Hot Quarks 2014

21 Sept 2014, 20:00 → 27 Sept 2014, 20:35 Europe/Madrid

^6th Workshop for young scientists on the physics of ultrarelativistic nucleus-nucleus collisions

Monday 22 September

Session 1: p+A correlations and initial state

session 1

Convener: Boris Hippolyte (Institut Pluridisciplinaire Hubert Curien (FR))

1 Quick introduction

Speaker: Boris Hippolyte (Institut Pluridisciplinaire Hubert Curien (FR))

2 Experimental overview of p(d)+A physics

Speaker: Roberto Preghenella (CERN)

Slides Roberto_Preghenella.pdf

3 Soft probes of p+Pb and Pb+Pb collisions in the ATLAS experiment at the LHC

Physics studies of p+Pb and Pb+Pb collisions in the ATLAS experiment at the LHC at low transverse momenta include the charged particle multiplicities, their scaling with the number of participating nucleons as well as pT-spectra and their modification with respect to the spectra of proton-proton collisions. Recent ATLAS results on the total charged particle multiplicities and spectra in p+Pb and Pb+Pb will be reviewed. The collective phenomena arising from the azimuthal asymmetry in the initial shape of the interaction region and maintained by the subsequent system evolution and can be in detail studied by analyzing charged particle azimuthal distributions. The recent measurements of flow harmonics in p+Pb and Pb+Pb collisions will be presented. In particular, the presentation will focus on flow harmonics fluctuations and their relation to fluctuations in the initial state of Pb+Pb collisions.

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

Slides Sooraj_Krishnan_Radhakrishnan.pdf

4 Transverse momentum distributions of identified particles in p-Pb collisions at $\sqrt{s_{NN}} = 5.02\ TeV$ measured with ALICE

Transverse momentum distributions of identified particles have been measured in several multiplicity classes in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. This can improve the understanding of possible collective effects in high multiplicity events. Furthermore the production mechanism of deuterons can be studied, since p-Pb collisions bridge the charged multiplicity gap between pp and low multiplicity Pb-Pb collisions. Particles are reconstructed with the central barrel detectors over a wide transverse momentum range (0 GeV/$c$ up to 15 GeV/$c$), exploiting different identification techniques. Primary charged particles ($\pi\mathrm{^{\pm}, K^{\pm}, p, \bar{p}, d\ and\ \bar{d}}$) are identified by their specific energy loss ($\mathrm{d}E/\mathrm{d}x$) and time-of-flight. Weakly decaying particles ($\mathrm{K^{0}_{s}, \Lambda\ and\ \bar{\Lambda}}$) are identified by their characteristic decay topology. Particle-production yields, spectral shapes and particle ratios have been measured in several multiplicity classes. Comparisons with models and results obtained in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV at the LHC will be shown.

Speaker: Jonas Anielski (Westfaelische Wilhelms-Universitaet Muenster (DE))

Slides anielski_hotquarks14_final.pdf

09:55 Coffee break

5 $\Upsilon$ production in hadron collisions at forward rapidity with ALICE at the LHC

Ultrarelativistic heavy-ion collisions produce strongly interacting matter at high temperature and energy density. Under these extreme conditions a deconfined partonic state, called Quark-Gluon Plasma (QGP), is formed. The measurement of quarkonia (charmonia and bottomonia) in AA collisions is expected to provide essential information about the QGP properties. In pp collisions high precision data serve as crucial test for several competing models of quarkonium hadroproduction and provide the reference for the measurements in heavy-ion collisions, while pA collisions are useful to disentangle hot and cold nuclear matter effects. In the ALICE Muon Spectrometer, bottomonium production can be measured at forward rapidity ($2.5 < y < 4$) and down to $p_{\mathrm{T}} = 0$ via the dimuon decay channel. The latest results on $\Upsilon$ production in pp, Pb-Pb and p-Pb collisions are discussed and compared to various theoretical predictions.

Speaker: Massimiliano Marchisone (Universita e INFN (IT))

Slides Massimiliano_Marchisone.pdf

6 The Impact of e+A Collisions on Nuclear PDFs

From the most recent experimental data collected at CERN's Large Hadron Collider, it was realized that the outcome of high-energy proton-nucleus collisions is very sensitive to the fact that the nucleon positions in the nucleus fluctuate event by event. In order to be able to precisely extract from future measurements interesting properties of quantum chromodynamics in the strong field regime, we implement such fluctuations into theoretical predictions for electron-nucleus scattering and evaluate the impact that these predictions have on nuclear patron distribution functions.

Speaker: Manoel R. Moldes

Slides Manoel_Moldes.pdf

7 Measurement of W-boson production in p--Pb collisions at $\sqrt{\mathrm{s}_{\rm NN}}=5.02$ TeV with ALICE at the LHC

In hadronic collisions, W bosons are produced in initial hard scattering processes and they are not affected by the strong interaction. They have been suggested as standard candles for luminosity measurements and their measurement can improve the evaluation of detector performances. In nucleus-nucleus and proton-nucleus collisions, W bosons allow one to check the validity of binary collision scaling and to study the nuclear modification of parton distribution functions. The production of W bosons in p--Pb collisions at $\sqrt{\mathrm{s}_{\rm NN}}=5.02$ TeV is measured via the contribution of W decays to the inclusive $p_T$-differential muon yield reconstructed with the ALICE muon spectrometer at forward ($2.03<{y}^{\mu}_{\rm cms}<3.53$) and backward ($-4.46<{y}^{\mu}_{\rm cms}<-2.96$) rapidity. After a presentation of the motivation for the study of W bosons and a description of the ALICE muon spectrometer, the latest results on W-boson production at forward and backward rapidity in p--Pb collisions will be shown and discussed.

Speaker: Jianhui Zhu (Central China Normal University CCNU (CN))

Slides HotQuarks2014_Jianhui_v7.pdf

11:40 Discussion

Session 2: Initial state II

Convener: Javier L Albacete (Universidad de Granada)

8 W boson studies in pPb and PbPb collisions with CMS

The electroweak W bosons do not participate in the strong interaction, and thus constitute clean probes of the initial state of nuclear collisions. They provide a unique constraint on the nuclear parton distributions, in particular on the antiquarks from the sea. A first analysis of PbPb data has confirmed the medium-blind characteristic of the electroweak bosons. With the new pPb data, collected at the beginning of 2013, nuclear matter without the creation of a hot medium can hence be studied. Being 10 times more prevalent than Z bosons, the yield of W bosons recorded from pPb collisions allows precise comparisons to theoretical predictions. A yield of approximately 20,000 W is observed in pPb collisions in both the muon and electron channels. In this talk the CMS measurements of W bosons in PbPb at $\sqrt{s_{NN}}$ = 2.76 TeV and from the new pPb data at $\sqrt{s_{NN}}$ = 5.02 TeV are reported. The charge asymmetry, forward/backward asymmetry and fully corrected yields will be shown.

Speaker: Emilien Chapon (Ecole Polytechnique (FR))

Slides Emilien_Chapon.pdf

9 Modelling jet quenching with Quenching Weights

We present a phenomenological study of the single- and double-inclusive suppression data of high-pT particles in central Pb-Pb collisions at LHC. The analysis is based on quenching weights for medium-induced gluon radiation computed in the multiple soft scattering approximation and embedded in a hydrodynamic description of the bulk medium.

Speaker: Mrs Carlota Andrés (Universidade de Santiago de Compostela)

Paper hqproceedings.pdf

10 High pT probes of proton-lead collisions with the ATLAS detector

Measurements of high pT processes in ultrarelativistic proton-nucleus collisions are sensitive to changes in the partonic densities arising from the presence of the high-density nuclear environment. Additionally, such measurements serve as a benchmark of the so called "cold nuclear matter" effects, providing the context within which to understand the strong suppression of high pT processes observed in nucleus-nucleus collisions. Furthermore, measurements of the centrality dependence of jet production at forward (proton-going) rapidities may even shed light on the behavior of the proton wavefunction at large Bjorken-x. The latest ATLAS results for inclusive jets and charged particles in 28/nb of 5.02 TeV proton-lead collisions at the LHC are presented. The centrality in these collisions is characterized through the sum of the transverse energy in the lead-going forward calorimeter. The nuclear modification factors RpPb and RCP are presented for jets and charged particles as a function of transverse momentum, rapidity and centrality.

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

Slides dvp-HotQuarks14-9-22-14.pdf

18:00 Coffee Break

11 Study of Z boson production in pp, pPb and PbPb collisions in CMS

The Z boson is a new probe of ultra-relativistic heavy-ion collisions, which became accessible at the LHC energies. Unambiguously detected when decaying in the dilepton channel, it can help to constrain nuclear parton distribution functions, it can serve as a standard candle for initial state effects, and it represents an in-situ probe for binary scaling in the final state of the collisions. We will report on the Z boson measurements with the CMS detector, using pp and pPb data recorded in 2013, and PbPb data recorded in 2011. The transverse momentum and rapidity differential cross sections of Z bosons measured in both pp and PbPb collisions at 2.76 TeV, as well as in pPb collisions at 5.02 TeV will be presented. This provides access to the low Bjorken x region, which is lacking precision experimental measurements needed by nuclear PDF parametrizations. Nuclear modification factors as a function of transverse momentum, rapidity and centrality for PbPb collisions will be shown, together with forward-backward ratios for pPb collisions.

Speaker: Anna Zsigmond (Wigner RCP, Budapest (HU))

Slides HQ2014_AZsigmond_v2.pdf

12 The impact of the LHC nuclear program on nPDFs

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 the Hessian reweighting technique we give a quantitative estimate of the modification of nPDFs due to novel data, and also determine wether or not performing a new extraction of nPDFs is mandatory at this point. The thorough understanding of partonic behaviour in a nuclear medium shall be of great relevance for future electron-ion and proton-ion colliders.

