Entropy production by resonance decays

We investigate entropy production for an expanding system of particles and resonances with isospin symmetry -- in our case pions and $\rho$ mesons -- within the framework of relativistic kinetic theory. A cascade code to simulate the kinetic equations is developed and results for entropy production and particle spectra are presented.Comment: 17 pages, 10 ps-figures included, only change: preprint number adde

A systematic comparison of jet quenching in different fluid-dynamical models

Comparing four different (ideal and viscous) hydrodynamic models for the evolution of the medium created in 200 AGeV Au-Au collisions, combined with two different models for the path length dependence of parton energy loss, we study the effects of jet quenching on the emission-angle dependence of the nuclear suppression factor R_AA(phi) and the away-side per trigger yield I_AA(phi). Each hydrodynamic model was tuned to provide a reasonable description of the single-particle transverse momentum spectra for all collision centralities, and the energy loss models were adjusted to yield the same pion nuclear suppression factor in central Au-Au collisions. We find that the experimentally measured in-plane vs. out-of-plane spread in R_AA(phi) is better reproduced by models that shift the weight of the parton energy loss to later times along its path. Among the models studied here, this is best achieved by energy loss models that suppress energy loss at early times, combined with hydrodynamic models that delay the dilution of the medium density due to hydrodynamic expansion by viscous heating. We were unable to identify a clear tomographic benefit of a measurement of I_AA(phi) over that of R_AA(phi).Comment: 17 pages, 11 figure

Ω−\Omega^- and Ωˉ+\bar\Omega^+ production in Au+Au collisions at sNN\sqrt{s_{NN}} = 130 and 200 GeV

Mid-rapidity Omega and anti-Omega production in Au+Au collisions at RHIC is studied with the STAR experiment. We report preliminary results on yields and spectra at $\sqrt{s_{NN}}$ = 130 and 200 GeV. Production relative to negatively charged hadrons (h-) as well as thermal freeze-out and collective expansion are discussed.Comment: 4 pages, 5 figures, 1 table, Contribution to Quark Matter 2002, Nantes, France, July 200

Source Parameters from Identified Hadron Spectra and HBT Radii for Au-Au Collisions at sqrt(s_NN)=200 GeV in PHENIX

The characteristics of the particle emitting source are deduced from low transverse momentum identified hadron spectra (transverse mass less than 1 GeV) and HBT radii using a hydrodynamic interpretation. From the most peripheral to the most central data, the single particle spectra are fit simultaneously for all pions, kaons, and (anti-)protons using the parameterization in [1] and assuming a linear transverse flow profile. Within the systematic uncertainties, the expansion parameters called the freeze-out temperature and flow velocity, respectively decrease and increase with the number of participants, saturating for both at mid-centrality. The expansion using analytic calculations of the kT dependence of HBT radii in [2] is fit to the data but no chi-squared minimum is found.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

Thermal Equilibration and Expansion in Nucleus-Nucleus Collision at the AGS

The rather complete data set of hadron yields from central Si + A collisions at the Brookhaven AGS is used to test whether the system at freeze-out is in thermal and hadro-chemical equilibrium. Rapidity and transverse momentum distributions are discussed with regards to the information they provide on hydrodynamic flow.Comment: 11 pages + 2 uuencoded figure

Particle production at very low and intermediate transverse momenta in d+Au and Au+Au collisions

The transverse momentum spectra of identified charged particles have been measured at very low and intermediate transverse momenta in Au+Au collisions at sqrt(s_NN) = 62.4 GeV and d+Au collisions at sqrt(s_NN) = 200 GeV using the PHOBOS detector at RHIC. New results on charged particle production at very low p_T in central Au+Au collisions at sqrt(s_{NN) = 200 GeV in the centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-p_T data with predictions of a recent optical model is shown. The shapes of m_T spectra for d+Au and Au+Au collisions are compared.Comment: Presented at the 18th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2005, Budapest, Hungary, Aug. 4-9, 200

Probing bulk properties and partonic collectivity via multi-strange baryons in Au+Au collisions at top RHIC energy

The study of the multi-strange production in the final state of ultra-relativistic Au+Au collisions at top RHIC energy gives information on the freeze-out conditions and probably on earlier stages of the collision. The chemical freeze-out temperature as well as the strangeness phase space occupancy factor gamma_s extracted from statistical models are studied as a function of the collision centrality. Within the framework of a hydrodynamically-inspired model the transverse collectivity of the collision is investigated. In this view, multi-strange particles seem to develop significant radial transverse flow. Furthermore, they present an elliptic flow as stronger as previously measured baryons supporting the idea that a fraction of the final collective motion has been developed at an early partonic stage of the collision.Comment: 5 pages, 4 figures. Talk presented in Phase transitions in strongly interacting matter Prague, 23.8.-29.8. 2004 18th Nuclear Physics Division Conference of the EPS (NPDC18) Europhysics Conferenc

Results on Identified Hadrons from the PHENIX Experiment at RHIC

Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied. The transverse flow velocity and freeze-out temperature are extracted from $p_{T}$ spectra within the framework of a hydrodynamic collective flow model. Two-particle HBT correlations for charged pions are measured in different centrality selections for a broad range of transverse momentum of the pair. Results on elliptic flow measurements with respect to the reaction plane for identified particles are also presented.Comment: 10 pages, 10 figures. Talk presented at Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

Two-particle interferometry for non-central heavy-ion collisions

In non-central heavy ion collisions, identical two particle Hanbury-Brown/Twiss (HBT) correlations C(K,q) depend on the azimuthal direction of the pair momentum K. We investigate the consequences for a harmonic analysis of the corresponding HBT radius parameters. Our discussion includes both, a model- independent analysis of these parameters in the Gaussian approximation, and the study of a class of hydrodynamical models which mimic essential geometrical and dynamical properties of peripheral heavy ion collisions. Also, we discuss the additional geometrical and dynamical information contained in the harmonic coefficients of these HBT radius parameters. The leading contribution of their first and second harmonics are found to satisfy simple constraints. This allows for a minimal, azimuthally sensitive parametrization of all first and second harmonic coefficients in terms of only two additional fit parameters. We determine to what extent these parameters can be extracted from experimental data despite finite multiplicity fluctuations and the resulting uncertainty in the reconstruction of the reaction plane.Comment: 14 pages, RevTeX, 7 eps-figures include