Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session H13: Ultrarelativistic Heavy Ion Collisions II: Theory |
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Sponsoring Units: DNP Chair: Ralf Rapp, Texas A&M University Room: Marriott Tampa Waterside Room 12 |
Sunday, April 17, 2005 8:30AM - 8:42AM |
H13.00001: Centrality Dependence of Bulk Fireball Properties at RHIC Johann Rafelski, Jean Letessier, Giorgio Torrieri We explore the centrality dependence of properties of the dense hadronic matter created in \mathversion{bold}{$\sqrt{s_{NN}}=200$}\,GeV Au--Au collisions at RHIC. Using the statistical hadronization model we fit particle yields known for 11 PHENIX centrality bins and using STAR yields for $\phi$ and $K^*$. We present the resulting centrality dependence of model parameters $T,\mu_{\rm B},\mu_{\rm S}, $\gamma_s$, the rapidity yields of physical quantities and the physical properties of bulk matter at hadronization. The most remarkable finding of this study is the recognition that the bulk properties $P$ pressure, $\epsilon$ energy density, $\sigma$ of the hadronizing dense matter fireball created at RHIC do not depend on the size of the system for $A\gtrsim 20 $, where $A$ is the number of reaction participants. For most central collisions the strangeness per entropy yield $s/S=(2.9\pm0.3)10^{-3}$ is more than 4 times enhanced compared to the AGS energy scale. For the most peripheral reactions this ratio is $s/S=(1.9\pm0.3)10^{-3}$ which shows the influence of the fireball expansion dynamics on production of strangeness. We see this in the steady rise of strangeness occupancy $\gamma_s$ with centrality. The baryon end entropy density per unit rapidity grows also with centrality and we find in most central 5\% collisions $d(B-\overline B)/dy=14\pm2$, the strangeness yield $ds/dy=135\pm10$ and the entropy yield $dS/dy=4900\pm400$. [Preview Abstract] |
Sunday, April 17, 2005 8:42AM - 8:54AM |
H13.00002: Particle Production and Bulk Fireball Properties in \mathversion{bold}{$\sqrt{s_{NN}}=130$} and 200 GeV Au--Au Collisions Giorgio Torrieri, Jean Letessier, Johann Rafelski We study within the statistical hadronization model the fireball of matter created at RHIC in 5\% most central $\sqrt{s_{\rm NN}}=130$ and 200 GeV Au--Au collisions. We evaluate six model variants: chemical equilibrium, strange quark non-equilibrium, and general flavor yield non-equilibrium where in each case we study hadronic resonances with, and without a width weight. The broad data set we consider includes most stable particles and many short-lived resonances. The precision of the best fit for both stable and unstable hadrons is comparable, with resonances considerably reducing the fitted parameter error. The statistical significance analysis favors an over saturated quark abundance. We determine collision energy dependence of rapidity yields of energy, strangeness, entropy, baryon number, and of physical properties. We search for universal thermal bulk properties that do not vary with collision energy. The bulk properties of the hadronizing fireball, as well as features of the equation of state are remarkably collision energy-independent, suggesting that the system's degrees of freedom and freeze-out conditions do not vary between $\sqrt{s_{\rm NN}}=130$ and 200. We show that consideration of certain experimental resonance yields allows a great enhancement in precision of our analysis outcome. [Preview Abstract] |
Sunday, April 17, 2005 8:54AM - 9:06AM |
H13.00003: Deconfinement energy threshold: analysis of hadron yields at 11.6 \mathversion{bold}$A$ GeV Jean Letessier, Johann Rafelski, Giorgio Torrieri We analyze within the statistical hadronization model the totality of $4\pi$-hadron yields obtained at the AGS in the range 11--11.6 $A$ GeV, including in the analysis the recently reported $\phi$, and the indirectly evaluated $\overline\Lambda/\bar p$. Allowing for the chemical non-equilibrium at hadronization, and introduction into the study of (multi)strange hadrons are the key ingrediants of the analysis pointing to possible deconfinement at top AGS reaction energy scale. The high observed $\phi/K^+$ yield pushes the chemical freeze-out condition to $T=142\pm3$ MeV and $\mu_{\rm B}=708\pm 60$ MeV while the quark phase space is found to be greatly undersaturated, with $\gamma_q=0.35\pm0.27$ and $\gamma_s-0.23\pm0.18$. We find that strangeness per entropy $s/S<0.075$ in relevant chemical conditions, including equilibrium. This is nearly 4 times lower than at RHIC. We study multistrange particle ratios of interst to future experimental studies of low energy deconfinement. [Preview Abstract] |
Sunday, April 17, 2005 9:06AM - 9:18AM |
H13.00004: Nuclear modifications and parton fragmentation functions in d+Au collisions Adeola Adeluyi, George Fai We compare nuclear modification factors calculated with different shadowing parameterizations and different fragmentation functions to each other and to BRAHMS data. This is important to assess the robustness of perturbative QCD (pQCD) calculations and the ability of various models to describe tha data. Calculations based on the Color Glass Condensate picture and on $k_T$-factorized pQCD models were checked against these data by different groups earlier. We find that the applied fragmentation function parameterizations have a significant effect on the results, while shadowing parameterizations and parton distribution functions have relatively little effect. The role of different deuteron wave functions is also studied. Unfortunately, the reach of available data in $p_T$ has little overlap with the region where pQCD is applicable. The difference between the data and pQCD calculations becomes more pronounced at forward rapidities. [Preview Abstract] |
Sunday, April 17, 2005 9:18AM - 9:30AM |
H13.00005: Photon Elliptic Flow and Jet Photon Correlations in Heavy Ion Collisions Rainer Fries It has been shown that jets interacting with the medium in high energy heavy ion collisions are a bright source of photons at intermediate transverse momentum. We study this jet photon conversion process in detail and show that these photons exhibit an elliptic azimuthal asymmetry $v_2$ which is negative with respect to the $v_2$ of hadrons. We also investigate photon-jet correlations and the implications of the jet photon conversion process for studies of energy loss with photon-tagged jets. [Preview Abstract] |
Sunday, April 17, 2005 9:30AM - 9:42AM |
H13.00006: Pionic interferometry in RHI Collisions Gerald A. Miller, John G. Cramer We explain and apply our chiral treatment of pionic interactions with the medium, nucl-th/0411031. The previous analysis of STAR data which found evidence for the presence of a chiral phase transition is extended to include the data of NA49, taken at lower energy. Our preliminary results are that all of the data for radii and pionic spectra can be explained using the same approach, and that the medium's influence is characterized as a strong attraction combined with a moderate amount of absorption. The inferred size of the system grows as the energy is increased. We also analyze the complete correlation function to determine if measurements of other observables could further test our theory. [Preview Abstract] |
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