Speaker: Dr Maria Zurita (Universidade de Santiago de Compostela)

Slides HotQuarks-Zurita.pdf

13 Quantized fermions in semi-classical Yang-Mills evolution

The “standard model” of relativistic heavy-ion collisions describes the early stage of an hadronic collission by the Color Glass Condensate. The studies of anisotropically expanding plasmas show that non-Abelian plasmas isotropize fast enough thanks to the Chromo-Weibel instability. Recent work involves the novel incorporation of quantized fermions in the semi-classical Yang-Mills evolution.

Speaker: maximilian attems (U)

19:25 More discussion

Tuesday 23 September

Session 3: Jets I

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

14 Experimental overview of Jets

Speaker: Dr Christof Roland (Massachusetts Inst. of Technology (US))

Slides HQ_CRoland_v1.pdf HQ_CRoland_v1.ppt

15 Study of the neutral mesons in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76~TeV in the ALICE experiment at LHC

$\pi^{0}$ and $\eta$ mesons are probes for studying, among other interesting phenomena, the energy loss of partons traversing the hot and dense medium, the Quark-Gluon Plasma, that is formed in heavy-ions collisions. In addition, the study of $\pi^{0}$ and $\eta$ mesons in Pb-Pb collisions is necessary for the direct-photon measurement since these mesons constitute its most important background. The ALICE experiment at the LHC measures neutral meson spectra in Pb-Pb collisions with several complementary methods. One of these is the Photon Conversion Method (PCM), based on the reconstruction of photon conversions by the ALICE Inner Tracking System (ITS) and the Time Projection Chamber (TPC). This method provides a measurement at low $p_{\mbox{T}}$, down to 0.4 GeV/$c$ for the $\pi^{0}$ and to 1 GeV/$c$ for the $\eta$, with a large significance. It uses $e^{+}e^{-}$ pairs from photon conversions in the detector material to obtain a clean photon sample. Neutral mesons are then reconstructed via the two gamma decay channel. The $\pi^{0}$ has been measured with 2010 data and the results obtained have been published recently. The $\eta$ was more challenging to measure with the 2010 data as the available statistics was not sufficient to have a significant measurement. On the other hand, the large statistics of the 2011 data allows a measurement of the differential invariant cross section of the $\eta$ meson as function of transverse momentum up to a $p_{\mbox{T}}$ of about 10 GeV/$c$ in different centrality classes. The $\pi^{0}$ measurement from data collected with the ALICE experiment during the 2010 Pb-Pb run and, if possible, the current status of the $\eta$ meson analysis from data collected during the 2011 Pb-Pb run will be presented.

Speaker: Lucia Leardini (Ruprecht-Karls-Universitaet Heidelberg (DE))

Slides HQ2014_LeardiniV2.pdf

16 Neutral pion production in $\sqrt{s_{NN}}$=200 GeV Cu+Au collisions at PHENIX

Cu+Au collisions at RHIC generate asymmetric initial geometries and densities in both azimuth and rapidity. High $p_T$ $\pi^0$s produced in $\sqrt{s_{NN}}$ = 200 GeV Cu+Au collisions provide new environments to study parton energy loss in the Quark Gluon Plasma. including very central events where the Cu nucleus is enveloped by the Au nucleus. By measuring $\pi^0$ yields in $\phi$ relative to the event plane, we can probe different core-corona regions in these very central events and study the path length dependence of energy loss in various lopsided initial geometries. PHENIX has observed the suppression of $\pi^0$s as a function of the azimuthal angle with respect to the event plane in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions and found it consistent with a larger that quadratic path length dependence suggesting a non-perturbative energy loss model applies. The unique collision geometries available in Cu+Au provide new settings to explore and possibly confirm this path length dependence. The status of the Cu+Au $\pi^0$ analysis will be presented.

Speaker: Dr Sarah Campbell (Iowa State University)

Slides HotQuarks_Campbell.pdf

17 Jet measurements in Heavy Ion collisions with CMS

One of the signatures of the strongly interacting medium produced in heavy ion collisions is the suppression of high-transverse momentum ($p_{\rm T}$) jets or so called ‘quenched jets’. In this talk, we present detailed measurements of nuclear modification factors and energy flow of quenched jets with the CMS detector. Those new results extend previous measurements to large angle with respect to the quenched jets and extend the transverse momentum range to lower $p_{\rm T}$. We use the high statistics pp, pPb and PbPb data taken in 2011-13 employing a new data-driven method to estimate the underlying event level from the forward calorimeter energy distribution, taking into account possible flow modulation. We will also look at the flavor dependence of energy loss of jets by looking at heavy flavor tagged b-jets in these systems.

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

Slides HQ_Sept2014_ResultsJetsHI_raghav_v6.pdf

10:05 Coffee break

18 Decoding the quark-gluon plasma with jet quenching observables

The modifications of jets created in heavy-ion collisions at LHC energies enables us to study microscopic features of the quark-gluon plasma. The inherent hierarchy of scales governing the jet evolution allows to distinguish a leading jet structure, which interacts coherently with the medium as a single color charge, from softer sub-structures, which will be sensitive to effects of color decoherence. We show that this picture is consistent with experimental data on reconstructed jets at the LHC. In particular, we demonstrate that effects due to color decoherence are manifest in the excess of soft particles measured in fragmentation functions in Pb-Pb compared to proton-proton collisions. Finally, we discuss the sensitivity of the different observables to the jet quenching parameter $\hat q$ of the plasma as well as to the finite mean-free-path of the medium.

Speaker: Dr Konrad Tywoniuk (Universitat de Barcelona)

Slides HQ2014_KT.pdf

19 Jet suppression in ultrarelativistic heavy ion collisions

D mesons are considered to be excellent probes of QCD matter created in ultra relativistic heavy ion collisions. Here we examine charm quark suppression in central Au+Au collisions at RHIC, since D mesons have an advantage that fragmentation does not modify bare charm quark suppression. For this, we use a theoretical formalism based on energy loss calculations in a finite size dynamical QCD medium [1], which is integrated in a numerical procedure [2] that allows generating predictions with no free parameters used in comparing with the experimental data. The generated predictions have recently shown a robust agreement [3] with various experimental data, which spans across different probes, experiments (RHIC and LHC) and experimental conditions (i.e. all available centrality regions). This model has several key ingredients, such as: i) inclusion of the dynamical scattering centers, ii) inclusion of collisional energy loss, iii) inclusion of running coupling, iv) finite magnetic mass, etc. While all these ingredients are required based on theoretical grounds, it is currently unclear how they individually contribute to the accurate comparison with the experimental data. To that end, we test [4] how accuracy of the predictions is affected by neglecting collisional or radiative energy loss, finite magnetic mass effects and/or effective gluon mass and by using finite coupling constant. We expect that these results will further simplify analysis and interpretation of the underlying experimental results. [1] M. Djordjevic, Phys. Rev. C 80, 064909 (2009). [2] M. Djordjevic and M. Djordjevic, arXiv:1307.4098, PLB in press. [3] M. Djordjevic, M. Djordjevic and B. Blagojevic, arXiv:1405.4250 [4] B. Blagojevic and M. Djordjevic, to be submitted (2014).

Speaker: Ms Bojana Blagojevic (Institute of Physics, University of Belgrade)

Slides HotQuarksTalk_Bojana.pdf HotQuarksTalk_Bojana.pptx

20 Jet quenching and medium excitation in high-energy heavy-ion collisions

Jet quenching has been proposed as a probe of QGP for more than a decade. It is still not clear how does jet loss its energy and how is the lost energy redistributed in the medium. In this talk, medium modification of γ-tagged jets and dijets in high-energy heavy-ion collisions is investigated within a Linearized Boltzmann Transport model for jet propagation that includes both elastic parton scattering and induced gluon emission. Inclusion of recoiled medium partons in the reconstruction of partonic jets is found to significantly reduce the net jet energy loss. Experimental data on γ-jet asymmetry and survival rate in Pb + Pb collisions at √{s}=2.76 TeV can be reproduced. Medium modifications of reconstructed jet fragmentation function, transverse profile and energy flow outside the jet-cone are found to be sizable especially for γ-tagged jets with small values of x=pTjet/pTγ. Medium modification factor of γ-tagged jet and dijets correlations are also studied.

