Radial flow afterburner for event generators and the baryon puzzle

A simple afterburner including radial flow to the randomized transverse momentum obtained from event generators, Pythia and Hijing, has been implemented to calculate the $p/\pi$ ratios and compare them with available data. A coherent trend of qualitative agreement has been obtained in $pp$ collisions and in $Au+Au$ for various centralities. Those results indicate that the radial flow does play an important role in the so called baryon puzzle anomaly.Comment: 11 pages, 5 figures. To appear in Journal of Physics

Evidence from Identified Particles for Active Quark and Gluon Degrees of Freedom

Measurements of intermediate pT (1.5 < pT < 5.0 GeV/c) identified particle distributions in heavy ion collisions at SPS and RHIC energies display striking dependencies on the number of constituent quarks in the corresponding hadron. One finds that elliptic flow at intermediate pT follows a constituent quark scaling law as predicted by models of hadron formation through coalescence. In addition, baryon production is also found to increase with event multiplicity much faster than meson production. The rate of increase is similar for all baryons, and seemingly independent of mass. This indicates that the number of constituent quarks determines the multiplicity dependence of identified hadron production at intermediate pT. We review these measurements and interpret the experimental findings.Comment: 8 pages, 5 figures, proceedings for SQM2006 conference in Los Angele

Strangeness Report

The paper provides a short report on strangeness production in ultrarelativistic nucleus-nucleus collision, with the main stress on strange particle abundances.Comment: Proceedings of Quark Matter 200

Bulk properties and flow

In this report, I summarize the experimental results on {\bf bulk properties and flow} presented at Quark Matter 2004. It is organized in four sections: 1) Initial condition and stopping; 2) Particle spectra and freeze-outs; 3) Anisotropic flow; 4) Outlook for future measurements.Comment: 10 pages, 4 figures, "Rapporteur-Conference Highlights", Quark Matter 2004, Oakland, January 11-1

Resonances and fluctuations of strange particle in 200 GeV Au-Au collisions

We perform an analysis of preliminary data on strange particles yields and fluctuations within the Statistical hadronization model. We begin by describing the theoretical disagreements between different statistical models currently on the market. We then show how the simultaneous analysis of yields and fluctuations can be used to differentiate between the different models, and determine if one of them can be connected to underlying physics. We perform a study on a RHIC 200 GeV data sample that includes stable particles, resonances, and the event-by-event fluctuation of the $K/\pi$ ratio. We show that the equilibrium statistical model can not describe the fluctuation, unless an unrealistically small volume is assumed. Such small volume then makes it impossible to describe the total particle multiplicity. The non-equilibrium model,on the other hand, describes both the $K/\pi$ fluctuation and yields acceptably due to the extra boost to the $\pi$ fluctuation provided by the high pion chemical potential. $\Lambda(1520)$ and $K^*$ abundance is described within error bars, but the $\Sigma^*$ is under-predicted to $\sim$ 1.5 standard deviations. We suggest further measurements that have the potential to test the non-equilibrium model, as well as gauge the effect of re-interactions between hadronization and freeze-out.Comment: References added, equations corrected. As accepted for publication by Journal of Physics

Reeconstructing Sigma0 decays in STAR

Typical comparisons of data from nuclear collisions to particle production models require a caveat for (anti)Lambda yields from experimental inability to separate the contributions of those yields from Sigma state decays. Recent analysis in STAR is leading toward resolving the contribution from excited Sigma states, but the bulk contribution comes from electromagnetic decays of the (anti)Sigma0. In the STAR detector, photon conversions into e+e- pairs in the detector material have been used to identify photons from pi0 decays. A similar technique has been used here to identify photons from (anti)Sigma0 decays in conjunction with STAR's excellent PID capabilities for finding the associated (anti)Lambda daughters. We report here on progress toward measuring the (anti)Sigma0 yields in various nuclear collisions at RHIC.Comment: 8 pages, 5 figures, proceedings of Hot Quarks 2004 workshop, submitted to J. Phys.

STAR results on medium properties and response of the medium to energetic partons

We report new STAR results on the consequences of highly energetic partons propagating through the medium formed in heavy ion collisions using correlations as an experimental probe. The recent results providing insights about color factor effects and path length dependence of parton energy loss, system size dependence of di-hadron fragmentation functions, conical emission and ridge formation in heavy ion collisions are presented.Comment: STAR Plenary talk at QM2008. Manuscript for the Proceedings of Quark Matter 2008, Jaipur, Indi

K∗(892)K^{*}(892) Production in Au+Au and pp Collisions at sNN\sqrt{s_{NN}} = 200GeV at STAR

Mid-rapidity $K^{*0}(892)\to K\pi$ and $K^{*\pm}(892)\to K_S^0\pi^{\pm}$ are measured in Au+Au and pp collisions at $\sqrt{s_{NN}}$=200GeV using the STAR detector at RHIC. The $K^{*0}(892)$ mass is systematically shifted at small transverse momentum for both Au+Au and pp collisions. The $K^{*0}(892)$ transverse mass spectra are measured in Au+Au collisions at different centralities and in pp collisions. The $K^{*0}(892)$ mean transverse momentum as a function of the collision centrality is compared to those of identified $\pi^{-}$, $K^{-}$ and $\bar{p}$. The $K^{*}/K$ and $\phi/K^{*}$ ratios are compared to measurements in A+A, $pp$, $\bar{p}p$, $e^{+}e^{-}$ collisions at various colliding energies. The physics implications of these measurements are also discussed.Comment: 6 pages, 4 figures, proceedings of Strange Quarks in Matter (SQM2003), Atlantic Beach, USA, to be published in J. Phys.

Particle Ratios and the QCD Critical Temperature

We show how the measured particle ratios at RHIC can be used to provide non-trivial information about the critical temperature of the QCD phase transition. This is obtained by including the effects of highly massive Hagedorn resonances on statistical models, which are used to describe hadronic yields. Hagedorn states are relevant close to $T_c$ and have been shown to decrease $\eta/s$ to the KSS limit and allow for quick chemical equilibrium times in dynamical calculations of hadrons. The inclusion of Hagedorn states creates a dependence of the thermal fits on the Hagedorn temperature, $T_H$, which is assumed to be equal to $T_c$, and leads to an overall improvement of thermal fits. We find that for Au+Au collisions at RHIC at $\sqrt{s_{NN}}=200$ GeV the best square fit measure, $\chi^2$, occurs at $T_c \sim 176$ MeV and produces a chemical freeze-out temperature of 170.4 MeV and a baryon chemical potential of 27.8 MeV.Comment: 6 pages, 2 figures, talk presented at the International Conference on Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - oct. 2, 200

ρ(770)0\rho(770)^0, K∗(892)0^*(892)^0 and f0(980)_{0}(980) Production in Au-Au and pp Collisions at sNN\sqrt{s_{NN}} = 200 GeV

Preliminary results on $\rho(770)^0 \to \pi^{+}\pi^{-}$, K$^{*}(892)^{0} \to \pi$K and $f_{0}(980) \to \pi^{+}\pi^{-}$ production using the mixed-event technique are presented. The measurements are performed at mid-rapidity by the STAR detector in $\sqrt{s_{NN}}$= 200 GeV Au-Au and pp interactions at RHIC. The results are compared to different measurements at various energies.Comment: 4 pages, 6 figures. Talk presented at Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A