Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session H7: Relativistic Heavy Ion Collisions II |
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Sponsoring Units: DNP Chair: Zhangbu Xu, Brookhaven National Laboratory Room: Grand E |
Sunday, May 1, 2011 10:45AM - 10:57AM |
H7.00001: Study of $\Lambda-\Lambda$ correlations with the STAR detector at RHIC Neha Shah Considerable experimental efforts have been devoted to search for the existence of dibaryon H, a six quark state, proposed by Jaffe [1]. It has also been proposed that the H particle would appear as a bump in the $\Lambda-\Lambda$ invariant mass spectra if the H is a resonance state, or the H would lead to a depletion of the $\Lambda-\Lambda$ correlation near the threshold if the H is weakly bound. In this scenario, the mass of H is expected to be in the range (2230, 2380) MeV. Because of high rate of strange particle production per heavy ion collision RHIC is a unique place to search for the H. The $\Lambda-\Lambda$ correlation measurements at RHIC are sensitive to their mutual interactions, which can be used to probe whether there is a stable H particle or H resonance. This sensitivity is unique at RHIC because of the source size for $\Lambda$ production and the allowed range of $\Lambda-\Lambda$ scattering parameters in nucleus-nucleus collisions. We present the measurement of $\Lambda-\Lambda$ correlations in Au+Au collisions at $\sqrt{s}=39$GeV using the STAR experiment at RHIC. \\[4pt] [1] R. L. Jaffe, Phys. Rev. Lett. 38, 195 (1977). [Preview Abstract] |
Sunday, May 1, 2011 10:57AM - 11:09AM |
H7.00002: System Size Dependence of Chemical and Kinetic Freeze-Out in Heavy Ion Collisions Orpheus Mall Heavy Ion collisions have been performed at RHIC with Cu and Au nuclei to date. The two systems differ in initial energy density and provide further understanding of the quark matter phase diagram. A statistical thermal model study of charged hadron ratios provides chemical freeze-out properties of the two systems. Boltzmann blast-wave studies of the two systems at top RHIC energies show that the kinetic freeze-out properties scale with total charged multiplicity at midrapidity. We present results from two low energy runs at RHIC in Au+Au collisions at 19.6 GeV and Cu+Cu collisions at 22.4 GeV. Particle spectra for $\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ are studied as a function of $(m_{T}-m_{0})$ up to $\sim$1 GeV measured using ionization energy loss in the STAR Time Projection Chamber. We report the chemical freeze-out temperature $T_{ch}$ vs. the baryon chemical potential $\mu_{B}$, and the kinetic freeze-out temperature $T_{kin}$ vs. the blast velocity $<\beta_{T}>$, and other results. Our results are compared with RHIC data at various energies and world data. [Preview Abstract] |
Sunday, May 1, 2011 11:09AM - 11:21AM |
H7.00003: Particle Production in $s_{\small NN} = 2.76$ TeV Heavy Ion Collisions Johann Rafelski, Jean Letessier We consider, within the statistical hadronization model (SHM), the near central rapidity $y\simeq 0$ integrated hadron yields expected at LHC $\sqrt{s_{\rm NN}} = 2.76$ TeV ion reactions, for which the total charged hadron rapidity most central head-on collision yield is $dh/dy|_{y=0}\simeq 1800$\,. For the chemical equilibrium SHM, we discuss composition of $dh/dy$ as function of hadronization temperature. For chemical non-equilibrium SHM, we input the computed specific strangeness yield $s/S$, demand explosive disintegration and study the QGP break up as a function of the critical hadronization pressure $P$. We develop observables distinguishing the hadronization models and conditions. We show the enhanced yield of strangeness and the related enhancement of (multi) strange particles. We find compared with the RHIC energy range a three times enhanced hadronization volume $dV/dy \simeq 4500$ fm$^3$ indicating corresponding changes in the HBT observables. The local rest frame thermal energy content $dE/dy|_0 = 2$ TeV constrains hydrodynamic models. A large yield of $\pi^0$, $\eta$ and thus of associated decay photons is noted, enhanced somewhat in the.chemical non-equilibrium case. [Preview Abstract] |
Sunday, May 1, 2011 11:21AM - 11:33AM |
