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Volume 10 Issue 6 - Critical point and onset of deconfinement

December 2012

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Contents
Journal Overview

Open Access December 4, 2012

Critical point and onset of deconfinement

Feng Liu, Yuanfang Wu, Nu Xu, Daicui Zhou

Page range: 1229-1229

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Open Access December 4, 2012

Measurements of heavy flavor and di-electron production at STAR

Gang Wang

Page range: 1230-1233

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Abstract

Heavy quarks are produced early in the relativistic heavy ion collisions, and provide an excellent probe into the hot and dense nuclear matter created at RHIC. In these proceedings, we will discuss recent STAR measurements of heavy flavor production, to investigate the heavy quark interaction with the medium. Electromagnetic probes, such as electrons, provide information on the various stages of the medium evolution without modification by final stage interactions. Di-electron production measurements by STAR will also be discussed.

Open Access December 4, 2012

Determination of freeze-out conditions from lattice QCD calculations

Frithjof Karsch

Page range: 1234-1237

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Abstract

Freeze-out conditions in Heavy Ion Collisions are generally determined by comparing experimental results for ratios of particle yields with theoretical predictions based on applications of the Hadron Resonance Gas model. We discuss here how this model dependent determination of freeze-out parameters may eventually be replaced by theoretical predictions based on equilibrium QCD thermodynamics.

Open Access December 4, 2012

Highlights of the beam energy scan from STAR

Alexander Schmah

Page range: 1238-1241

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Abstract

The first part of the beam energy scan (BES) program at RHIC was successfully completed in the years 2010 and 2011. First STAR results from particle yield measurements are in good agreement with previously published data from SPS and AGS experiments whereas other results like azimuthal HBT and K/π event-by-event fluctuations differ at some energies. In addition, new observations like the centrality dependence of chemical freeze-out parameters (T ch and µB) or the smoothly increasing difference with decreasing energy in the elliptic flow v 2 between particles and corresponding anti-particles, are discussed.

Open Access December 4, 2012

VISHNU hybrid model for the viscous QCD matter at RHIC and LHC energies

Huichao Song

Page range: 1242-1244

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Abstract

In this proceeding, we briefly describe the viscous hydrodynamics + hadron cascade hybrid model VISHNU for relativistic heavy ion collisions and report the current status on extracting the QGP viscosity from elliptic flow data.

Open Access December 4, 2012

Search for the critical point and the onset of deconfinement

Christoph Blume

Page range: 1245-1253

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Abstract

A review of the current experimental situation on the search for a critical point in the QCD phase diagram and the onset of deconfinement is given. Ongoing (STAR, NA61), as well as previous (NA49) experiments are presented. Their main results up-to-now are summarized and their findings are put into a general context. The future experimental program (CBM at FAIR, MPD at NICA) is discussed as well.

Open Access December 4, 2012

Probing the QCD chiral cross-over transition in heavy ion collisions

Krzysztof Redlich

Page range: 1254-1257

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Abstract

We argue that by measuring higher moments of the net proton number fluctuations in heavy ion collisions (HIC) one can probe the QCD chiral cross-over transition experimentally. We discuss the properties of fluctuations of the net baryon number in the vicinity of the chiral cross-over transition within the Polyakov loop extended quark-meson model at finite temperature and baryon density. The calculation includes non-perturbative dynamics implemented within the functional renormalization group approach. We find a clear signal for the chiral cross-over transition in the fluctuations of the net baryon number. We address our theoretical findings to experimental data of the STAR Collaboration on energy and centrality dependence of the net proton number fluctuations and their probability distributions in HIC.

Open Access December 4, 2012

Induced anomalous current in relativistic hydrodynamics with chiral anomaly

Shi Pu, Jian-hua Gao

Page range: 1258-1260

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Abstract

We discuss the triangle anomalous hydrodynamics in the presence of an external magnetic field B µ. Without loss of generality, we consider the case of a conserved vector current and non-conserved axial current. In order to ensure the positivity of the entropy production rate, two new terms proportional to the magnetic field B µ and the vorticity ω µ, which are associated with the Chiral Magnetic Effect and Chiral Vortical Effect in heavy ion collisions, need to be introduced. The transport coefficients of these new terms are also determined by the entropy principle.