Speaker: Yan Zhu (University of Santiago de Compostela)

Slides HQ14_ZHU.pdf

11:35 Discussion

Session 4: Jets II

Convener: Jana Bielcikova (Acad. of Sciences of the Czech Rep. (CZ))

21 The stringness of heavy ion collisions

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

Slides jcs_stringiness.pdf

22 Renormalization of the jet-quenching parameter

In the context of the recently derived probabilistic picture of in-medium jet evolution, we study radiative corrections which yield potentially large double logarithms, $\alpha_s \ln^2 L$, for large enough medium length $L$.  We show in particular that, due to a large separation of time scales, these corrections can be reabsorbed in a renormalization of the quenching parameter in both the collision rate and radiative rate, preserving the probabilistic picture.  As a major consequence of this analysis, the new renormalized jet-quenching parameter is enhanced compared to the standard perturbative estimate. This yields in particular an increase of radiative energy loss of a fast parton traversing a QCD medium, which scales as $L^{2+\gamma}$ where the anomalous dimension $\gamma=2\sqrt{ \alpha_sN_c/\pi}$, as compared to the standard estimate that yields a scaling in $L^2$. References: arXiv:1311.5823 [hep-ph] (To appear in JHEP), arXiv:1403.2323 [hep-ph] (To appear in NPA)

Speaker: Dr Yacine Mehtar-Tani (IPhT)

Slides HQ14-Yacine.pdf

23 Production of strange particles in charged jets in Pb--Pb and p--Pb collisions measured with ALICE

Properties of the hot and dense strongly interacting matter created in ultra-relativistic heavy-ion collisions can be studied using jets. Hadronisation processes occurring in jets are expected to be modified by the interaction of partons with the medium. At intermediate $p_\textrm{T}$, a~strong increase of the baryon-to-meson ratio is observed for inclusive light particles produced in heavy-ion collisions when compared to the ratio measured in proton--proton collisions. Production by fragmentation cannot explain this phenomenon. Other hadronisation mechanisms, like coalescence or parton recombination, have been proposed instead. Measurements of spectra of identified particles produced in jets in heavy-ion collisions can provide further important insights into the interplay of various hadronisation processes which participate in the particle production in the hot and dense medium. In this contribution, we present the measurements of the $p_\textrm{T}$~spectra of $\Lambda$~baryons and $\textrm{K}^0_\textrm{S}$~mesons produced in association with charged jets in Pb--Pb collisions at $\sqrt{s_\textrm{NN}}=2.76\:\textrm{TeV}$ and in p--Pb collisions at $\sqrt{s_\textrm{NN}}=5.02\:\textrm{TeV}$. The results are obtained with ALICE at the LHC, exploiting the excellent particle identification capabilities of this experiment. Baryon-to-meson ratios of the spectra of strange particles associated with jets are studied in central collisions and are compared to the ratios obtained for inclusive particles and for particles coming from the underlying event.

Speaker: Vit Kucera (Acad. of Sciences of the Czech Rep. (CZ))

Paper proceedings-11-review-3.pdf

Slides 2014-09-23_Hot-Quarks-4.pdf

18:15 break

24 From light- to heavy-quark fragmentation in jets: current measurements in pp collisions with the ALICE detector and perspectives

Measurements of jet fragmentation in heavy-ion collisions are important for investigating the medium-induced parton energy loss. Partons propagating in a dense and strongly interacting medium lose energy giving rise to a softening of the final hadron pT-differential spectrum. The presence of the strongly interacting medium may also lead to particle dependent modifications of the fragmentation function. In particular measurements of the fragmentation of heavy charm and beauty quarks are expected to play a key role. Heavy quarks are an ideal probe of the in-medium energy loss, thanks to their short formation time and their small probability of thermal production from the medium. Their energy loss is expected to be smaller than that of light quarks and this affects also their fragmentation. In order to quantify the medium effects on jet fragmentation, baseline measurements in elementary collisions such as e+e- or pp are needed. These measurement are also important on their own as they test and could further constrain theoretical predictions. Although in the last year significant improvements have been made in NLO QCD parametrizations of fragmentation functions, pp collisions have e.g. different sensitivity to gluon-to-hadron fragmentation with respect to e+e- or ep collisions. In addition, measurements of particle-dependent fragmentation in elementary collisions are not well explored in general. In this talk we will present results on jet fragmentation into charged hadrons, pions, kaons, and protons in pp collisions at sqrt(s) = 7 TeV measured with the ALICE detector. The results will be compared to Monte Carlo generators. In addition, simulation studies and perspectives for the charm fragmentation function measurement will be outlined.

Speaker: Chiara Bianchin (University of Utrecht (NL))

Slides jetFragmentation.pdf

25 Thermodynamic and transport properties of finite temperature and chemical potential strongly coupled quark gluon plasma

The transport properties (shear and bulk viscosities, electric and heat conductivities, etc) of the strongly coupled quark gluon plasma (sQGP) are computed at finite temperature and chemical potential. The cross sections for quark ($q$), anti-quark ($\bar{q}$) and gluon ($g$) elastic scattering at finite temperature and chemical potential, used in our study, are evaluated for dynamical quasi-particles (massive off-shell particles as described by the dynamical quasi-particles model “DQPM” [1]) using the leading order Born diagrams [2]. Within our study, we demonstrate the influence of the finite masse and width of the quasi-particles on the thermodynamic and transport properties of the sQGP. We, furthermore, provide a comprehensive comparison between different models such as the Nambu-Jona-Lasinio (NJL) model and the dynamical quasi-particle model (DQPM) at finite temperature and confront these results with lattice QCD data whenever available [3, 4]. Our results at finite chemical potential constitute a first step for transport approaches aiming to study the QGP at FAIR/NICA experiments [4]. [1] W. Cassing, Eur. Phys. J. Spec. Top. 168, 3 (2009) [2] H. Berrehrah, E. Bratkovskaya, W. Cassing, P.B. Gossiaux, J. Aichelin, and M. Bleicher, Phys.Rev. C89, 054901 (2014). [3] R. Marty, E. Bratkovskaya, W. Cassing, J. Aichelin and H. Berrehrah, Phys. Rev. C88 (2013) 045204 [4] H. Berrehrah, E. Bratkovskaya, W. Cassing, and R. Marty, to be submitted.

Speaker: Dr Hamza Berrehrah (FIAS)

26 Heavy flavours in nucleus-nucleus collisions: quenching, flow and correlations

We present results for the quenching, elliptic flow and azimuthal correlations of heavy flavours in high-energy nucleus-nucleus collisions obtained through the POWLANG transport setup, developed in the past to study the propagation of heavy quarks in the Quark-Gluon Plasma and here extended to include a modeling of their hadronization in the presence of a medium. Hadronization is described as occurring via the fragmentation of strings with endpoints given by the heavy (anti-)quark Q/Qbar and a thermal parton qbar/q from the medium. The flow of the light quarks is shown to affect significantly the R_AA and v_2 of the final D mesons, leading to a better agreement with the experimental data. The approach allows also predictions for the angular correlation between heavy-flavour hadrons (or their decay electrons) and the charged particles produced in the fragmentation of the heavy quark strings.

Speaker: Dr Andrea Beraudo (INFN (Torino))

Slides beraudo.pdf

19:40 More discussions

Wednesday 24 September

Session 5: Flow and correlations I

Convener: Hannah Petersen

27 Overview of the initial state flucuations and final state collectivity

Speaker: Dr Bjoern Schenke (Brookhaven National Lab)

Slides schenke_HotQuarks2014.pdf

28 Identified charged hadron production in Pb-Pb collisions with event shape engineering

Strong event-by-event fluctuations in the energy density of heavy-ion collisions have been recently observed with ALICE, with the measurement of non-zero odd harmonic anisotropic flow coefficients. This measurement suggests the possibility to select different event shapes for a definite centrality and colliding system. The event selection is based on the azimuthal distribution of produced particles (using the so-called “q-vector”). For such shape selected events, the elliptic flow coefficient (v2) is significantly different with respect to the unbiased events. Moreover, recent Monte-Carlo simulations show a strong correlation between the (final state) event shape selection and the (initial state) eccentricity of the collision. This opens the opportunity to characterize events according to the initial geometry. An approach to select the eccentricity of the event with the Event Shape Engineering (ESE) will be here presented. Then the effect of this selection on identified particle spectra, mean transverse momentum and v2 of charged particles in heavy-ion collisions at 2.76 TeV center-of-mass energy will be discussed.

Speaker: Marco-Antonio Tangaro (Universita e INFN (IT))

Slides HQ2014_tangaro.pdf

29 Source eccentricity at freeze-out measured by HBT interferometry with the event shape selection

The higher order flow anisotropies (v_{n}) are considered to be originated from initial geometrical fluctuation of participating nucleons followed by the collective expansion of the hot and dense medium created in high-energy heavy-ion collisions. The source geometry with possible fluctuation at the end of the expansion would depend on the magnitude of the initial fluctuation, the strength of the expansion, the expansion time and the viscosity of the medium. The higher order final spatial anisotropies (\varepsilon_{n}) can be accessible by Hanbury Brown and Twiss (HBT) interferometry with respect to higher order event planes (\Psi_{n}), which is expected to reflect the geometrical size and shape at the end of the freeze-out. We examine the correlation between magnitude of v_{2} and magnitude of \varepsilon_{2} by selecting the magnitude of flow-vector which defines the 2nd order event plane (\Psi_{2}) and by looking at the \Psi_{2} dependence of HBT parameters. Recent result on it from PHENIX will be presented and discussed.

Speaker: Takafumi Niida (University of Tsukuba (JP))

Slides HQ2014_niida_v3.pdf

30 Probing novel long-range correlation phenomena in pPb collisions with identified particles 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. To further investigate the origin of this phenomenon, studies of two-particle correlations with identified $K^0_s$ and Lambda trigger particles in 5.02 TeV pPb collisions are presented, and compared to PbPb collisions over a similar multiplicity range. The $K^0_s$ and Lambdas are cleanly reconstructed via their secondary decay vertices over a wide pseudorapidity and transverse momentum range. The second-order ($v_2$) and third-order ($v_3$) anisotropy harmonics of $K^0_s$ and Lambda are extracted from long-range correlations as a function of particle multiplicity and $p_T$. The wide $p_T$ coverage and rich sample of high multiplicity pPb events allow: (1) a precise examination of the mass ordering effect of $v_n$ at low $p_T$ as predicted by hydrodynamics for a collectively expanding medium; (2) exploration of possible constituent quark number scaling of $v_2$ and $v_3$ between mesons and baryons as was observed in high-energy nucleus-nucleus collisions.

