Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session EB: Mini-Symposium on Mapping the QCD Phase Diagrams II |
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Chair: Mikhail Stephanov, University of Illinois at Chicago Room: Kona 4 |
Friday, October 16, 2009 9:00AM - 9:30AM |
EB.00001: Critical Properties of Quark Matter at Finite Temperature and Density Invited Speaker: We examine the nature the soft modes of the QCD phase transitions and their phenomenological consequences. In this talk, we mainly focus on the soft mode of the QCD critical point (CP) at finite $T$ and baryon chemical potential $\mu$. The QCD CP belongs to the same universality class $Z_2$ as that of the liquid-gas phase transition, and, hence a large density fluctuation is expected around the CP. We apply the relativistic fluid dynamics to analyse the dynamical properties of the density fluctuations, and show that its coupling with the thermal fluctuation is significant, which eventually overwhelms the density fluctuations. We show that the density mode is attenuated around the CP because of the divergence of the correlation length $\xi$. We speculate that if a suppression or disappearance of Mach cone is observed as the incident energy is lowered, say to 40 GeV/A at RHIC, it could be a signal of the existence of the QCD CP. We also mention the critical phenomena of the chiral transition and the color superconductivity at finite $T$. [Preview Abstract] |
Friday, October 16, 2009 9:30AM - 9:45AM |
EB.00002: Equation of State and Phase Instabilities near the Chiral Critical Point Joseph Kapusta, Laszlo Csernai The thermodynamics and critical exponents of high temperature and dense matter near the chiral critical point is studied. The parameterized equation of state matches on to that calculated with lattice QCD at zero chemical potential and to the known properties of nuclear matter at zero temperature. The extent to which finite size effects wash out the phase separation near the critical point is determined. The degree to which the critical point acts as an attractor in high energy heavy ion collisions is also investigated. [Preview Abstract] |
Friday, October 16, 2009 9:45AM - 10:00AM |
EB.00003: Lattice study of ratios between Israel-Stewart parameters Yasuhiro Kohno, Masayuki Asakawa, Masakiyo Kitazawa, Chiho Nonaka, Scott Pratt Navier-Stokes equations are known as hydrodynamic equations which take account of effects of dissipations, i.e. the viscosities and heat conductivity. There are, however, problems in the relativistic Navier-Stokes equations, i.e. the equations violate causality. Israel-Stewart equations, which evade the problems of Navier-Stokes equations by introducing new parameters, such as relaxation times, have recently been used in describing the space-time evolution of the quark-gluon plasma produced in high energy heavy ion collisions. The viscosities and relaxation times are related to each other by imposing entropy constraints on the system. According to Boltzmann-Einstein principle, the probability distribution of the fluctuation in energy-momentum tensor is related to the entropy of the system. Applying this principle to the entropy in Israel-Stewart theory, one can obtain the ratios of the viscosities to the relaxation times. We evaluate the ratios of the viscosities to the relaxation times in SU(3) lattice gauge theory. This analysis reduces the number of phenomenological parameters that appear in Israel-Stewart equations. [Preview Abstract] |
Friday, October 16, 2009 10:00AM - 10:15AM |
EB.00004: Measurement of Low-mass Vector Mesons in the PHENIX experiment at RHIC Yuji Tsuchimoto Extensive study of heavy-ion collisions at RHIC has established the creation of a strongly coupled Quark Gluon Plasma~(sQGP). Study of the Chiral Symmetry restoration and degree of freedom of quarks is important for understanding of the sQGP properties. The spectral shape of the Low-mass Vector Mesons~(LVM's), $\rho$, $\omega$ and $\phi$ can be modified in the medium by the partial restoration of Chiral symmetry. Due to the short life times of the LVMs, this modification can be directly studied by measuring low-momentum LVM via their decays into electron pairs, which do not