Open Access December 4, 2012

Finite size scaling on the phase diagram of QCD

Sourendu Gupta

Page range: 1261-1266

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Abstract

In the last few years there has been remarkable progress in the comparison of experimental data on the shape of event-by-event distributions of conserved quantities and lattice thermodynamic predictions based on the grand canonical ensemble. In this talk we discuss how the QCD crossover temperature and the freezeout curve are extracted from the analysis of fluctuations. We report that one can also go further and locate the QCD critical point at µ }~ 2T c. We also list the systematics which must be brought under control in future.

Open Access December 4, 2012

The horn, kink and step, dale: from few GeV to few TeV

Anar Rustamov

Page range: 1267-1270

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Abstract

Rich experimental data have been collected in heavy-ion collisions at high energies to study the properties of strongly interacting matter. As the theory of strong interactions, QCD, predicts asymptotic freedom, the created matter at sufficiently high temperature and density will be dominated by a state of quasi-free quarks and gluons referred to as the Quark-Qluon Plasma (QGP). Experimental signals for the onset of the QGP creation (the onset of the deconfinement) have been predicted within the statistical model for the early stage of nucleus-nucleus collisions. In this model the existence of two different phases is assumed: confined mater and the QGP, as well as a first order phase transition between them. Until recently, these predictions were confirmed only by the NA49 experiment at the CERN SPS. In this report recent results from STAR at RHIC/BNL and from ALICE at LHC/CERN, related to the onset of deconfinement, will be compared to published results from NA49.

Open Access December 4, 2012

Directed flow from global symmetry and initial state Fluctuations

Laszlo Csernai, Astrid Skålvik, D. Wang, Daniel Strottman, Csaba Anderlik, Yun Cheng, Yu Yan, Ben Sa

Page range: 1271-1273

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Abstract

Collective flow is studied in a 3+1D fluid dynamical model with globally symmetric, peripheral initial conditions, taking into account the shear flow. At $\sqrt {s_{NN} } $ = 2.76 TeV in semi-peripheral Pb+Pb collisions this leads to rotation, while at more peripheral collisions with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholz instability is observed. This effect provides a precision tool for studying the viscosity of Quark-Gluon Plasma.

Open Access December 4, 2012

Centrality dependence of freeze-out parameters from Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7, 11.5 and 39 GeV

Lokesh Kumar

Page range: 1274-1277

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Abstract

The RHIC beam energy scan program in its first phase collected data for Au+Au collisions at beam energies of 7.7, 11.5 and 39 GeV. The event statistics collected at these lower energies allow us to study the centrality dependence of various observables in detail, and compare to fixed-target experiments at SPS for similar beam energies. The chemical and kinetic freeze-out parameters can be extracted from the experimentally measured yields of identified hadrons within the framework of thermodynamical models. These then provide information about the system at the stages of the expansion where inelastic and elastic collisions of the constituents cease. We present the centrality dependence of freeze-out parameters for Au+Au collisions at midrapidity for $\sqrt {s_{NN} } $ = 7.7, 11.5, and 39 GeV from the STAR experiment. The chemical freeze-out conditions are obtained by comparing the measured particle ratios (involving π, K, p, and p) to those from the statistical thermal model calculations. The kinetic freeze-out conditions are extracted at these energies by simultaneously fitting the invariant yields of identified hadrons (π, K, and p) using Blast Wave model calculations.

Open Access December 4, 2012

Probing the QCD critical point with relativistic heavy-ion collisions

Steffen Bass, Hannah Petersen, Cory Quammen, Hal Canary, Christopher Healey, Russell Taylor

Page range: 1278-1281

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Abstract

We utilize an event-by-event relativistic hydrodynamic calculation performed at a number of different incident beam energies to investigate the creation of hot and dense QCD matter near the critical point. Using state-of-the-art analysis and visualization tools we demonstrate that each collision event probes QCD matter characterized by a wide range of temperatures and baryo-chemical potentials, making a dynamical response of the system to the vicinity of the critical point very difficult to isolate above the background.

