect [1]. The charge separation parameter $\Delta$ after model-independent subtraction of elliptic flow ($v_2$) background, was measured to be 1.3$\pm$1.4(stat.)$_{-1.0}^{+4.0}$ (syst.)$\times10^{-5}$ for $20-40\%$ Au+Au collisions at 200GeV, consistent with zero.In this talk we report results obtained with higher statistics data. A statistically significant finite signal is observed. The improved statistical precision allows systematic studies of the charge separation and investigation of possible further physics background. It is found that the charge separation parameter $\Delta$ increases with decreasing centrality, but shows a weak beam-energy dependence. We also report the application of a multi-particle correlation method [2] for the measurement of charge separation with model-independent background subtraction by the mixed-event technique. By comparing correlation functions along and perpendicular to the event plane, potential upper limits are set on the charge separation parameter in the high statistics 200 GeV Au+Au data. These results will be discussed in terms of the possible Chiral Magnetic Effect and/or physics background. [1] L. Adamczyk et al. (STAR Collaboration) Phys. Rev. C **89**, 044908 (2014). [2] N. N. Ajitanand, R. A. Lacey, A. Taranenko, and J. M.Alexander, Phys. Rev. C **83**, 011901(R) (2011).

Speaker: Biao Tu (Central China Normal University)

QM15poster_tubiao.pdf

4:30 PM Charged hadron production and two-particle correlations in $^3$He+Au collisions at ${\sqrt{s_{NN}}}$ = 200 GeV measured with PHENIX detector

The high p$_T$ hadron suppression caused by the energy loss of partons traversing the hot and dense matter is found to be one of the evidences of Quark-Gluon-Plasma (QGP) formation in high-energy heavy-ion collisions. Measurements in p+A and d+A collision systems have been considered as a control-experiment to study cold nuclear matter effects without QGP formation. However, recent measurements of hydrodynamic flow behavior and long-range angular correlations in p+A, d+A, and high multiplicity p+p collisions have indicated that small but high-density systems could be produced in such collisions, although the minimum bias R$_{AA}$ is about unity. $^3$He+Au collisions have been delivered at RHIC in 2014 in order to perform a systematic study of small systems from p+p and d+Au to $^3$He+Au having different spacial anisotropy of initial states. In this poster presentation, we report the current status of charged hadron production and two-particle correlation measurements in $^3$He+Au collisions at ${\sqrt{s_{NN}}}$ = 200 GeV. Obtained results are compared between different collision systems.

Speaker: Sakiko Kudo (University of Tsukuba (JP))

4:30 PM Charged kaon- and $\phi$-reconstruction in Au+Au-collisions at 1.23 AGeV

In Au+Au-collisions at 1.23 AGeV incident energy, strangeness is produced below the free nucleon-nucleon threshold. In baryon dominated matter K$^+$ and K$^-$ mesons exhibit different properties, since only K$^-$ can be resonantly absorbed by nucleons. Although strangeness exchange reactions have been proposed to be the dominant channel for K$^-$ production in this energy regime, the production yield could also be explained in Ar+KCl-reactions at 1.76 AGeV based on a statistical hadronization model fit to the measured particle yields. To guarantee strangeness conservation, strangeness is calculated canonically within R$_c$ in these models, and therefore the ratio of $\phi$/K$^-$ is predicted to rise with decreasing beam energies and as a consequence the feed-down of $\phi$-mesons to kaons becomes important. In total 7.3 Billion 40% most central Au(1.23 GeV per nucleon)+Au collisions have been analyzed for this investigation. The data has been recorded with HADES and a substantially improved reconstruction method has been employed to reconstruct the hadrons with high purity in a wide phase space region. In this contribution, we present results on charged kaons and $\phi$-mesons. Supported by BMBF (05P12RFGHJ), HIC for FAIR, HGS-HIRe, H-QM and GSI.

