Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session L13: Ultrarelativistic Heavy Ions: Hot and Dense Matter |
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Sponsoring Units: DNP Chair: Paul Sorensen, Brookhaven National Laboratory Room: Plaza Court 2 |
Sunday, April 14, 2013 3:30PM - 3:42PM |
L13.00001: Identified charged hadron spectra and ratios in Au+Au and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV Ron Belmont Identified hadrons are an important probe of the hot and dense nuclear medium created at RHIC. At low $p_T$ the particle yields are dominated by soft production and exhibit collective flow properties. At high $p_T$ the particle production is dominated by fragmentation and the yields exhibit suppression relative to the yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions. In the intermediate $p_T$ region, 2--6~GeV/c, there is an interplay between these effects and, in addition, different models of hadronization, such as parton recombination, may be needed to explain the data. While mesons, like pions and kaons, exhibit a suppression pattern of their yields in the intermediate $p_T$ region, baryons, like (anti)protons, exhibit almost no suppression. Furthermore, similar meson vs. baryon dynamics in the intermediate $p_T$ region are found in d+Au collisions, where no hot nuclear medium effects are present. While mesons exhibit a small Cronin enhancement, baryons exhibit a much stronger Cronin enhancement. In this talk, the transverse momentum ($p_T$) spectra and ratios of identified charged hadrons $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced in Au+Au and d+Au collisions at 200 GeV in different centrality bins will be presented. [Preview Abstract] |
Sunday, April 14, 2013 3:42PM - 3:54PM |
L13.00002: Bc absorption cross sections by light mesons in heavy ion collision M.A.K. Lodhi, Faisal Akram In relativistic heavy ion collision the production of strangeness would saturate, as a sign of quark-gluon plasma, leading to the fireball of matter expanding and finally breaking apart. That in turn would provide very high abundance of strange hadrons along with other particles. The interaction of those hadrons would be useful in calculating their production rate. The cross sections of Bc absorptions by pion- rho- and K- mesons have been calculated using hadronic Lagrangians based on SU(5) symmetry. The comparison of those cross sections shows some interesting anomalies, which will be discussed. [Preview Abstract] |
Sunday, April 14, 2013 3:54PM - 4:06PM |
L13.00003: SHARE with CHARM Michal Petran, Johann Rafelski The statistical hadronization model predicts particle production in hadronization of quark-gluon plasma~[1]. In LHC-ion 2.76 TeV per nucleon collision, a rather large yield of charm is expected, produced in initial hard parton collisions before the QGP phase emerges. Using statistical hadronization method, we predict the expected charmed hadron yields~[2]. Our effort is to include charm hadron decay contributions in final hadron yields. Based on experimental decay data, symmetry principles and plausibility arguments, we prepare a complete decay table of all charmed hadrons. CHARM module adds charm decay hadron multiplicity into SHARE~[1]. SHARE with CHARM utility uses the charm yield as an additional fit parameter when analyzing hadron production in HI-collisions, which works even without charmed hadron input. Based on precise non-charm hadron yields data, a prediction of charmed hadron production is obtained. About 20\% of charm is bound to strangeness and thus charm decays contribute a significant fraction of multistrange hadron yields: a 30\% fraction of $\phi$, 25\% of $\Xi$ and 30\% of $\Omega$ is produced by charm decays whereas e.g. $\pi$ yield increases by 10\%, (taking as a scaling benchmark 100 charm pairs and a common set of chemical non-equilibrium SHM parameters).\\[4pt] [1] G. Torrieri, et al., Comp.Phys.Comm. {\bf 167},229(2005); ibid.{\bf 175}, 635(2006)\\[0pt] [2] I. Kuznetsova and J. Rafelski, Eur.Phys.J. {\bf C 51},113(2007) [Preview Abstract] |
Sunday, April 14, 2013 4:06PM - 4:18PM |
L13.00004: What do we learn from the scaling properties of azimuthal anisotropy measurements at RHIC and the LHC? Roy Lacey Azimuthal anisotropy measurements are a key ingredient in ongoing efforts to pin down the precise value of the transport coefficients of the quark gluon plasma (QGP) produced in heavy ion collisions at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). I will discuss the scaling properties of these measurements and demonstrate their utility as constraints for precision extraction of several transport coefficients. [Preview Abstract] |
Sunday, April 14, 2013 4:18PM - 4:30PM |
L13.00005: Effects of a realistic strange quark mass and color neutrality on the QCD phase diagram Philip Powell, Gordon Baym In this study we investigate the effects of an intermediate strange quark mass ($m_s$), confinement, and color neutrality on the phase structure of dense three flavor QCD by means of the Nambu--Jona-Lasinio model with Polaykov loop. Particular attention is paid to the prospects for realizing a proposed low-temperature critical point, which may allow for a smooth crossover between hadronic and color superconducting (CSC) matter at low temperatures. We analyze the decoupling of the strange quark sector from the two lighter flavors with increasing $m_s$ and also discuss the possibility of an asymmetric coupling between the Polyakov loop and quarks of different colors, which may give rise to an asymmetric CFL (ACFL) phase. Finally, we consider the effects of a local color neutrality constraint on the CSC phases which are expected at high densities, in both the equal and unequal mass cases. [Preview Abstract] |