H7.00004: Unstable Hadrons in Hot Hadron Gas in Laboratory and in the Early Universe Inga Kuznetsova, Johann Rafelski We study kinetic master equations for reactions involving the formation and the natural decay of unstable particles in a thermal expanding hadronic gas in the laboratory and in the early Universe. We consider here for the first time the role of the decay channel of one (hadron resonance) into two daughter particles, and also by token of detailed balance the inverse process, fusion of two (thermal) particles into one. We obtain the thermal invariant reaction rate using as an input the free space (vacuum) decay time and show the medium quantum effects on $\pi+\pi \leftrightarrow \rho$ reaction relaxation time. As another laboratory example we describe the K+K$\leftrightarrow\phi$ process in thermal expanding hadronic gas in heavy ions collisions. A particularly interesting application of our formalism is the $\pi^0\leftrightarrow \gamma +\gamma $ process in the early Universe. We also explore the fate of charged pions and the muon freeze-out in the Universe. Another interesting field of application of our formalism is the study of short lived hadronic resonances, which are in general not able to reach yield equilibrium. We study the evolution of hadron resonances in small drops of QGP and use the insight gained to generalize the dynamics to QED effects as well. [Preview Abstract] |
Sunday, May 1, 2011 11:33AM - 11:45AM |
H7.00005: Lambda(1520) production in Cu+Cu collisions at $\sqrt{s_{NN}} = 200$ GeV in STAR Masayuki Wada Due to their short life-time ($\sim$fm/c), hadronic resonances provide information on the hadronic medium between chemical and kinetic freeze-out via the processes of re-generation and re-scattering of the decay particles. Previous studies have showed a suppression of the $\Lambda^{*}/\Lambda$ and $K^{*}/K$ ratios in Au+Au collisions relative to p+p collisions at $\sqrt{s_{NN}} = 200$ GeV. The magnitude of this suppression indicates the system time span between the two freeze-outs. The onset of this suppression occurs in the region of 2-100 participating nucleons (peripheral collisions), and remains constant thereafter. The Cu+Cu system is therefore important because it provides us with a smaller system to study more precisely the onset of suppression. We present the first measurement of $\Lambda$(1520) mass spectra and yields via hadronic channel, $\Lambda^{*}\rightarrow p+K$, at midrapidity in Cu+Cu collisions at $\sqrt{s_{NN}} =200$GeV using the STAR experiment at RHIC. [Preview Abstract] |
Sunday, May 1, 2011 11:45AM - 11:57AM |
H7.00006: Strange Antibaryon to Baryon Ratios in RHIC Beam Energy Scan Feng Zhao In statistical thermal model, the yields of strange baryons can be described by the Boltzmann distribution approximately and the yields only depend on baryon chemical potential ($\mu_{B}$) and temperature of the system ($T$), which vary with the collision energy. From the analysis of particle yield ratios, one can obtain reliable information on chemical freeze-out parameters of the hadronic final state. STAR took data at beam energies of 7.7~GeV, 11.5~GeV and 39~GeV in AuAu collisions at RHIC in 2010. In our analysis, we measure the antibaryon to baryon ratios for the three energies, and compare our results with statistical thermal model to obtain the information of the temperature and the baryon chemical potential. [Preview Abstract] |
Sunday, May 1, 2011 11:57AM - 12:09PM |
H7.00007: Status Report on Anti-$\alpha$ Search at STAR Hao Qiu In high-energy nuclear collisions, unlike the early universe microseconds after the Big Bang, the relatively short-lived expansion makes it possible for antimatter to decouple quickly from matter. This makes a high-energy accelerator facility the ideal environment for producing and studying heavy species of antimatter. The heaviest antimatter previously observed are A=3 antimatter (anti-Helium3, anti-triton and anti-hypertriton). During the RHIC 200 GeV Au-Au beam period in 2010, the STAR detector operated with high luminosities and high data taking rates. This, together with an excellent particle identification based on the Time Projection Chamber and the newly installed Time of Flight detector, puts STAR in a good position to search for anti-$\alpha$ particles (anti-He4). To cope with the large data volume in 2010 and to speed up the search effort, a High Level online tracking Trigger (HLT) was implemented to reconstruct events online and tag rare events with great physics interest. In this talk, we present STAR's HLT capabilities, as well as the status of the anti-$\alpha$ search with the data taken by the HLT in 2010. [Preview Abstract] |
Sunday, May 1, 2011 12:09PM - 12:21PM |
H7.00008: STAR as a Fixed Target Experiment Samantha Brovko Analysis of fixed target collisions between gold ions in the beam and aluminum nuclei in the beam pipe using the STAR detector at RHIC will be presented. These fixed target collisions allow us to study a region of collision energy below the lowest energy scheduled for the RHIC beam energy scan. This might extend the baryon chemical potential region available for discovery of the critical point along the hadronic gas to quark-gluon plasma boundary in the nuclear matter phase diagram. In this talk, we will show preliminary results of pion, proton and light nuclei spectra as well as dN/dy distributions for pions and protons. Comparisons will be made to results from the AGS heavy ion program and to UrQMD simulations. [Preview Abstract] |
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