Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session D10: Relativistic Heavy Ions I |
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Sponsoring Units: DNP Chair: Senta Greene, Vanderbilt University Room: Embassy A |
Saturday, March 31, 2012 3:30PM - 3:42PM |
D10.00001: The axial anomaly and three-flavor NJL model with confinement: constructing the QCD phase diagram Philip Powell, Gordon Baym We investigate the phase structure of massless three-flavor QCD by extending the Nambu--Jona-Lasinio model to include the effects of confinement and the axial anomaly. We study the interplay between the chiral and diquark condensates induced by the axial anomaly, as well as their relationship with the Polyakov loop, which parameterizes confinement. By minimizing the thermodynamic potential we construct the QCD phase diagram and investigate the possibility of realizing a recently discovered low temperature critical point and an associated BEC-BCS crossover. We also perform a Ginzburg-Landau expansion of the thermodynamic potential, comparing our results to a prior analysis based purely on symmetry considerations, in order to assess the lowest-order effects of the condensate-confinement couplings. [Preview Abstract] |
Saturday, March 31, 2012 3:42PM - 3:54PM |
D10.00002: Measurement of high-pt azimuthal anisotropy in charged hadron production from 2.76 TeV PbPb collisions at CMS Victoria Zhukova The CMS experiment has measured the azimuthal anisotropy of charged hadrons over a very broad transverse-momentum range in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 $TeV$ and for multiple collision centralities. The second order Fourier coefficient, $v_{2}$, is extracted by correlating charged tracks with the event plane reconstructed using the energy deposited in the forward-angle calorimeters. Utilizing the broad coverage of the CMS calorimetry at the very forward region, contamination from back-to-back dijets is significantly suppressed. The observed azimuthal anisotropy in the high-pt regime provides important constraints on the path-length dependence of parton energy loss. [Preview Abstract] |
Saturday, March 31, 2012 3:54PM - 4:06PM |
D10.00003: Decays of the rho mesons--a neglected source of low-mass dileptons? Peter Lichard The production of dileptons is considered an important tool in the diagnosis of strongly interacting matter created in ultra-relativistic heavy-ion collisions. Some experiments observed an excess of the low-mass dileptons over the expectation represented by the ``cocktail'' composed of the contributions from decays of the free-streaming hadrons leaving the interaction region. We show that at least a part of the effect may be caused by underestimating the rho-meson component in the ``cocktail.'' [Preview Abstract] |
Saturday, March 31, 2012 4:06PM - 4:18PM |
D10.00004: Determining the uncertainty on the charm cross section and the effect on the $J/\psi$ cross section Randy Nelson, Ramona Vogt, Anthony Frawley Theoretical estimates of charm production cross sections are strongly dependent on the mass and scale choices. The particular choice defining the ``central value'' and the limits on the mass and scale parameters are of crucial importance in comparing calculations to the experimental data. Previous Fixed Order Next-to-Leading-Log (FONLL) calculations have used a standard fiducial set of parameters. Here we explore the available parameter space in charm quark mass, renormalization and factorization scales that give reasonable fits to the total charm cross section at next-to-leading order in perturbative QCD to make a revised estimate of its uncertainty. We study the effect of the parameter choices on the charm differential cross sections, extrapolated to LHC energies, as well as the effect of these parameter choices on the $J/\psi$ production cross section calculated in the color evaporation model. [Preview Abstract] |
Saturday, March 31, 2012 4:18PM - 4:30PM |
D10.00005: J/Psi Analysis in Ultra Peripheral Collisions at Relativistic Heavy Ion Collider with STAR Dilan Madagodahettige Don Relativistic heavy ions carry strong transverse electromagnetic fields which can be treated as sources of quasi-real virtual photons. The ions interact through photon-Pomeron and photon-photon collisions at impact parameter more than twice the nuclear radius, so hadronic interactions are suppressed. We present recent results of the STAR experiment at RHIC measurement of $J/\psi$ photoproduction in 200 (GeV) AuAu collisions at RHIC. The $p_{T}$ distribution of the $J/\psi$ mesons peaks at very low $p_{T}$, consistent with expectations for coherent photoproduction. Both the photoproduction cross section and the $J/\psi$ rapidity distribution are expected to show the effects of gluon shadowing. The distribution of rapidity within $\mid y \mid < 1$ for the $J/\psi$ mesons are also presented. [Preview Abstract] |
Saturday, March 31, 2012 4:30PM - 4:42PM |
D10.00006: Spatial correlation functions in lattice QCD and quarkonium properties at high T Peter Petreczky I will discuss lattice QCD calculations of Wilson loops at finite temperature and the extraction of the temperature dependent heavy quark potential from them. I will also discuss spatial charmonium correlators calculated in 2+1 flavor lattice QCD and their implications on charmonium melting in the deconfined phase. [Preview Abstract] |
Saturday, March 31, 2012 4:42PM - 4:54PM |
D10.00007: Photons from Spectators in Relativistic Heavy-Ion Reactions Edwin Norbeck, Yasar Onel There are two very different regimes in the relativistic collision of two large nuclei. The overlap region becomes a quark-gluon plasma. The parts of the nuclei that do not interact continue on in the original direction as spectators. With a large overlap (small impact parameter) the spectators are completely disintegrated into their constituent nucleons. It is to be expected that the disintegration will result in the production of many photons. As the impact parameter increases, an increasing number of nucleons remain bound as small nuclei, usually in some excited state. There will be photons from the deexcitation of the small nuclei. It will be most interesting to study the evolution of the photon spectrum as the impact parameter is increased. At an LHC collision energy of 5.5 TeV/nucleon the Lorentz transformation puts half of the photons into a cone with a half angle of only 0.34 mrad, which is 4.8 cm from the center line at a distance of 140 m from the interaction point. This fits into the 10 cm wide clear space between the incoming and outgoing beam pipes. The nuclear energy photons are boosted in energy by a factor of 2926 at the edge of the cone and twice as much in the center. The impact parameter can be measured by counting the number of spectator neutrons. The photon detector must avoid the spectator neutrons, which at 140 m are all in a spot of radius less than one cm. [Preview Abstract] |
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