Speaker: Zhenyu Chen (Rice University (US))

Slides HotQuarks2014_Zhenyu.pdf

10:05 Coffee break

31 Directed flow in relativistic heavy-ion collisions within PHSD transport approach and 3FD hydrodynamical model

We analyze recent STAR data for the directed flow of protons, antiprotons and charged pions obtained within the beam energy scan program within the Parton-Hadron-String-Dynamics (PHSD) transport model and a 3-Fluid hydroDynamics (3FD) approach. We clarify the role of partonic degrees of freedom in the the kinetic PHSD approach. The PHSD results, simulating a partonic phase and its coexistence with a hadronic one, are roughly consistent with data. The hydrodynamic results are obtained for two Equation of States (EoS), a pure hadronic EoS and an EoS with a crossover type transition. The latter case is favored by the STAR experimental data. Special attention is paid to the description of antiproton directed flow based on the balance of p-pbar annihilation and the inverse processes for p-bar pair creation from multi-meson interactions. Generally, the semi-qualitative agreement between the measured data and model results supports the idea of a crossover type of quark-hadron transition which softens the nuclear EoS.

Speaker: Dr Volodymyr Konchakovski (Institute for Theoretical Physics, Giessen University)

Slides Konchakovski.pdf

32 Projection method and new formulation of leading-order anisotropic hydrodynamics

Successful applications of relativistic viscous hydrodynamics in the description of heavy-ion collisions at RHIC and the LHC triggered large interest in the development of the hydrodynamic framework. An example of the new approach to relativistic dissipative hydrodynamics is anisotropic hydrodynamics --- the framework where effects connected with the expected high pressure anisotropy of the produced matter are included in the leading order of the hydrodynamic expansion. Very recently, also the second order anisotropic hydrodynamics has been formulated in [1]. The new approach introduced in [1] allows for description of arbitrary transverse expansion of matter in the way which becomes consistent with more traditional approaches to dissipative hydrodynamics in the small anisotropy limit. This formalism uses, however, the Romatschke-Strickland form [2] of the distribution function in the leading order, which implies that the two components of pressure in the transverse plane may be different only if the second-order corrections are taken into account. In this work we present a new methodology for including three substantially different pressure components already in the leading order of hydrodynamic expansion. Our approach is based on the projection method introduced in [3], which has turned out to be a convenient tool to replace complicated tensor equations of relativistic hydrodynamics by a small set of scalar equations. We take into account the radial expansion of the produced matter (in addition to the longitudinal Bjorken flow) but our considerations are confined to the case with cylindrical symmetry. We generalize the Romatschke-Strickland form to the case where all three pressure components may be different. Compared to earlier works on anisotropic hydrodynamics in the leading order, where the zeroth and first moments of the Boltzmann equation have been studied, an important novel feature of our present work is the analysis of the second moment of the Boltzmann equation. We argue that a successful agreement with the Israel-Stewart theory in the limit of small anisotropies may be achieved if we take into account two equations constructed from the second moment of the Boltzmann equation rather than taking one equation from the zeroth moment and another equation from the second moment [4-5]. [1] D. Bazow, U. Heinz, and M. Strickland, arXiv:1311.6720. [2] P.Romatschke and M.~Strickland, Phys. Rev. D 68 (2003) 036004. [3] W. Florkowski and R. Ryblewski, Phys. Rev. C 85 (2012) 044902. [4] L. Tinti and W. Florkowski, Phys. Rev. C 89 (2014) 034907. [5] W. Florkowski, R. Ryblewski, M. Strickland, and L. Tinti, Phys. Rev. C 89 (2014) 054909.

Speaker: Leonardo Tinti (Jan Kochanowski University)

Slides Tinti_HQ2014.pdf

33 A new schock capturing numerical scheme for ideal hydrodynamics

We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with exact solution of Riemann problem with an arbitrary equation of state. Standard numerical tests are executed, such as sound wave propagation and schock tube problem. Low numerical viscosity and high precision are attained with proper discretization.

Speaker: Zuzana Feckova

Slides hq_feckova.pdf

11:35 Discussion

Session 6: Flow and correlations II

Convener: Jana Bielcikova (Acad. of Sciences of the Czech Rep. (CZ))

34 Exact solution of the (0+1)-dimensional Boltzmann equation for a massive gas

We solve the one-dimensional boost-invariant kinetic equation for a relativistic massive system with the collision term treated in the relaxation time approximation. The result is an exact integral equation which can be solved numerically by the method of iteration to arbitrary precision. We compare predictions for the shear and bulk viscosities of a massive system with those obtained from the exact solution. Finally, we compare the time evolution of the bulk pressure obtained from our exact solution with results obtained from the dynamical equations of second-order viscous hydrodynamics. DOI: 10.1103/PhysRevC.89.054908

Speaker: Ewa Maksymiuk (Jan Kochanowski University)

Slides Maksymiuk_Hot_quarks_2014.pdf

35 Shear Viscosity and Electric Conductivity of QGP in a Kinetic Theory Approach

The study of transport coefficients of strongly interacting matter has generated a great interest in the research for Quark-Gluon Plasma (QGP) in Heavy Ion Collisions at relativistic energy. In this work we compute shear viscosity and electric conductivity of QGP exploring a quasiparticle model settled to correctly account for the thermodynamics of Lattice QCD. We compare Relaxation Time Approximation analytic formulas with results obtained solving numerically Relativistic Boltzmann Equation. Quasiparticle model predicts $4\pi\, \eta/s \sim 5$ at the critical temperature $T_c$. However, rescaling the cross-section in order to reproduce the minimum value of $\eta/s=0.08$, it is possible to describe simultaneously recent Lattice results on electric conductivity. Another interesting quantity is the shear viscosity to electric conductivity ratio which could give us information about the quark to gluon scattering rates or relaxation times $\tau_g / \tau_q$.

Speaker: Armando Puglisi

Slides HQ_PUGLISI_Armando.pdf

36 Bulk viscous evolution within anisotropic hydrodynamics

Experimental and theoretical studies of relativistic heavy-ion collisions showed that the behavior of matter produced in such collisions is very well described within viscous hydrodynamic models. However, due to rapid longitudinal expansion in the early stages of evolution of matter the studied system undergoes substantial pressure anisotropies, which often may lead to unphysical results. In order to more accurately treat systems that can possess potentially large pressure anisotropies, a new approach called anisotropic hydrodynamics was developed recently. Here we address an open issue in anisotropic hydrodynamics concerning how to describe systems of massive particles within this framework. For this purpose at first we solve exactly one-dimensional boost-invariant Boltzmann kinetic equation for a relativistic massive system of partons with the collision term treated in the relaxation time approximation. Using exact solutions we are able to numerically establish correct forms of the kinetic coefficients of a massive system. Subsequently, we compare the proper-time evolution of the bulk viscous pressure obtained from the exact solution with results obtained from the dynamical equations of second-order viscous hydrodynamics and leading-order anisotropic hydrodynamics. In the latter case we use recently derived system of moment-based dynamical equations that describe the proper-time evolution of a transversally homogeneous massive gas undergoing boost-invariant longitudinal expansion including the effect of bulk viscosity explicitly. We show that none of the standard viscous hydrodynamics formulations seems to accurately describe the early-time evolution of the bulk viscous pressure. These results indicate that there may be something incomplete in the manner in which 2nd order viscous hydrodynamics treats the bulk pressure. We also show that the inclusion of the bulk degree of freedom highly improve agreement between anisotropic hydrodynamics and the exact solution for a massive gass. Presented work is mainly based on: 1. W.Florkowski, E. Maksymiuk, R.Ryblewski, M.Strickland, arXiv:1402.7348 (accepted for PRC) 2. W.Florkowski, R.Ryblewski, M.Strickland, L.Tinti, arXiv:1403.1223 (accepted for PRC) 3. M.Nopoush, M.Strickland, R.Ryblewski, arXiv:1405:1355 (submitted to PRC)

Speaker: Dr Radoslaw Ryblewski (Kent State University / Institute of Nuclear Physics PAS)

Slides ryblewski.pdf

18:00 Coffee break

37 Pion-kaon femtoscopy in Au+Au collisions at STAR

Femtoscopy analysis allows us to extract information about the properties of source emitting particles of different types. From "classical analysis" of two correlated pions one can calculated source sizes, however, from the non-identical particle correlations, e.g. pion-kaon femtoscopy, one can obtain information not only about source size but about asymmetry in emission processes of pions and kaons as well. Such asymmetry gives knowledge of which type of particles is emitted first/second and/or from which region of the source. The studies of non-identical particle femtoscopy for different collision energies gives us the opportunity, to study how the source size and asymmetry in particle emission depend on the initial conditions of the collision. In this talk, we will present STAR results of pion-kaon femtoscopy at mid-rapidity in Au+Au collisions from Beam Energy Scan program.

Speaker: Ms Katarzyna Poniatowska (Warsaw University of Technology)

Slides HotQuarks2014-Poniatowska.pdf

38 Identified light-flavour particle production measured with ALICE at the LHC as a probe of soft QCD and hot hadronic matter

ALICE is a general-purpose heavy-ion experiment able to identify particles over a wide momentum range thanks to its excellent vertexing and tracking performance, its low material budget and its possibility to combine different Particle IDentification (PID) techniques. In this talk the transverse momentum ($p_{\rm{T}}$) spectra of identified light flavour particles in pp and Pb-Pb collisions and the comparison with models are reported. These spectra are of fundamental importance to study the particle production mechanisms playing a role in the different momentum ranges and probe the hot medium formed in heavy-ion collisions. Further information on the effects of the medium produced in Pb-Pb collisions on particle production can be obtained comparing the particle ratios in the two colliding systems and studying the nuclear modification factor ($R_{\rm{AA}}$) that are also reported in this talk. Finally the pT integrated yields and ratios are discussed in terms of thermal models to extract the properties of the medium produced in Pb-Pb collisions at the chemical freeze-out.