Speaker: Ms Heidi Schuldes (Goethe-University Frankfurt)

poster_qm15_schuldes.pdf

4:30 PM Charged ρ meson in a magnetic field at finite temperature and chemical potential

The charged vector $\rho$ mesons in the presence of external magnetic fields at finite temperature $T$ and chemical potential $\mu$ have been investigated in the framework of the Nambu--Jona-Lasinio model. We compute the masses of charged $\rho$ mesons numerically as a function of the magnetic field for different values of $T$ and $\mu$. The self-energy of the $\rho$ meson contains the quark-loop contribution, i.e. the leading order contribution in $1/N_c$ expansion. It is found that the charged $\rho$ meson mass decreases as the magnetic field increases and drops to zero at a critical magnetic field $eB_c$. The charged vector meson condensation, i.e. the electromagnetic superconductor can be induced above the critical magnetic field. We find that at zero density, in the temperature range $200-500~ {\rm MeV}$, the critical magnetic field for charged $\rho$ condensation is in the range of $0.2-0.6~ {\rm GeV}^2$, which indicates that high temperature superconductor could be created at LHC.

Speaker: Ms Hao Liu (IHEP)

QM2015 海报.pdf

4:30 PM Charm and bottom nuclear modification in Cu+Au collisions at $\sqrt{s_{NN}}=200 GeV

Forward and backward rapidity measurements in heavy ion asymmetric collisions offer the opportunity to study the nuclear modification of particle yields versus path length, time inside the medium, particle densities and different mixtures of cold nuclear matter and quark-gluon plasma effects in the same collision. The PHENIX Experiment collected data from a large sample of Cu+Au collisions at $\sqrt{s_{NN}}$=200 GeV and, for the first time, with forward vertex detectors (FVTX) which enabled the study of displaced vertex muon decays from heavy flavor at backward and forward rapidities. Charm and bottom yields can be separated in inclusive single muon yields and bottom yield can also be obtained from J/$\psi$ vertex displacements. The status of this analysis will be presented.

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

4:30 PM Charm decay leptons in pA collisions within the CGC framework

We compute electron and muon productions from the charm semileptonic decays in proton-lead collisions at the LHC within the Color Glass Condensate framework. At the LHC energies, open heavy flavor and quarkonium productions are expected to have an access to the small-$x$ region of hadronic wavefunctions, where the nonlinear character of the dense gluon system becomes manifest. Leptonic channels of heavy flavor decays are important observables, but the information on the small-$x$ gluons are relatively indirect there. In this presentation, we will show electron and muon spectra of heavy-flavor decays at low-$P_\perp$ and their two-particle correlations. We will discuss in which kinematical region the saturation effects are well reflected in the lepton distributions.

Speaker: Hirotsugu Fujii (University of Tokyo)

QM.pdf

4:30 PM Charmonium suppression in QGP at LHC energy using temperature dependent formation time

The charmonium wavefunction is expected to expand with the temperature of the quark-gluon plasma (QGP) formed in the heavy-ion collision experiments. We model the effect of this expansion on the formation time of the charmonium bound states and eventually, the effect of this temperature dependent formation time on the $J/\psi$ suppression in the QGP medium. The effect of charm quark and anti-charm quark via recombination to form secondary charmonium states is also incorporated in the present work. A set of coupled rate equations is established which incorporates color screening, gluonic dissociation, collisional damping and recombination of uncorrelated $c$ and $\bar{c}$ pair in the QGP medium. The effect of light quarks is also evaluated. Shadowing as a cold nuclear matter (CNM) effect is also incorporated in the current work. The final $J/\psi$ suppression, thus determined as a function of centrality, is compared with the ALICE (low $p_T$) experimental data at both, mid rapidity and forward rapidity and CMS (high $p_T$) experimental data at mid rapidity obtained from the Large Hadron Collider (LHC) at center-of-mass energy, $\sqrt{s_{NN}} = 2.76$ TeV. We find that our predicted result on suppression depicts reasonably good agreement with the data. We also find that contribution of color screening in determining the total suppression of $J/\psi$ in QGP medium becomes insignificant due to employing temperature dependent formation time.

Speaker: Dr Madhukar Mishra (Birla Institute of Technology and Science Pilani, Pilani Campus)

QM2015_ID579.pdf

4:30 PM Chemical potential dependence of the critical quark mass with Many flavor approach

We discuss the QCD critical point at finite density through the study of many-flavor QCD, in which two light flavors and Nf massive flavors exist. Performing simulations of QCD with 2 flavors of improved Wilson fermions, we calculate probability distribution functions in many-flavor QCD at finite temperature and density, where the reweighting technique is used to add the dynamical effect of massive flavors and the chemical potential. From the shape of the distribution functions, we determine the critical surface separating the first order transition and crossover regions in the space spanned by the light and massive quark masses and the chemical potentials. It is found that the critical massive quark mass becomes larger as the chemical potential increa