participate in strong interaction and keep their properties unchanged throughout the evolution of the system. Since the width of the meson may be affected in the medium, the branching ratio of various decay modes may also be modified from vacuum values. In particular, the branching ratio of $\phi\rightarrow e^+e^-$ and $\phi\rightarrow K^+K^-$ may be sensitive to the modification due to the small Q-value of $\phi \rightarrow K^+K^-$. Suppression of $\phi$ at high-$p_{\rm T}$ in Au+Au collisions is interesting to discuss flavor dependence of quark energy loss in the QGP. The $R_{\rm AA}$ of $\phi$ suggests the suppression is guided by the number and flavor of valence quarks rather than by hadron mass. The PHENIX experiment has measured $\omega$ and $\phi$ production using di-electron and different hadronic decay channels at mid-rapidity at $\sqrt{s_{\rm NN}}$=200 GeV/c$^2$ p+p, d+Au and Au+Au collisions. [Preview Abstract] |
Friday, October 16, 2009 10:15AM - 10:30AM |
EB.00005: Dielectron mass spectra from $\sqrt{s_{\rm NN}}$ = 200 GeV heavy ion collisions at PHENIX Sarah Campbell The dielectron mass spectrum consists of light vector meson decays, in addition to decays from other hadronic and photonic sources. In heavy ion collisions, light vector mesons may be modified by the medium via chiral symmetry restoration and thermal radiation, providing additional signals at low masses above known hadronic sources. The PHENIX $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au analysis has measured a centrality dependent excess in the the low mass region (0.15 $GeV/c^{2} < m_{ee} < 0.75 GeV/c^{2}$) over the cocktail of known hadronic sources. The status of the PHENIX $\sqrt{s_{\rm NN}}$ = 200 GeV Cu+Cu analysis, in minimum bias and separated into centrality classes, will be shown, providing additional sensitivity in the study of this centrality dependent trend. [Preview Abstract] |
Friday, October 16, 2009 10:30AM - 10:45AM |
EB.00006: Masses of vector bosons in two-color dense QCD based on the hidden local symmetry Tetsuro Yamaoka, Masayasu Harada, Chiho Nonaka In two-color QCD the chiral SU(2N$_{f})$ symmetry is spontaneously broken to the Sp(2N$_{f})$ symmetry. The Nambu-Goldstone bosons (NG bosons) carrying the baryon charge also appear together with the mesonic NG bosons in the low energy effective theory. It is known that the condensation of baryonic NG bosons cause the spontaneous breaking of U(1)$_{B}$ symmetry at a certain finite baryon density. Based on the hidden local symmetry (HLS), we construct the chiral effective Lagrangian for two-color QCD with two-flavor quarks at finite baryon density. The effective Lagrangian includes the NG bosons and the vector bosons expressing the ordinary mesons with J$^{P}$ = 1$^{-}$ and the (anti-) baryons with J$^{P}$ = 1$^{+}$. We study the vacuum structure of this system and show the chemical potential dependence of the masses of (anti-) baryonic vector bosons. We show that the masses of (anti-) baryonic vector bosons change their behavior at the critical chemical potential for the U(1)$_{B}$ symmetry breaking. [Preview Abstract] |
Friday, October 16, 2009 10:45AM - 11:00AM |
EB.00007: Identified Charged Hadron Spectra at RHIC and Phase of QCD from PHENIX Tatsuya Chujo It is widely accepted that the new state of QCD matter, Quark Gluon Plasma (QGP), has been produced in central Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Among many experimental data, a baryon production provides an unique tool to investigate the phase of QCD, and to characterize the properties of QGP. It is interesting that how the experimental observables, such as a high $p_T$ hadron yield suppression and baryon enhancement, change as a function of system sizes and beam energies, and how they are affected by the existence of the QCD critical end point, which may be accessible by the lower beam energy scan proposed in the future RHIC program. In this talk, we will review the existing data of single particle spectra measured at RHIC in p+p (62.4, 200 GeV), Cu+Cu (22.5, 62.4, 200 GeV), Au+Au (62.4, 200 GeV). The most recent data of identified charged hadron spectra in p+p collisions at $\sqrt{s}$ = 62.4 and 200 GeV from PHENIX will be shown. Using these data, we investigate the evolutions of (1) $x_T$ scaling for baryons and mesons, (2) baryon enhancement determined by the nuclear modification factor ($R_{AA}$) and p/$\pi$ ratio, and (3) freeze-out properties. We will also discuss a potential connection between the phase of QCD and the evolutions of these experimental observables. [Preview Abstract] |