Speaker: Barbara Guerzoni (Universita e INFN (IT))

Slides HQ_2014_Guerzoni.pdf

39 Study of azimuthal correlations between D mesons and charged particles with the ALICE experiment

The main goal of the ALICE experiment is to investigate the properties of the strongly interacting matter formed in heavy-ion collisions, where a Quark-Gluon Plasma (QGP) is produced. Heavy quarks (charm and beauty) are excellent probes to study this state of matter. Due to their large masses these quarks are produced in hard partonic scattering processes in the initial stages of the collision before the QGP is formed. While traversing the medium they experience the full evolution of the QGP and interact with it. ALICE measured a significant suppression of D-meson production in a wide momentum range in central Pb-Pb collisions with respect to the expectation based on the cross section measured in pp collisions, scaled by the number of nucleon-nucleon collisions. This effect is interpreted in terms of the energy loss of charm quarks while traversing the medium. Further insight into the mechanisms through which charm quarks lose energy can be obtained by studying the angular correlations between charmed mesons and charged hadrons produced in pp, p-Pb and Pb-Pb collisions. The comparison of the angular correlation distributions can indeed help to spot possible modifications of the charm quark hadronization induced by the presence of the medium. In addition, the analysis of pp and p-Pb data and the comparison with predictions from Monte Carlo simulations, besides constituting a reference for the interpretation of Pb-Pb data, can provide relevant information on charm production and fragmentation processes. Furthermore, the presence of cold nuclear matter effects could affect the charm production and hadronization. This should be reflected by differences between the results obtained in pp and p-Pb collisions, since cold nuclear matter effects are not present in pp collisions. We will present a study of azimuthal correlations between D$^0$, D$^+$, and D$^{*+}$ mesons and charged hadrons in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. D mesons were reconstructed from their hadronic decays at central rapidity in the transverse momentum range 3 ≤ $p_{\rm T}$ ≤ 16 GeV/$c$ and they were correlated to charged particles reconstructed in the pseudorapidity range |η|<0.8. Perspectives for the measurement in Pb-Pb collisions at √sNN = 2.76 TeV after the ALICE upgrade will be presented as well.

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

Slides Colamaria_-_Hot_Quarks_2014.pdf

19:30 More discussions

Thursday 25 September

Session 7: Beam energy scan

Convener: Hannah Petersen

40 Overview of the BES results

Speaker: Dr Marlene Nahrgang

Slides talk_marleneHQ2014.pdf

41 Beam energy scan using a 3+1D viscous hydro+cascade model

Following the BES program at BNL RHIC, we perform a similar collision energy scan using a 3+1D viscous hydrodynamics coupled to the UrQMD hadron cascade. We study how the collision energy affects the bulk observables: rapidity distributions and $m_T$-spectra of identified particles, elliptic, triangular flow and HBT radii, including azimuthally-sensitive HBT. In our calculations we use an equation of state for finite baryon density and averaged or event-by-event initial conditions from UrQMD. We show how the final observables are sensitive to the initial state fluctuations and its granularity, as well as to the shear viscosity in the hydrodynamic stage. We also discuss the constraints on the model parameters imposed by the experimental data.

Speaker: Iurii Karpenko (Frankfurt Institute for Advanced Studies)

Slides hq2014.pdf

42 Higher order fluctuations of conserved charges in heavy ion collisions

We investigate the effects of the global charge conservation on the rapidity window dependences of fluctuations of conserved charges observed in heavy ion collisions by solving the diffusion master equation with boundaries. Our result suggests that the effect of the global charge conservation for the diffusion in the hadronic phase is negligible in the experimental results even with the largest rapidity window acceptance at ALICE. The rapidity window dependences of the fluctuations of conserved charges contain various information on the matter generated in heavy ion collisions such as diffusion constant in the hadronic phase.

Speaker: Miki Sakaida (J)

Slides hotquarks2014_sakaida.pdf

43 Determination of freeze-out conditions from fluctuation observables measured at RHIC

Fluctuations in the conserved charges of the strong interaction are important probes in high-energy heavy-ion collisions, which provide an excellent opportunity for revealing details in the phase structure of QCD matter. Recently, net-electric charge and net-proton fluctuations measured in the beam energy scan program at RHIC were reported by the STAR collaboration. In this talk, we present a new freeze-out curve, which is determined from a combined fit to these fluctuation observables within a phenomenological approach based on the hadron resonance gas model. We also point out that net-strangeness fluctuations may indicate a separate freeze-out behavior of strange hadrons. For a realistic description, we apply the relevant kinematic cuts and systematically include final state effects such as resonance decays and regenerations. The inclusion of the successive regeneration and decay of resonances turns out to be crucial for reconciling calculations of net-proton fluctuations with those of net-baryon number fluctuations and for obtaining reasonable freeze-out conditions.

Speaker: Dr Marcus Bluhm (North Carolina State University)

Slides HQ2014Bluhm.pdf

10:05 Coffee break

44 Recent results on event-by-event fluctuations in ALICE at LHC

Non-statistical event-by-event fluctuations in relativistic heavy ion collisions have been proposed as probe of phase instabilities near the QCD phase transition. In a thermodynamical picture of the strongly interacting system formed in heavy-ion collisions, the fluctuations of the mean transverse momentum, mean multiplicity, balance function, net-particle higher moments etc. are related to the fundamental properties of the system, hence they may reveal information about the QCD phase transition. In this presentation, we will discuss the recent results on event-by-event measurements at LHC energies. We will also make comparisons to the lower energy measurements, and discuss the status and prospects for the higher moment studies at ALICE.

Speaker: Satyajit Jena (University of Houston (US))

Slides 20140925-SJ-HotQuark.pdf

45 Charge dependence of identified two-hadron correlation relative to the reaction plane in Pb-Pb collisions measured with ALICE

Recently a non-zero charge dependence of two-particle correlation relative to the reaction plane in relativistic heavy-ion collisions was observed by RHIC and LHC experiments. The interpretation of these results is a hot topic of debate in the heavy-ion community because of its possible implication for our understanding of parity violation in strong interactions. We extend the ALICE measurement of the charge dependent two-particle correlations in Pb-Pb collisions at $\sqrt{s_{NN}}=~$2.76 TeV with one identified hadron (pion, kaon, or proton). Correlations are reported as a function of the identified hadron transverse momentum. These new results are important for disentangling contributions from a number of competing physics effects, such as local charge conservation coupled with strong anisotropic flow, flow fluctuations, and possible contribution from parity violation coupled with strong magnetic fields, the so-called chiral magnetic effect.

Speaker: Jacobus Onderwaater (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

Slides ChargeDependentCorrelations_JaapOnderwaater_v6.pdf

11:15 Discussions

Excursion: Alhambra with visit to Nazari Palaces

Friday 26 September

Session 9: Heavy Flavour

Convener: Raphael Granier De Cassagnac (Ecole Polytechnique (FR))

46 Future of HI

Speaker: Cyrille Marquet (CPHT - Ecole Polytechnique)

Slides hq14.ppt

47 Overview of heavy flavor measurements

Heavy quarks are produced early in the heavy-ion collisions and they are expected to interact differently from light quarks with the Quark Gluon Plasma (QGP); therefore, they are unique probes of the QGP properties. Their production and elliptic flow are sensitive to the medium dynamics. These measurements for open heavy flavor sector are crucial for understanding the parton energy loss mechanism and the degree of thermalization of the QGP and to determine the transport coefficients of the QGP. Moreover, production of various quarkonia states can provide insight into thermodynamic properties of the QGP since different states are predicted to disassociate (due to the Debye screening of the quark-antiquark potential) at different temperatures. In this talk, I review recent measurement of heavy flavor production in A+A and p+A collisions at RHIC and LHC. I discuss physics implications of these results and near-future prospects for heavy flavor physics.

Speaker: Mr Daniel Kikola (Warsaw University of Technology)

Slides HQ2014_HeavyFlavor.pdf

48 Measurement of electrons from charm and beauty-hadron decays in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE at the LHC

The characterisation of the Quark-Gluon Plasma (QGP), the deconfined state of strongly-interacting matter produced in high-energy heavy-ion collisions, is the main purpose of ALICE at the LHC. The medium can be probed by charm and beauty quarks since they are produced in initial hard partonic interactions and experience its complete evolution. The transverse momentum, $p_{\rm T}$, distribution of heavy-flavour hadrons and of their decay leptons is an observable sensitive to the energy loss of heavy quarks in the hot and dense medium. In addition to the QGP, the presence of cold nuclear matter in the initial state may affect the production of heavy-flavour hadrons. In p-Pb collision no medium creation is expected and thus initial state effects on the heavy-flavour production can be studied in detail. Using the excellent tracking and electron identification capabilities of ALICE, it is possible to measure electrons from heavy-flavour hadron decays over a wide momentum range. By taking advantage of the excellent resolution of the silicon vertex detectors, electrons from charm and beauty hadron decays can be discriminated based on their displacement from the interaction vertex. The $p_{\rm T}$-differential production cross section of electrons from heavy-flavour hadron decays measured in the rapidity range $-1.06 < y_{\rm CMS} < 0.14$ in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented. The cross section of electrons from beauty-hadron decays, isolated based on their larger average displacement from the interaction vertex, will be discussed as well. The nuclear modification factor $R_{\rm pPb}$ of heavy-flavour and beauty decay electrons will be shown. Theoretical predictions including the effects due to the nuclear modification of the parton distribution functions will be discussed with the results.

