### Session DA: Ultrarelativistic Heavy Ions I

Chair: Fuqian Wang, Purdue University
Room: 62

 Thursday, October 27, 2011 10:30AM - 10:42AM DA.00001: Chiral and deconfinement transition in QCD Peter Petreczky I present results on the chiral and deconfinement aspects of the QCD transition at finite temperature. Calculations have been performed using the highly improved staggered quark (HISQ) action with lattices of temporal extent $N_{\tau}=6$, $8$ and $12$, which allow one to control the approach to the continuum limit. While this action is superior to all previous improved staggered quark actions, it has been demostrated that in the continuum limit the previously used asqtad action gives consistent results. For the chiral transition temperature we find $T_c=157 \pm 6$ MeV. Thursday, October 27, 2011 10:42AM - 10:54AM DA.00002: Hadron Production and Freeze-Out Dynamics in $\sqrt{s_{NN}}$ Au+Au at RHIC Samantha Brovko The Beam Energy Scan (BES) program at RHIC was commissioned to search for the critical point and the turn-on of QGP signatures. STAR has collected data from collisions of $Au+Au$ at energies from 7.7 to 62.4 GeV per nucleon pair. The addition of a full-coverage Time-of-Flight detector at STAR has extended the momentum range for clean particle identification. The freeze-out parameters can be extracted from the measured hadron spectra. In this talk, we will present STAR preliminary results of particle spectra from $\sqrt{s_{NN}}$ = 19.6 GeV $Au+Au$ collisions. Distributions of $\pi, K, p$ and $\bar{p}$ as a function of $m_{T}-m_{0}$ will be used to discuss the chemical and kinetic freeze-out properties. In addition, we will compare these results with earlier BES data from STAR. Thursday, October 27, 2011 10:54AM - 11:06AM DA.00003: The shapes of the multiplicity distributions in $\sqrt{s_{\rm NN}}$$=7.7-200 GeV Au+Au Collisions at STAR Daniel McDonald A possible signature of the existence of a critical point in the phase diagram of nuclear matter is the non-monotonic behavior of the shape of the multiplicity distributions of particles reflecting the conserved quantities of baryon number, charge, or strangeness. These shapes are characterized with respect to Gaussian distributions via the variance and higher statistical moments, which may reflect the critical fluctuations that may diverge at beam energies near the critical point. The STAR experiment has measured Au+Au collisions at a wide range of beam energies, \sqrt{s_{\rm NN}}$$=$7.7$-$200 GeV, and is well suited for numerous measurements because of its wide, uniform acceptance and the extended particle identification from a newly-installed Time-of-Flight (TOF) system. The measurements of the shapes of the multiplicity distributions of net protons, net kaons, and net charge - via the statistical moments skewness, kurtosis, and the intensive normalized cumulants of Ref. [1] - will be described. \\[4pt] [1] C. Athanasiou {\it et al.}, Phys. Rev. D 82, 074008 (2010). Thursday, October 27, 2011 11:06AM - 11:18AM DA.00004: Strange Baryons Production in RHIC Beam Energy Scan Feng Zhao Strange baryon production is sensitive to the dynamics of deconfined quark-gluon matter created in heavy ion collisions. We have been investigating the strangeness enhancement and strangeness equilibration as a function of beam energy at RHIC. We have analyzed strange baryon production from Au+Au collision data at 7.7~GeV, 11.5~GeV and 39~GeV that STAR has collected during the RHIC beam energy scan in 2010. In this presentation, the $p_{T}$ spectra of $\Lambda$, $\Xi^{-}$, $\Omega^{-}$ and their antiparticles will be reported. The strangeness enhancement and nuclear modification factor of strange baryons at these energies will also be discussed. Thursday, October 27, 2011 11:18AM - 11:30AM DA.00005: Dynamical $K/\pi$, $p/\pi$, and $K/p$ Fluctuations in $\sqrt{s_{NN}}$ = 7.7-200 GeV Au+Au Collisions Terence Tarnowsky Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results from new measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations are presented. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 62.4, and 200 GeV. New results are compared to previous measurements and to theoretical predictions from several models. The measured dynamical $K/\pi$ fluctuations are found be independent of collision energy, while dynamical $p/\pi$ and $K/p$ fluctuations have a negative value that increases toward zero at top RHIC energy. Thursday, October 27, 2011 11:30AM - 11:42AM DA.00006: Energy dependence of the freeze out eccentricity from azimuthally-dependent HBT analyses at STAR Christopher Anson Non-central heavy ion collisions at RHIC create an anisotropic participant zone of QCD matter under extreme conditions of energy and matter density. While this zone is initially out-of- plane-extended, pressure gradients cause the hot, dense medium to expand preferentially in plane. Over time, this expansion makes the shape more spherical, perhaps even becoming extended in the in-plane direction. The change in shape is determined by the expansion and freeze-out time scales which