Sunday, April 14, 2013 4:30PM - 4:42PM |
L13.00006: Results from the RHIC Beam Energy Scan Daniel Cebra In 2010 and 2011, RHIC ran a scan of several beam energies in order to map the phase boundary between hadronic and partonic matter. Au+Au collisions were studied at 200, 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV. This range of collision energies is expected to produce systems that reach chemical equilibrium at baryon chemical potentials that range from 25 to 450 MeV. At the lower end of the range of chemical potentials, the transition from partonic to hadronic matter will be a crossover, however at higher chemical potentials (possibly beyond the upper limit of the search range) the transition is expected to be first order. Studies of the RHIC beam energy scan data are searching for signatures of the first order phase transition using signals which are sensitive to the nuclear compressibility. Studies of fluctuations are being used to identify the critical point. Additionally, studies are being pursued to identify where the new phenomena seen at the highest RHIC energies and used to establish the creation of a partonic medium will turn-off. The data from this first Beam Energy Scan have defined the key search energies for these observables. RHIC is now considering a follow-up BES-II to further examine these key energies. [Preview Abstract] |
Sunday, April 14, 2013 4:42PM - 4:54PM |
L13.00007: Simulations of Statistical Model Fits to RHIC Data W.J. Llope The application of statistical model fits to experimentally measured particle multiplicity ratios allows inferences of the average values of temperatures, T, baryochemical potentials, $\mu_{\rm B}$, and other quantities at chemical freeze-out. The location of the boundary between the hadronic and partonic regions in the ($\mu_{\rm B}$,T) phase diagram, and the possible existence of a critical point, remains largely speculative. The search for a critical point using the moments of the particle multiplicity distributions in tightly centrality constrained event samples makes the tacit assumption that the variances in the ($\mu_{\rm B}$,T) values in these samples is sufficiently small to tightly localize the events in the phase diagram. This and other aspects were explored in simulations by coupling the UrQMD transport model to the statistical model code Thermus. The phase diagram trajectories of individual events versus the time in fm/$c$ was calculated versus the centrality and beam energy. The variances of the ($\mu_{\rm B}$,T) values at freeze-out, even in narrow centrality bins, are seen to be relatively large. This suggests that a new way to constrain the events on the phase diagram may lead to more sensitive searches for the possible critical point. [Preview Abstract] |
Sunday, April 14, 2013 4:54PM - 5:06PM |
L13.00008: Quark Number Fluctuations in a Chiral Model with a Magnetic Field Lidens Cheng, Vivian Incera An important consequence of quantum chromodynamics (QCD) is the existence of a phase transition between the hadronic and quark-gluon phases. The hadronic phase exhibits confinement and broken chiral symmetry. The quark-gluon phase exhibits deconfinement and chiral symmetry. The phase boundary can be seen in the temperature-quark chemical potential plane. For large chemical potential, there is a first order chiral transition. For small chemical potential and 2 massless quarks flavors, there is a second order chiral transition. Thus, a critical end point (CEP) is expected where the first order phase transitions end. In the chiral limit or for finite quark masses, the net quark number susceptibility diverges at the CEP. However, when clear from the CEP, it is finite. Hence, the net quark number susceptibility is non-monotonic along the phase boundary if there is a CEP. In this case, the Nambu--Jona-Lasinio model is composed at finite temperature and quark and isospin chemical potentials. The addition of a strong magnetic field in the model is significant because strong magnetic fields are produced in off-central heavy-ion collisions and are present at the core of neutron stars. [Preview Abstract] |
Sunday, April 14, 2013 5:06PM - 5:18PM |
L13.00009: Analysis of fixed target collisions with the STAR detector Brooke Haag Collisions between beam halo nuclei and the aluminum beam pipe allow the STAR detector at RHIC to study fixed-target Au$+$Al collisions. The injection and sub-injection energy gold beams produce Au$+$Al collisions at center-of-mass energies of 4.5, 3.5, and 3.0 GeV. These collisions allow STAR to extend the beam energy scan to lower center of mass energies and higher baryon chemical potentials than previously possible. This in turn provides a means of searching for the possible critical point to quantify the nature of the phase transition between hadronic and partonic matter. In this talk, fixed target acceptances for tracking will be discussed. Pion ratios extracted from these fixed-target collisions will be presented and compared to earlier published results from the AGS, SPS, and RHIC. [Preview Abstract] |
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