Speaker: Jan Wagner (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))

Slides jwagnerHQ14_v5.pdf

10:00 Coffee break

49 Study of strange mesons in $p$+$p$, $d$+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV

Strange hadrons are among the most interesting probes of the quark-gluon-plasma, created in the collisions of heavy ions at relativistic energy. The PHENIX experiment at RHIC has measured invariant transverse momentum spectra and nuclear modification factor ($R_{AA}$) of strange mesons K^{*0} and K^{0}_{S}, in $p$+$p$, $d$+Au and Cu+Cu collisions at center of mass energy 200 GeV. The transverse momentum range of these measurements spans from 1.1 to 8.5 GeV/c for $K^{*0}$ and from 2 to 13 GeV/c for $K^{0}_{S}$. Similar to the other light-quark mesons measurements, both these strange mesons show no cold-nuclear-matter effects in the measured $p_T$ range in $d$+Au collisions. The nuclear modification factor ($R_{dAu}$) $\approx$ 1 and is almost constant as a function of $p_{T}$. It is interesting to have the quantitative study of ($R_{CuCu}$) of the strange mesons ($K^{*0}$, $K^{0}_{S}$) in heavy ion collisions as a function of centrality. In case of peripheral collisions, no suppression is registered with respect to the $p$+$p$ yields scaled with number of binary collisions. Where as in central collisions, both mesons suffer substantial amount of suppression at high $p_T$ ($>$ 5 GeV/c), which is similar to the suppression suffered by light-quark mesons. In the intermediate $p_T$ range (2 $<$ $p_T$ $<$ 5 (GeV/c)), the strange mesons are less suppressed than the light-quark meson ($\pi^{0}$) and more suppressed than the baryons ($p$, $\bar{p}$).

Speaker: Mrs Priyanka Sett (Bhabha Atomic Research Center)

Slides Priyanka.pdf

50 Non-Photonic Electron Measurement With STAR Experiment

Non-Photonic Electron Measurement With STAR Experiment Olga Rusňáková (for the STAR Collaboration) Heavy quarks, primarily produced in initial hard scattering processes at the Relativistic Heavy Ion Collider (RHIC), are important tools for understanding the properties of the Quark-Gluon Plasma (QGP). The heavy quark interaction with the QGP can be studied through non-photonic electrons (NPE), which are produced from semi-leptonic decays of heavy flavor hadrons. In p+p collisions measurements of heavy flavor production serve as a test of the pQCD framework and are used as a baseline in comparison with measurements in heavy ion collisions. In Au+Au and $d$+Au the hot and cold nuclear matter effects can be quantified through the nuclear modification factors ($R_{AA}$, $R_{dA}$). The energy dependence of $R_{AA}$ and elliptic flow $v_2$ can be used to further probe the interaction between heavy quarks and the medium. In this talk, we will present a new measurement of NPE production in p+p collisions at $\sqrt{s}$=200 GeV in a broad transverse momentum range of 0.5 - 8 GeV/c. We will discuss the energy dependence of NPE production and azimuthal anisotropy measurements in Au+Au collisions at $\sqrt{s_{NN}}$=39, 62.4 and 200 GeV. Nuclear modification factors $R_{AA}$ in Au+Au collisions and $R_{dA}$ in $d$+Au collisions at $\sqrt{s_{NN}}$=200 GeV will be presented too.

Speaker: Ms Olga Rusňáková (CTU Prague)

Slides Olga.pdf

51 Measurement of beauty-hadron decay electrons in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76 \textrm{TeV}$ with ALICE

The ALICE Collaboration at the LHC studies nucleus-nucleus collisions with the aim of investigating the properties of the high energy-density state of strongly-interacting matter produced in heavy-ion collisions, the Quark Gluon Plasma (QGP). Heavy quarks (charm and beauty) are an effective probe to investigate the properties of the QGP. They are produced almost exclusively in the initial partonic scattering processes and they interact strongly with the surrounding matter throughout its evolution losing energy via elastic and inelastic interactions with the medium constituents. The in-medium parton energy loss is expected to depend both on the parton mass and its colour charge making flavour-separated measurements of charm and beauty useful to test models of in-medium energy loss. Experimentally one way to study heavy quarks is via measurements of electrons from semileptonic decays of heavy-flavour hadrons. The comparison of the $p_{\textrm{T}}$-differential invariant yields of heavy-flavour decay electrons in pp and Pb-Pb collisions gives insight into the energy loss of heavy quarks in the QGP. Electrons are reconstructed in the central rapidity region and identified using the excellent particle identification capabilities of ALICE. To achieve a flavour-separated measurement, additional information is necessary. This separation is done statistically based on the impact parameter of tracks identified as electrons. The absolute value of the impact parameter is typically larger for electrons originating from the decay of hadrons containing a beauty quark due to their larger mean proper decay length ($c\tau\approx500\mathrm{\mu m}$) compared to other hadrons decaying into electrons. In this talk the measurement of the beauty decay electrons is presented for pp collisions at $\sqrt{s}=7 \textrm{TeV}$ and for Pb-Pb collisions at $\sqrt{s_{NN}}=2.76 \mathrm{TeV}$ and both are compared via the nuclear modification factor. The latter describes the change in the $p_{\textrm{T}}$-differential cross-section in Pb-Pb collisions compared nucleon-nucleon collisions in a vacuum - adequately normalized to the average number of nucleon-nucleon collisions in a given centrality class and it is thus sensitive to the in-medium energy loss of partons.

Speaker: Martin Andreas Volkl (Ruprecht-Karls-Universitaet Heidelberg (DE))

Slides Martin.pdf

11:30 Discussion

Session 10: Photons & Dileptons

Convener: Rainer Fries (Texas A&M University)

52 Multiplicity dependence of transverse momentum correlations in p-Pb at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV and Pb-Pb at $\sqrt{s_{\mathrm{NN}}}=$ at 2.76 TeV

Two-particle correlations provide information about particle production mechanisms in heavy-ion collisions. We report on the study of two particle transverse momentum correlations ($\Delta p_{\rm T} \Delta p_{\rm T}$) in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV measured with the ALICE detector at LHC. Unlike the number correlation functions, $\Delta p_{\rm T} \Delta p_{\rm T}$ measures transverse momentum correlations between particle pairs. The $p_{\rm T}$ dependence of this correlation measure may make it amenable to probe the fluctuations in temperature, average momentum, flow, hardness of spectrum and hardness of correlations (jet vs non-jets). Correlation functions for $++$, $+-$, and $--$ charged particle pairs as a function of pair azimuthal and pseudo-rapidity separation are measured. We study their evolution with collision centrality and particle multiplicity per event. We find that $\Delta p_{\rm T} \Delta p_{\rm T}$ correlation shapes exhibit a strong centrality dependence in Pb-Pb collisions and multiplicity dependence in p-Pb collisions. The correlation function is everywhere positive, indicating that both particles from a pair are more likely to have momentum above or below the average transverse momentum in an event ensemble. We further study the Fourier decomposition of the correlation function dependence on $\Delta \varphi$ as a function of $\Delta \eta$.

Speaker: Dr Prabhat Pujahari (Wayne State University)

Slides

• DptDpt-HQ2014-prp.pdf
• DptDpt-HQ2014-prp-V1.pdf
• Prabhat_HQ2014-dptdpt-prp.pdf

53 Effects of quark chemical equilibration on thermal photon elliptic flow

Large hadronic elliptic flow $v_2$ is an evidence for the existence of a strongly-coupled QGP fluid in high-energy heavy-ion collisions. Since the medium is electromagnetically transparent, thermal photon $v_2$ was speculated to be much smaller than hadronic ones due to the contribution from the earlier stages where azimuthal flow is small. However, it has recently been found to be much larger than hydrodynamic estimations in both RHIC and LHC experiments, which is recognized as "photon $v_2$ puzzle" [1]. In this study, I discuss the implication of late quark chemical equilibration on the thermal photon $v_2$ [2] because the system in transition from a gluon-rich color glass condensate to an equilibrated QGP would have smaller number of quarks at the beginning [3]. The elliptic flow of thermal photons would be enhanced by the chemical imbalance because the photons are emitted from the quarks produced after sizable azimuthal anisotropy has developed in the flow. Numerical analyses with a newly-developed (2+1)-dimensional hydrodynamic model coupled to the rate equations for quark and gluon number changing processes imply that the thermal photon $v_2$ can be visibly enhanced. The mechanism would also lead to large $v_3$ which is revealed in the latest RHIC data. They indicate that interplay of the equilibration processes and the collective expansion would be important in explaining the heavy-ion phenomenon. References: [1] A. Adare et al. [PHENIX Collaboration], Phys. Rev. Lett. 109, 122302 (2012). [2] A. Monnai, arXiv:1403.4225 [nucl-th]. [3] A. Monnai and B. Mueller, arXiv:1403.7310 [hep-ph].

Speaker: Dr Akihiko Monnai (RIKEN BNL Research Center)

Slides hq14_Akihiko_monnai_ver_final.pdf

54 Heat- and Electric Conductivity of the Quark-Gluon Plasma

The study of transport coefficients of the Quark-Gluon Plasma (QGP) provides useful comparisons amongst different theories and models, and gives physical insights into the microscopic details of the QGP. We work with the partonic transport model BAMPS (Z. Xu and C. Greiner, Phys. Rev. C, pp. 1–121, 2005.), solving the relativistic Boltzmann equation for several species of charged partons. BAMPS has implemented elastic and inelastic pQCD scattering routines (O. Fochler, J. Uphoff, Z. Xu, and C. Greiner, Phys. Rev. D, pp. 1–11, 2013.) and allows for a systematic study of the influence of scattering on the transport coefficients. In this study, only static box-simulations of hot quark matter are performed. Via Green-Kubo relations transport coefficients like the electric conductivity or heat conductivity can be explored. Furthermore, we employ the classical picture, evaluating the static diffusion current upon influence of an external electric field. For the heat conductivity, a temperature gradient can be build up and the resulting static heat flow measured (M. Greif, F. Reining, I. Bouras, G. Denicol, Z. Xu, and C. Greiner, Phys. Rev. E, vol. 87, no. 3, p. 033019, Mar. 2013.). We show the equivalence of the Green-Kubo method and the the "textbook-picture"-methods. We give results for these transport coefficients for simple toymodel systems and the more realistic case of a fully inelastically interacting QGP. The electric conductivity of the QGP has been calculated by different lattice groups, Dyson-Schwinger calculations and transport simulations. We compare our results with others. We present different analytical approaches to solve the Boltzmann equation, aiming for transport coefficients of the QGP, and compare them to our numerical results.