Open Access December 4, 2012

Scaling properties and charge dependence of particle ratio fluctuations at RHIC

Hui Wang

Page range: 1282-1284

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Abstract

It has been suggested that the existence of a QCD phase transition would cause an increase and divergence of fluctuations. Thus event-by-event particle ratio fluctuations could be used to study strangeness and baryon number fluctuations near the critical point in the QCD phase diagram. In this paper, we present dynamical K/π, p/π, and K/p ratio fluctuations from Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7 to 200 GeV. Charge dependent results as well as multiplicity scaling properties of these fluctuation results are discussed. The STAR data are compared to different theoretical model predictions and previous experimental results.

Open Access December 4, 2012

New results from fluctuation analysis in NA49 at the CERN SPS

Maja Maćkowiak-Pawłowska

Page range: 1285-1288

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Abstract

The exploration of the phase diagram of strongly interacting matter, particularly the study of the phase transition from hadronic to partonic matter and the search for a hypothetical critical endpoint of the first order transition line, is one of the most challenging tasks in present heavy ion physics. New results on chemical (particle ratio), transverse momentum, multiplicity and azimuthal angle fluctuations are presented. We also discuss their connection to the onset of deconfinement and to the critical endpoint.

Open Access December 4, 2012

The compressed baryonic matter experiment at FAIR

Peter Senger

Page range: 1289-1294

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Abstract

The Compressed Baryonic Matter (CBM) experiment will be one of the major scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of the CBM research program is to explore the QCD phase diagram in the region of high baryon densities using high-energy nucleus-nucleus collisions. This includes the study of the equation-of-state of nuclear matter at high densities, and the search for the deconfinement and chiral phase transitions. The CBM detector is designed to measure both bulk observables with large acceptance and rare diagnostic probes such as charmed particles and vector mesons decaying into lepton pairs.

Open Access December 4, 2012

Investigating the microscopic properties of strongly interacting matter with HADES

Tetyana Galatyuk, Manuel Lorenz

Page range: 1295-1301

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Abstract

In the energy domain of 1–2 GeV kinetic energy per nucleon, HADES has measured rare and penetrating probes in elementary and heavy ion collisions. Our results demonstrate that electron pair emission in C+C collisions can essentially be explained as a superposition of independent N+N collisions. HADES results on e+e− production in Ar+KCl collisions, however, show a strong enhancement of the dilepton yield relative to a reference spectrum obtained from elementary nucleon-nucleon reactions, signal the onset of medium effects beyond the superposition of individual N+N collisions. Intriguing results where also obtained from the reconstruction of hadrons with open and hidden strangeness. Analyses of the experimentally obtained hadronic yields measured in Ar+KCl allows to extract the chemical freeze-out conditions in the T -µB phase diagram of strongly interacting matter. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double strange baryon ≡− appears about ten times more abundant than expected. This result will be discussed in the context of the exploration of the nuclear matter phase diagram in the region of finite density. Further investigations to search for significant medium effects, will be followed over the coming years with an upgraded HADES detector.

Open Access December 4, 2012

Resonance states in an effective chiral hadronic model

Philip Rau, Jan Steinheimer, Stefan Schramm, Horst Stöcker

Page range: 1302-1305

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Abstract

With an effective chiral flavour SU(3) model we show the effect of hadronic resonances on the QCD phase diagram. We state that varying the resonance couplings to the scalar and vector fields affects the order and location of the phase transition, the possible existence of a critical end point (CEP), and the thermodynamic properties. We present (strange) quark number susceptibilities at zero baryochemical potential and at three different points at the phase transition. Comparing results to lattice QCD, we state that reasonable large vector couplings limit the phase transition to a smooth crossover ruling out a CEP.