depend, in part, on the early pressure gradients. As a result, the freeze-out shape may provide a sensitive probe of the Equation of State of hot QCD matter. The recent RHIC Beam Energy Scan, which covered energies from $\sqrt{s_{NN}}$ of 7.7 to 39 GeV provides an opportunity to explore the energy dependence of the freeze out eccentricity. The new low energy data from STAR complements high statistics data sets at $\sqrt{s_{NN}}$ of 62.4 and 200 GeV. The dependence of the HBT radius parameters on azimuthal angle relative to the reaction plane have been extracted. These dependences can be related to the freeze out eccentricity within the context of a blast wave model. We will present STAR's most recent results from azimuthally-dependent HBT analyses across a wide range of energies. Thursday, October 27, 2011 11:42AM - 11:54AM DA.00007: Pion-kaon femtoscopy in 200 GeV collisions in STAR at RHIC Yan Yang Correlations between non-identical particles at low relative momentum in the center of mass encode unique information on the space-time structure of the emitting system [1,2], in particular a space-time offset of one particle species (e.g. kaons) with respect to another (e.g. pions). We present new high-statistics measurements of pion-kaon correlations in 200 GeV in the spherical harmonic representation [3,4]. The analysis benefits greatly from the extended particle-identification capabilities of the recently installed STAR Time of Flight detector. In $\sqrt{s_{NN}}=200$ GeV $Au+Au$ collisions, we observe an asymmetry similar to that reported at lower energies with poorer statistics. Finally, we present a first similar analysis of $\sqrt{s}=200$ GeV $p+p$ collisions.\\[4pt] [1] Lisa, Pratt, Soltz and Wiedemann, Ann. Rev. Nucl. Part. Sci. {\bf 55}, 357 (2005) \newline [2] R. Lednicky, nucl-th/0112011 \newline [3] Z. Chajecki and M. Lisa, Phys. Rev. C {\bf 78}, 064903 (2008) \newline [4] A. Kisiel and D. Brown, Phys. Rev. C {\bf 80}, 064911 (2009) Thursday, October 27, 2011 11:54AM - 12:06PM DA.00008: Transverse Energy at RHIC in the Forward/Backward Direction using the PHENIX MPC Brett Fadem Transverse energy has been used to estimate energy density in ultra-relativistic heavy ion collisions and to discriminate between competing models of hadronic interactions. Furthermore, fluctuations in transverse energy might signal the presence of a critical point in the phase diagram of nuclear matter. The PHENIX Muon Piston Calorimeter (MPC) has acceptance in the range $3.1<|\eta|<3.8$. Status of the measurement of transverse energy using the PHENIX MPC at RHIC will be reported. Thursday, October 27, 2011 12:06PM - 12:18PM DA.00009: Forward Di-Hadron Correlations and RdA in d+Au Collisions at RHIC IhnJea Choi Measurements using the PHENIX forward detectors in high energy deuteron-gold collisions make it possible to study cold nuclear matter effects in nucleon structure. The high parton densities in nuclei at low-x lead to gluon fusion causing saturation of the gluon distribution and thus suppression of hadron production cross section. This saturation has been described as the formation of the Color Glass Condensate (CGC). A conclusive measurement discriminating between different mechanisms has yet to be carried out. CGC calculations predict significant suppression of conditional yields for rapidity separated hadron pairs with one of the hadrons at forward rapidity. Two new forward electromagnetic calorimeters (Muon Piston Calorimeters, $-3.1 < \eta < -3.7, 3.1 < \eta < 3.9$ ) allow the PHENIX experiment to further study forward di-hadron correlations and RdA which have been predicted to show dramatic effects due to gluon saturation. Azimuthal correlations of di- hadron pairs at different pseudorapidities and RdA of $\pi^{0}$ and $\eta$ will be shown. The forward pseudorapidity correlations are especially interesting because it is expected that they provide a test of gluon saturation down to $x$~10$^{-3}$ in the Au nucleus. The analysis presented is based on the high integrated luminosity data sample of d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV taken at RHIC in 2008. Thursday, October 27, 2011 12:18PM - 12:30PM DA.00010: Recent Performance of the Resistive Plate Chambers in the PHENIX Forward Trigger Upgrade Michael Daugherity The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is the world's only polarized proton-proton collider. The recent $\sqrt{s}=500$ GeV collisions enable a new W-boson physics program. Since W production is very sensitive to the spin-dependent quark distributions, these measurements will provide new insight into the spin structure of the proton. The PHENIX detector has undergone an extensive upgrade to significantly improve triggering on high-momentum muons produced by W decay at forward rapidity. The upgrade consists of new front-end electronics for the existing muon tracking chambers as well as new resistive plate chambers (RPCs) at two stations in each muon arm. This talk will review the current status and performance of the RPCs in the forward trigger upgrade from recently completed RHIC run 11.