Speaker: Mr Moritz Greif (Goethe University Frankfurt)

Slides Moritz_Greif_HotQuarks.pdf

18:30 Coffee break

55 Low mass dimuon production in pp, p-Pb and Pb-Pb collisions with the ALICE muon spectrometer

Low mass 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 (called Quark Gluon Plasma). Strangeness enhancement is one of the possible signatures of the Quark Gluon Plasma formation and can be accessed through the measurement of $\phi$ meson production with respect to $\rho$ and $\omega$ mesons, while the measurement of the $\phi$ nuclear modification factor provides a powerful tool to probe the production dynamics and hadronization process in relativistic heavy ion collisions. We present results on the low mass dimuon analysis in pp, p-Pb and Pb-Pb collisions. In pp collisions at $\sqrt{s}$ = 2.76 TeV the $\phi$ differential cross section as a function of the transverse momentum has been measured. The comparison with PHOJET and the PYTHIA tunes Perugia-0, Perugia-11, ATLAS-CSC and D6T shows that Perugia-0, Perugia-11 and ATLAS-CSC underestimate the data, D6T slightly overestimates them and PHOJET is in good agreement. The $\phi$ yield and the nuclear modification factor $R_{pPb}$ at forward and backward rapidity have been measured in p-Pb collisions at $\sqrt{s}$ = 5.02 TeV. At forward rapidity, $R_{pPb}$ increases as a function of $p_T$, saturating for $p_\mathrm{T} >$ 3 GeV/*c* at $R_{pPb}\sim 1$. At backward rapidity $R_{pPb}$ shows an increase as a function of the transverse momentum up to a factor of 1.6 for $p_T$ $\sim$ 3-4 GeV/*c*, followed by a decrease at higher $p_\mathrm{T}$. The $\phi$ yield and nuclear modification factor $R_{AA}$ have been measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV in the intermediate $p_T$ region 2 $< p_T <$ 5 GeV/*c*, as a function of the number of participating nucleons. Remarkable differences are observed in the comparison between these results and the ones measured in the same $p_\mathrm{T}$ range at midrapidity in the hadronic channel $\phi \rightarrow KK$.

Speaker: Ester Anna Rita Casula (Universita e INFN (IT))

Slides hot_quarks_2014.pdf

56 Low-Mass Dielectron Production in pp, p-Pb and Pb-Pb Collisions with ALICE

The measurement of electron-positron pairs (dielectrons) in the low invariant mass region allows studying the vacuum and in-medium properties of light vector mesons. Additionally, low-mass dielectrons are produced by internal conversion of virtual direct photons. They are excellent direct probes to study all collision stages, since they pass through the created medium almost unaffected. To quantify modifications of the dielectron production in heavy-ion collisions, measurements in pp collisions serve as a reference, while the analysis of p-A collisions allows disentangling cold from hot nuclear matter effects. I will present dielectron measurements from the ALICE experiment at the LHC, where electrons at mid-rapidity are identified by their specific energy loss in the Inner Tracking System (ITS) and the Time Projection Chamber (TPC), combined with time-of-flight information from the TOF detector. The dielectron invariant mass distributions will be compared to the expected hadronic sources in pp collisions at $ \sqrt{s}=7 $ TeV and in p-Pb collisions at $ \sqrt{s_{\rm NN}}=5.02 $ TeV. In addition, the status of the analysis of Pb-Pb collisions at $ \sqrt{s_{\rm NN}}=2.76 $ TeV will be presented. The aim is the extraction of the virtual direct photon yield, which gives access to the temperature of the created medium. Also future prospects of low-mass dielectron measurements with an upgraded ALICE detector after the second LHC long shutdown in 2018 will be discussed.

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

Slides HQ-2014-Reichelt-v5.pdf

57 Dilepton production in transport-based approaches

Lepton pairs are an excellent probe for matter at high densities and temperatures. In particular they provide a rather direct access to the in-medium self energy of vector mesons, which is believed to be dominated by baryonic effects. We perform transport-based simulations with the GiBUU and UrQMD models to investigate dilepton production in a wide energy range and show that baryonic contributions are particularly important at low energies, where they can show up as Dalitz-like channels already in vacuum, but also generate a sizeable in-medium enhancement. In order to incorporate in-medium contributions, we employ a coarse-graining approach, which makes it possible to couple a realistic transport evolution with sophisticated in-medium spectral functions. In this way we achieve a good description of low-mass dilepton spectra at SIS and SPS energies within one consistent framework. This also paves the way for further investigations connected to the RHIC beam energy scan and the future CBM experiment at FAIR.

Speaker: Janus Weil (FIAS)

Slides hq14_weil.pdf

19:50 More discussions

Saturday 27 September

Session 11: resonance, hadronization and Quarkonium

Convener: Boris Hippolyte (Institut Pluridisciplinaire Hubert Curien (FR))

58 Non-extensive Thermodynamical Approach of Hadronization in High-Energy Collisions

Hadron spectra measured in high-energy collisions present distributions which can be derived from the non-extensive statistical and thermodynamical phenomena [1,2]. 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 [3,4]. Here in this talk, I would like to summarize the theoretical background of this approach, then present what can we learn from the recent theoretical and phenomenological developments. Finally will also give the physical interpretations of the parameters can be measured via analysing measured hadron spectra. References: [1] T.S. Biró, G.G. Barnaföldi, P. Ván: Eur.Phys.J. A49 (2013) 110 [2] T.S. Biro, G.G. Barnaföldi, P. Van: arXiv:1405.3813 [3] K. Ürmössy, G.G. Barnaföldi, T.S. Bíro: Phys.Lett. B718 (2012) 125-129 [4] K. Ürmossy, G.G. Barnaföldi, T.S. Bíro: Acta Phys.Polon.Supp. 5 (2012) 363-368

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

Slides GGBarnafoldi_HQ_2014_v2.pdf

59 (Hyper)nuclei and anti-(hyper)nuclei production in Pb--Pb collisions in ALICE at LHC

The ALICE detector at LHC allows to study Pb--Pb collisions at the new energy frontier. At this energy almost equal amounts of matter and antimatter are produced in the central rapidity region. Closely related to this is the production of (hyper)nuclei and anti-(hyper)nuclei, which are measured with nearly similar abundances. Based on its high tracking and particle identification capabilities, the ALICE detector allows to investigate this rarely produced (anti-)matter. The production yields of light nuclei and of the (anti-)hypertriton will be discussed. Further, a search for exotic bound states such as the H-dibaryon ($\rm{\Lambda \Lambda}$) and a possible $\rm{\Lambda n}$ bound state will be presented. The various results will be compared with thermal and coalescence model predictions.

Speaker: Manuel Colocci (Universita e INFN (IT))

Slides Talk_Colocci.pdf

60 Search for Antimatter Muonic Atoms at RHIC

In ultrarelativistic heavy-ion collisions with high particle multiplicities, a muon can be bound to a charged hadron by Coulomb force and form a hydrogen-like atom. Among these atoms, the antimatter muonic hydrogen ($\bar{p}-\mu$) and the $K-\mu$ atom have been predicted but not yet been discovered[1]. At the STAR experiment, muon identification at low transverse momentum provides a great opportunity to search for a variety of muonic atoms. Because only thermal muons or muons from short-lived resonance decays are capable of forming muonic atoms, they can be used as an ideal tool, as suggested by M. Schwartz, J. Sandweiss and the authors of [1,2], to determine the thermal emission from the Quark-Gluon Plasma via a direct measurement of the single muon spectrum. We will present our results on the $\sqrt{s_{NN}}=200$ GeV Au+Au collisions collected by the STAR experiment at RHIC. We will show the possible signatures of the new muonic atoms extracted from invariant mass distributions and also from particle correlations. [1] Joseph Kapusta and Agnes Mocsy, Phys. Rev. C 59, 5, (1999). [2] Gordon Baym, Gerald Friedman, R. J. Hughes and Barbara V. Jacak, Phys. Rev. D 49, 4 (1993).

Speaker: Kefeng Xin

Slides Kefeng_Xin_HQ14.pdf

61 Resonances as Probes of Heavy-Ion Collisions at ALICE

Hadronic resonances serve as unique probes in the study of the hot and dense nuclear matter produced in heavy-ion collisions. The properties of the hadronic phase of the collision (the temperature and lifetime) can be extracted from measurements of the suppression of resonance yields with respect to the yields of stable particles. A comparison of the transverse-momentum spectra of the $\phi(1020)$ meson and the proton (which have similar masses) can be used to study particle production mechanisms in heavy-ion collisions. Resonance measurements in pp collisions provide input for tuning QCD-inspired particle production models and serve as reference measurements to which results from other collision systems can be compared. Measurements of resonance properties in p-Pb collisions allow nuclear effects in the absence of a hot and dense final state to be studied. The ALICE Collaboration has measured resonances in pp, p-Pb, and Pb-Pb collisions. These measurements, including $\it{p}_{\mathrm{T}}$ spectra, masses and widths, mean transverse momenta, ratios to stable particles, and nuclear modification factors will be discussed and compared to results from other experiments and to theoretical models.