Open Access December 4, 2012

Collective flow and correlation with higher harmonic event planes

ShinIchi Esumi

Page range: 1306-1310

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Abstract

Azimuthal event anisotropy and particle correlation have been used to analyze the collectivity of the system created in the high-energy heavy-ion collisions in order to study the properties of Quark Gluon Plasma (QGP). Higher harmonic event anisotropy is recently recognized to carry the information of initial participant geometrical fluctuation because of the finite number of participating nucleons in heavy-ion collisions. The system response after the collective expansion can be observed as higher harmonic event anisotropy, the n-th harmonic order dependence can be used to further constrain the hydro-dynamical properties of the system. The multi-particle azimuthal correlation with respect to the higher harmonic event plane can be used as a tool to understand the origin of the higher harmonic event anisotropy and its relation to the medium response from the jet-quenching as soft-hard interplay. Recent results on the higher harmonic event anisotropy measurements and an attempt of two-particle correlation analysis with respect to the higher harmonic event planes are discussed.

Open Access December 4, 2012

Understanding of radial and elliptic expansion with quark number scaling and blast wave model in 200 GeV Au+Au at RHIC-PHENIX

Yoshimasa Ikeda

Page range: 1311-1313

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Abstract

Measurement of azimuthal anisotropy is one of the most important study because of its relation to the initial stage. Especially, the elliptical anisotropy which is measured as the second coefficient of Fourier expansion of particle azimuthal distribution is believed to carry the information about the initial geometrical anisotropy. It seems the identified hadron v 2 depends on the number of quark contents of the hadron. The experimental result of quark number scaling of v 2 suggests quark level collectivity in the hot dense matter and quark coalescence mechanism to form hadron from quark matter via quark-gluon phase transition. The measured v 2 and p T spectra are analyzed with various assumptions based on the blast wave model in order to understand the freeze-out temperature and collective flow after the system expansion.

Open Access December 4, 2012

Baryon number cumulants and proton number cumulants in relativistic heavy ion collisions

Masayuki Asakawa

Page range: 1314-1317

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Abstract

Baryon number cumulants are invaluable tools to diagnose the primordial stage of heavy ion collisions. In experiments, however, proton number cumulants have been measured as substitutes. In fact, proton number fluctuations are further modified in the hadron phase and different from those of baryon number. We give formulas that express the baryon number cumulants solely in terms of proton number fluctuations, which are experimentally observable.

Open Access December 4, 2012

What favors and disfavors the critical point of QCD?

Kenji Fukushima

Page range: 1318-1321

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Abstract

Results from chiral effective models suggest the existence of the so-called QCD critical point. These model predictions are highly dependent on the model setup and there is no universal argument for its existence and location. I discuss why a first-order phase transition is generally favored in models at low temperature T and high chemical potential µ, which will explain why the model results are unreliable about the critical point. I propose a useful way to reinterpret the model results as a liquid-gas-type phase transition like that of nuclear matter. This picture provides us with a fairly model-independent description of the QCD critical point not relying on detailed phase structures.

Open Access December 4, 2012

Numerical study of QCD phase diagram at high temperature and density by a histogram method

Shinji Ejiri, Sinya Aoki, Tetsuo Hatsuda, Kazuyuki Kanaya, Yoshiyuki Nakagawa, Hiroshi Ohno, Hana Saito, Takashi Umeda

Page range: 1322-1325

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Abstract

We study the QCD phase structure at high temperature and density adopting a histogram method. Because the quark determinant is complex at finite density, the Monte-Carlo method cannot be applied directly. We use a reweighting method and try to solve the problems which arise in the reweighting method, i.e. the sign problem and the overlap problem. We discuss the chemical potential dependence of the probability distribution function in the heavy quark mass region and examine the applicability of the approach in the light quark region.

Open Access December 4, 2012

Higher-order ratios of baryon number cumulants

Bernd-Jochen Schaefer, Mathias Wagner

Page range: 1326-1329

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Abstract

The relevance of higher order cumulants of net baryon number fluctuations for the analysis of freeze-out and critical conditions in heavy-ion collisions at LHC and RHIC is addressed. The sign structure of the higher order cumulants in the vicinity of the chiral crossover temperature might be a sensitive probe and may allow to elucidate their relation to the QCD phase transition. We calculate ratios of generalized quarknumber susceptibilities to high orders in three flavor QCD-like models and investigate their sign structure close to the chiral crossover line.