Friday, October 16, 2009 11:00AM - 11:15AM |
EB.00008: $K/\pi$ and $p/\pi$ Fluctuations in Au+Au Collisions in STAR Gary Westfall The freeze-out of an extended, strongly-interacting system created in a relativistic heavy ion collision near the QCD critical endpoint could create observable non-statistical fluctuations in net charge, strangeness and baryon number. We present results for $K/\pi$ and $p/\pi$ fluctuations from central Au+Au collisions at $\sqrt{s_{NN}}$ = 20, 62.4, 130, and 200 GeV in terms of the variable $\sigma_{\rm dyn}$. We compare these results with recent data from NA49 [1] for central Pb-Pb collisions. The energy dependence of the present data for central collisions extends smoothly from the NA49 measurements. We present the centrality dependence of $K/\pi$ and $p/\pi$ fluctuations from Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV in terms of the variable $\nu_{{\rm dyn},K\pi}$ . To minimize contributions from background protons, we restrict our measurements for $p$ and $\overline{p}$ to the transverse momentum range $0.4 < p_{t} < 1.0$ GeV/c. We present results for $K/\pi$ and $p/\pi$ fluctuations separated by sign as a function of centrality. In addition, we present results for net charge fluctuations ($\pi^+/\pi^-$), net strangeness fluctuations ($K^+/K^-$), and net baryon fluctuations ($p/\overline{p}$). We compare our results with the predictions of the Statistical Hadronization, HIJING, UrQMD, and HSD models.\\[4pt] [1] T. Anticic et al., Phys. Rev. C {\bf 79}, 044910 (2009). [Preview Abstract] |
Friday, October 16, 2009 11:15AM - 11:30AM |
EB.00009: $p/K$ Fluctuations from Au+Au Collisions at RHIC Jian Tian Event-by-Event fluctuations may be employed to probe the dynamics of dense matter hadronization and possibly be sensitive to critical behavior in the evolution of QCD matter [1]. In the framework of quark coalescence for particle production, baryon to meson ratios may be sensitive to local parton densities. The measurement of $p/K$ ratios also involves both baryon and strangeness quantum numbers in nuclear collisions. Fluctuations in the parton density and ratios will be used to search for possible critical point in nucleus-nucleus collisions. We will present measurements of fluctuations on $p/K$ multiplicity ratios from Au+Au collisions using the STAR detector. Fluctuations from Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV and 62.4 GeV with various collision centralities will be compared. Different analysis techniques and comparisons with the AMPT model calculation will be used to illustrate the effects of resonance decays and pair production on the particle ratios. [Preview Abstract] |
Friday, October 16, 2009 11:30AM - 11:45AM |
EB.00010: Baseline study for Chiral Symmetry Restoration using the Hadron Blind Detector in the PHENIX Experiment Sky Rolnick Measurement of the dielectron spectrum in p-p collisions at sqrt(s)=200GeV will be presented as a baseline study of Chiral Symmetry Restoration using the Hadron Blind Detector for the PHENIX experiment. Dielectrons offer us an ideal probe for studying ``medium'' modifications of vector mesons due to their color neutrality. Large combinatorial backgrounds, primarily from Dalitz decays and conversion pairs, limit the feasibility of such measurements. The Hadron Blind Detector has been specifically designed to rule out these backgrounds and offers a rejection factor of background of several orders of magnitude. In this study I will present various clustering algorithms and their behavior in high multiplicity environments such as central AuAu collisions as well as their expected rejection factors. This work should pave the road for very clean measurements of the dielectron continuum within the PHENIX experiment in the near future. [Preview Abstract] |
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