Speaker: Anders Garritt Knospe (University of Texas (US))

Slides Anders_Knospe_HQ14.pdf

09:50 Coffee break

62 Multi-strange baryon production in pp, p-Pb and Pb-Pb collisions measured with ALICE

Transverse momentum spectra and yields of charged $\Xi$ and $\Omega$ at mid-rapidity in proton-proton (pp), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions measured in the ALICE experiment at LHC will be presented. These particles are reconstructed via their cascade weak decay topology into charged particles only, using the excellent tracking and particle identification capabilities of the detector. For p-Pb and Pb-Pb, the $\Xi$ and $\Omega$ spectra were also studied as a function of collision centrality. The results will be compared with model predictions. The multi-strange baryon production relative to non-strange particles has been studied for different centralities. The new measurement in p-Pb collisions will act as interface to understand the change in relative strangeness production from pp collisions to Pb-Pb collisions. Furthermore, the nuclear modification factors for the charged $\Xi$ and $\Omega$ particles, compared with those for other light particles, will be shown and discussed.

Speaker: Domenico Colella (Universita e INFN (IT))

Slides Domenico_Colella_HQ14.pdf

63 Bottomonia in pp, pPb and PbPb

Bottomonia are important probes of the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. The three Y states (1S, 2S, 3S) were measured separately using the Compact Muon Solenoid (CMS) experimental apparatus and observed to disappear sequentially in PbPb collisions at 2.76 TeV. However, recent measurements in pp and pPb collisions, at 2.76 and 5.02 TeV respectively, show a surprising dependence of the excited (2S or 3S) over the ground (1S) state ratio, as a function of the global event activity. The three states are also observed to be individually more produced in events with more activity, for the three collision systems. In this talk, we will review the latest results from pp, pPb and PbPb collisions and highlight their possible interpretations.

Speaker: Nicolas Filipovic (Ecole Polytechnique (FR))

Slides Nicolas_Filipovic_HQ14.pdf

64 J/$\psi$ and $\psi(2S)$ measurements in $p$+$p$ collisions at $\sqrt{s}$ = 200 and 500 GeV in the STAR experiment

Barbara Trzeciak for the STAR Collaboration The $J/\psi$ production mechanism in elementary particle collisions is not yet exactly known. For many years measurements of the J/$\psi$ cross-section have been used to test different J/$\psi$ production models. While many models can describe relatively well the experimental data on the J/$\psi$ cross-section in $p+p$ collisions, they have different predictions for the J/$\psi$ polarization. Therefore, measurements of the J/$\psi$ polarization may allow to discriminate among different models and provide new insight into the J/$\psi$ production mechanism. In this talk, results on the J/$\psi$ cross-section at $\sqrt{s}$ = 200 and 500 GeV and the J/$\psi$ polarization at $\sqrt{s}$ = 200 measured via the dielectron decay channel at mid-rapidity in $p+p$ collisions in the STAR experiment will be discussed. We will also report a status of the J/$\psi$ polarization analysis and the first $\psi(2S)$ measurement at $\sqrt{s}$ = 500 GeV. Moreover, prospects of charmonia measurements with the newly upgraded STAR detector will be reported.

Speaker: Barbara Trzeciak (Czech Technical University in Prague)

Slides Barbara_Trzeciak_HQ14.pdf

11:30 Discussion

Session 12: Quarkonium II

Convener: Lijuan Ruan

65 Measurement of $\Upsilon$ in $\mbox{p+p}$ collisions in the STAR experiment

Quarkonium suppression was proposed as a signature of quark-gluon plasma(QGP) formation. Different members of the quarkonia family are expected to melt at different temperatures providing an estimate of the temperature reached in QGP. The $\Upsilon$ states offer a clean probe of QGP. Previous measurements at RHIC focused on colliding system and centrality dependence of $\Upsilon$ nuclear modification factor $\mbox{$R_{\textit{AA}}$}$. The $\Upsilon$ $\mbox{$R_{\textit{AA}}$}$ as a function of $\mbox{$p_T$}$ will provide additional information about its interaction with the QGP, which requires a $\mbox{$p_T$}$ spectrum in $\mbox{p+p}$ as a baseline. Measurement of $\Upsilon$ $\mbox{$p_T$}$ spectrum in $\mbox{p+p}$ collisions at $\sqrt{s}=500$ $\mbox{$\mathrm{GeV}$}$ may provide such a baseline with a high precision. It can be rescaled based on $pQCD$ calculations and used as a baseline for $\mbox{Au+Au}$ collisions at $\sqrt{s_{NN}}=200$ $\mbox{$\mathrm{GeV}$}$. In this presentation, the status of $\Upsilon$ measurements in $\mbox{p+p}$ collisions at $\sqrt{s}=500$ $\mbox{$\mathrm{GeV}$}$ in the STAR experiment will be presented. In addition the future possibilities, thanks to recent upgrades of the STAR detector, will be discussed. With the help of Muon Telescope Detector(MTD) it may be possible to measure $\Upsilon$ 1S,2S and 3S states separately.

Speaker: Leszek Kosarzewski (Warsaw University of Technology)

Slides Upsilon_HQ_2014_LK.pdf

66 $J/\psi$ production in the Statistical Hadronization Model - limitations and implications

Using a Statistical Hadronization Model which includes charmed hadrons and charmonia, we describe thermal $J/\psi$ production on the hadronic as well as the partonic level under the assumption of detailed balance and entropy conservation. We investigate the dependence of the $J/\psi$ multiplicity on the primary model parameters, the freeze-out temperature and the baryochemical potential. We find a very strong dependence on the charm quark mass for the partonic description and discuss the implications for the effective dressed mass of the charm quark.

Speaker: Mr Philipp Bahavar (Goethe University Frankfurt)

Slides Philipp_BahavarHQ14.pdf

67 Inclusive J/ψ production in pp, p-Pb and Pb-Pb collisions at forward rapidity with ALICE at the LHC

The ALICE collaboration has studied inclusive J/$\psi$ production in pp, p-Pb and Pb-Pb collisions with the ALICE Muon Spectrometer. The measurement was performed in the rapidity range 2.5 $<$ $y_{lab}$ $<$ 4.0, studying the decays into muon pairs. The J/$\psi$ production cross-sections in pp at $\sqrt{s}= 7$ TeV, both integrated and differential in rapidity and in transverse momentum will be presented. The J/$\psi$ nuclear modification factor as a function of rapidity or transverse momentum in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV will be presented and compared to theoretical models. A suppression of the J/$\psi$ has been found in Pb-Pb collisions, with respect to the J/$\psi$ measured in pp collisions at the same center-of-mass energy. p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV have also been studied at the LHC, in order to measure the effects related to cold nuclear matter, which, for charmonia, include gluon shadowing (or gluon saturation), energy loss and nuclear absorption. The study of these effects in p-Pb collisions is important in order to be able to disentangle hot and cold nuclear matter effects in Pb-Pb collisions. Results on inclusive J/$\psi$ nuclear modification factor in p-Pb collisions will be presented and compared to theoretical models. Since the LHC provided both p-Pb and Pb-p collisions, forward and backward rapidity region were probed. The implication of these results for the interpretation of Pb-Pb collision results will be discussed.

Speaker: Javier Martin Blanco (Laboratoire de Physique Subatomique et des Technologies Associe)

Slides Javier_MartinBlanco_JPsiProductionInALICE.pdf

18:00 Coffee break

68 Forward rapidity $\psi(\mathrm{2S})$ production in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

The ALICE Collaboration has studied the inclusive $\psi(\mathrm{2S})$ production in pp, p-Pb and Pb-Pb collisions at the CERN LHC. The $\psi(\mathrm{2S})$ is detected through its decay to muon pairs, using the Forward Dimuon Spectrometer, which covers the rapidity range 2.5<$y_{lab}$<4. The $\psi(\mathrm{2S})$ production cross sections in pp collisions will be presented, both integrated and differential in rapidity and in transverse momentum. In p-Pb collisions, $\psi(\mathrm{2S})$ results will be compared to the J/$\psi$ ones by means of the production cross sections ratio studied as a function of the transverse momentum and event activity. The $\psi(\mathrm{2S})$ nuclear modification factor, $R_{pA}$ , will also be presented. The results show a larger $\psi(\mathrm{2S})$ suppression compared to the one observed for the J/$\psi$ and are not described by theoretical models including cold nuclear matter effects as nuclear shadowing and energy loss. Finally, preliminary results on $\psi(\mathrm{2S})$ production in Pb-Pb collisions will be shown in two $p_{T}$ ranges as a function of centrality. Also in this case, the $\psi(\mathrm{2S})$ production will be compared to the J/$\psi$ one and to the corresponding pp results.

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

Slides MarcoLeoncino_HQ14.pdf

69 $J/\psi$ production as a function of charged particle multiplicity in $p+p$ collisions at $\sqrt{s} = 510$ GeV

In a high energy proton-proton collision, more than one inelastic parton-parton interaction can occur, which is described as multiple parton interaction (MPI). Each of the parton interaction would contribute to the overall particle multiplicity, as well as higher probability of producing a $J/\psi$ particle in the collision. Therefore, the MPI scenario can be tested by studying the yield of $J/\psi$ as a function of multiplicity. In addition, such measurement also provides additional information on the $J/\psi$ production mechanism, which is still not fully understood. During the 2013 RHIC run, the PHENIX experiment collected high statistics proton-proton collision data at $\sqrt{s} = 510$ GeV. Using the PHENIX muon spectrometers covering $1.2 < |\eta| < 2.4$, $J/\psi$ particles are identified by detecting the decayed $\mu^+ \mu^-$ pairs. The $J/\psi$ yield was studied against the charged particle multiplicity, measured by the recently installed forward silicon detectors. In this talk, the latest status of this analysis will be presented.

Speaker: Mr Haiwang Yu (PKU, NMSU, LANL)

Slides HaiwangYu.pdf

19:10 More discussions