Open Access December 4, 2012

Search for critical fluctuations of the proton density in central A+A collisions at maximum SPS energy

Nikolaos Antoniou, Nikos Davis, Fotis Diakonos

Page range: 1330-1332

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Abstract

We performed an intermittency analysis of the proton density fluctuations in transverse momentum space for the collisions Si+A (A=Al,Si,P) and C+A (A=C,N) at maximum SPS energy $\sqrt {s_{NN} } $ ≈ 17 GeV). In our analysis we used exclusively proton tracks in the midrapidity region (|y CM| ≤ 0.75). For the Si+A system we find signature of power-law distributed density fluctuations quantified by the intermittency index ϕ 2 which approaches in size the predictions of critical QCD [Phys. Rev. Lett. 97, 032002 (2006)]. This result supports further the recent findings of power-law fluctuations in the density of (π +, π −) pairs with invariant mass close to their production threshold for the Si+Si at the same energy, reported in [Phys. Rev. C 81, 064907 (2010)].

Open Access December 4, 2012

Status and plans of the ion program of NA61 at the CERN SPS

Katarzyna Grebieszkow

Page range: 1333-1337

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Abstract

The NA61/SHINE at the CERN SPS is a new experiment to study hadron production in p+p, p+A, h+A and A+A interactions. The main goal of the NA61 ion program is to explore the phase diagram (T − µB) of strongly interacting matter. In particular, we plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. A two-dimensional scan of the phase diagram will be performed by varying the energy (13A–158A GeV) and system size (p+p, Be+Be, Ar+Ca, Xe+La) of collisions. This paper summarizes the status and plans of the NA61/SHINE ion program. In particular the detector upgrades, data taking schedule and the first results on spectra and correlations are discussed.

Open Access December 4, 2012

Probing the QCD phase boundary with elliptic flow in relativistic heavy ion collisions at STAR

Shusu Shi

Page range: 1338-1340

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Abstract

We present measurement of elliptic flow, v 2, for charged and identified particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7–39 GeV. We compare the inclusive charged hadron v 2 to those from transport model calculations, such as the UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in v 2 between particles and anti-particles. The v 2 of ϕ meson is observed to be systematically lower than other particles in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 GeV.

Open Access December 4, 2012

Finite-size behaviour of a critical related observable

Wu Yuanfang, Chen Lizhu, Pan Xue, Shao Ming, Xiaosong Chen

Page range: 1341-1344

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Abstract

Accounting for the influence of system size in relativistic heavy ion collisions, the finite-size form of a critical related observable is suggested. The fixed-point and straight line methods are proposed in exploring the QCD critical point and phase boundary in relativistic heavy ion collisions. As an application, the finitesize behaviour of the ratios of higher net-proton cumulants, dynamical electric charge fluctuations, and transverse momentum correlations in Au + Au collisions at RHIC are examined.

Open Access December 4, 2012

KS0, Λ and ≡ production at intermediate to high pT from Au+Au collisions at $\sqrt {s_{NN} } $ = 39, 11.5 and 7.7 GeV

Xianglei Zhu

Page range: 1345-1348

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Abstract

We report on the p T dependence of nuclear modification factors (R CP) for KS0, Λ, ≡ and the $\bar NK_S^0 $ ratios at mid-rapidity from Au+Au collisions at $\sqrt {s_{NN} } $ = 39, 11.5 and 7.7 GeV. At $\sqrt {s_{NN} } $ = 39 GeV, the R CP data show a baryon/meson separation at intermediate p T and a suppression for KS0 for p T up to 4.5 GeV/c; the $\bar \Lambda K_S^0 $ shows baryon enhancement in the most central collisions. However, at $\sqrt {s_{NN} } $ = 11.5 and 7.7 GeV, R CP shows less baryon/meson separation and $\bar NK_S^0 $ shows almost no baryon enhancement. These observations indicate that the matter created in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 or 7.7 GeV might be distinct from that created at $\sqrt {s_{NN} } $ = 39 GeV.

Open Access December 4, 2012

Comparison of viscosities from the Chapman-Enskog and relaxation time methods

Anton Wiranata, Madappa Prakash, Purnendu Chakraborty

Page range: 1349-1351

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Abstract

A quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods is performed for selected test cases with specified elastic differential cross sections: (i) the non-relativistic, relativistic and ultra-relativistic hard sphere gas with angle and energy independent differntial cross section, (ii) the Maxwell gas, (iii) chiral pions and (iv) massive pions. Our quantitative results reveal that the extent of agreement (or disagreement) depends very sensitively on the energy dependence of the differential cross sections employed.

Open Access December 4, 2012

Di-lepton production in heavy-ion collisions and the QCD phase diagram

Yifei Zhang, Haojie Xu, Wangmei Zha, Qun Wang

Page range: 1352-1356

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Abstract

We reproduce di-electron spectra in the region of 0 < m e+e < 4 GeV in both minimum bias and central Au+Au collisions at $\sqrt {s_{NN} } $ = 200 GeV measured by the STAR experiment. A cocktail simulation, incorporating STAR acceptance and detector responses, is able to describe the “enhancement” of the low mass region by including an in-medium modification of vector mesons and a thermal di-lepton calculation. We also predict the di-lepton mass spectra in RHIC lower energies via an extrapolation method. The evolution of Di-lepton mass spectra, effective temperature, and possible medium modifications versus colliding energies are studied to explore the QCD phase diagram.

Open Access December 4, 2012

The chiral and deconfinement phase transitions

Fukun Xu, Mei Huang

Page range: 1357-1360

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Abstract

By introducing the dressed Polayakov loop or dual chiral condensate as a candidate order parameter to describe the deconfinement phase transition for light flavors, we discuss the interplay between the chiral and deconfinement phase transitions, and propose the possible QCD phase diagram at finite temperature and density. We also introduce a dynamical gluodynamic model with dimension-2 gluon condensate, which can describe the color electric deconfinement as well as the color magnetic confinement.

Open Access December 4, 2012

Multi-strange baryon elliptic flow in Pb-Pb collisions at $\sqrt {s_{NN} } $ = 2.76 TeV measured with the ALICE detector

Zhongbao Yin

Page range: 1361-1364

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Abstract

We present the results on elliptic flow with multi-strange baryons produced in Pb-Pb collisions at $\sqrt {s_{NN} } $ = 2.76 TeV. The analysis is performed with the ALICE detector at LHC. Multi-strange baryons are reconstructed via their decay topologies and the v 2 measurements are analyzed with the two-particle scalar product method. The p T differential v 2 values are compared to the viscous hydrodynamical (VISH2+1) model calculation and to the STAR measurements in Au-Au collisions at $\sqrt {s_{NN} } $ = 200 GeV. We found that the model describes ≡ and Ωv 2 measurements within uncertainties. The differential v 2 of ≡ and Ω is similar to the STAR measurements at 200 GeV in Au-Au collisions.

Open Access December 4, 2012

Event-by-event hadron ratio fluctuations from Au+Au collisions at RHIC-STAR

Jian Tian

Page range: 1365-1368

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Abstract

We present measurements of event-by-event fluctuations on hadron multiplicity ratios (K/π, p/π, K/p) in Au+Au collisions at $\sqrt {s_{NN} } $ and 200 GeV using the STAR detector at RHIC. The magnitude of dynamical fluctuations σ dyn for p/π and K/p ratios change smoothly from a large negative value at 7.7 GeV to a smaller negative value at 200 GeV while that for the K/π ratios exhibits no significant beam energy dependence. The dynamical fluctuations related to pair production σ dynpair dyn for the p/K, K/p, K −/K + and p/p ratios at 200 GeV all exhibit a maximum at the mid-central collisions and decrease at the most peripheral and most central collisions.

Open Access December 4, 2012

Refractive index of light and the quark-gluon plasma

Juan Liu, Min-Jie Luo, Hao-Jie Xu

Page range: 1369-1371

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Abstract

The refractive index (RI) of light propagating in a medium of quark-gluon plasma (QGP) is studied. The weakly coupled QGP is studied in the framework of hard-thermal-loop (HTL) perturbation theory, and the strongly coupled one is treated based on the holographic approach. In more realistic setups, the feasibility of observing the optical phenomenon related to the RI of QGP is also discussed.

Open Access December 4, 2012

Probing the QCD critical point by higher moments of net-proton multiplicity distributions at STAR

Xiaofeng Luo

Page range: 1372-1374

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Abstract

Higher moments (kurtosis (κ), skewness (S) and variance (σ 2)) of multiplicity distributions are sensitive to the correlation length and can be used to search for the QCD critical point. The moment products κσ 2 and S σ of net-proton distributions, which are also related to volume independent baryon number susceptibility ratios, can be compared with Lattice QCD and Hadron Resonance Gas (HRG) model calculations. We discuss the recent progress in the higher moments analysis of net-protons multiplicity distributions.

Open Access December 4, 2012

Baryon and electric charge fluctuations at crossover

Vladimir Skokov

Page range: 1375-1378

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Abstract

We discuss the higher order cumulants of net-baryon and electric charge fluctuations as a probe of the QCD crossover. The sensitivity of the higher order cumulants in the hadron resonance gas model to an inclusion of repulsive interactions is also considered.

Open Access December 4, 2012

Hard-thermal-loop QCD trace anomaly

Nan Su

Page range: 1379-1381

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Abstract

In this proceedings I summarize results of QCD trace anomaly from recent three-loop hard-thermal-loop perturbation theory (HTLpt) calculations. I focus on the trace anomaly scaled by T 2 for pure-glue and N f = 3 QCD. The comparison to available lattice data suggests that for pure-glue QCD agreement between HTLpt results and lattice data for the trace anomaly begins at temperatures above 8 T c while when including quarks (N f = 3) agreement begins already at temperatures above 2 T c. The results in both cases indicate that at very high temperatures the T 2-scaled trace anomaly increases with temperature in accordance with the predictions of HTLpt.

Open Access December 4, 2012

Center-symmetric effective theory for two-color quark matter

Tomáš Brauner

Page range: 1382-1384

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Abstract

We revisit the center-symmetric dimensionally reduced effective theory for two-color Yang-Mills theory at high temperature. This effective theory includes an order parameter for deconfinement and thus allows to broaden the range of validity of the conventional three-dimensional effective theory (EQCD) towards the confining phase transition. We extend the previous results by including the effects of massive quarks with nonzero baryon chemical potential. The parameter space of the theory is constrained by leading-order matching to the Polyakov loop effective potential of two-color QCD. Once all the parameters are fixed, the effective theory can provide model-independent predictions for the physics above the deconfinement transition, thus bridging the gap between large-scale numerical simulations and semi-analytical calculations within phenomenological models.

Open Access December 4, 2012

Equation of state at non-zero baryon density based on lattice QCD

Pasi Huovinen, Péter Petreczky, Christian Schmidt

Page range: 1385-1387

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Abstract

We employ the lattice QCD data on Taylor expansion coefficients to extend our previous parametrization of the equation of state to finite baryon density. When we take into account lattice spacing and quark mass dependence of the hadron masses, the Taylor coefficients at low temperature are equal to those of hadron resonance gas. Parametrized lattice equation of state can thus be smoothly connected to the hadron resonance gas equation of state at low temperatures.

Open Access December 4, 2012

PACIAE model capability in describing net proton moments

Ayut Limphirat, Dai-Mei Zhou, Yu-Liang Yan, Bao-Guo Dong, Chinorat Kobdaj, Yupeng Yan, Laszlo Csernai, Ben-Hao Sa

Page range: 1388-1391

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Abstract

PACIAE 2.0, a parton and hadron cascade model, is employed to investigate the dependence of the moments of net proton event distributions on reaction energies varying from RHIC to LHC energy in p + p collisions. It is found that net proton moments and moment products are sensitive to the collision energy except the moment product kσ 2 which is almost independent of the collision energy. The PACIAE results are in line with experimental data.

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Open Physics (PHYS) is a peer-reviewed, open access, electronic journal devoted to the publication of fundamental research results in all fields of physics. The journal provides the readers with free, instant, and permanent access to all content worldwide; and the authors with extensive promotion of published articles, long-time preservation, no space constraints and immediate publication.

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