Ξ−\Xi^{-} and Ξˉ+\bar{\Xi}^{+} baryon production in Au+Au collisions at sNN=130\sqrt{s_{NN}}=130 GeV

We report preliminary results on the centrality dependence of the $\Xi^{-}$ and $\bar{\Xi}^{+}$ production at mid-rapidity in $\sqrt{s_{NN}}=130$ GeV Au+Au collisions from the STAR experiment. For the most central data the obtained yields suggest a saturation of strangeness production per produced hadron. The calculated inverse slope parameter may indicate an earlier freeze-out of these particles.Comment: 4 pages, 3 figures, 1 table, Contribution to Quark Matter 2002, Nantes, France, July 200

Multi-strange particle production in relativistic heavy ion collisions at sNN=62.4\sqrt{s_{NN}}=62.4 GeV

We present preliminary STAR results on measurements of multi-strange particles $\Xi$, $\Omega$ and their anti-particles from Au+Au and Cu+Cu at $\sqrt{s_{NN}}=62.4$ GeV collisions. In order to better understand the role of strangeness enhancement in nucleus-nucleus collisions and its scaling properties with system size, we compare the results from Au+Au and Cu+Cu reactions for different event centrality classes. Strangeness enhancement is discussed in the context of multi-strange to pion ratios. Finally, $\Omega/\phi$ ratio is shown for different systems and energies for a systematic study

System and Energy Dependence of Strangeness Production with STAR

The yields and spectra of strange hadrons have each been measured by STAR as a function of centrality in $\rm \sqrt{s_{NN}}=$ 200 GeV AuAu collisions. By comparison to measurements in pp and dAu at $\rm \sqrt{s_{NN}}=200$ GeV and in AuAu at $\rm \sqrt{s_{NN}}=62$ GeV the dependence on system size and energy is studied. Short-lived resonances, such as $\Sigma (1385)$ and $\Lambda (1520)$, that may decay and regenerate in the medium, are used to examine the dynamical evolution between production and freeze-out for these systems. Particle production is investigated by comparison to thermal models, which assume a simple scaling of the yield with $\rm N_{part}$, in order to calculate the strangeness enhancement. Our hyperon measurements in AuAu indicate that $\rm N_{bin}$ may be a more appropriate scale for the strangeness correlation volume. In this case canonical suppression can not be simply parameterized with the geometrical overlap volume but will depend on the individual quark content of each particle. This theory is tested by comparing the data from different collision systems and centralities.Comment: Quark Matter 2005 Talk. Talk ppt file with further supporting plots can be found in http://qm2005.kfki.hu/talk2_select.pshtml?sel=10

Strangeness production within Parton-Hadron-String Dynamics (PHSD)

The Parton-Hadron-String Dynamics (PHSD) transport approach consistently simulates the full evolution of a relativistic heavy-ion collision from the initial hard scatterings string formation through the dynamical deconfinement phase transition to the quark gluon plasma (QGP), to the hadronization and to subsequent interactions in the hadronic phase. The transport theoretical description of quarks and gluons is based on a dynamical quasiparticle model for partons matched to reproduce recent lattice QCD results in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks). Studying Pb+Pb reactions from 40 to 158 A GeV, we find that at most 40% of the collision energy is stored in the dynamics of the partons. This implies that a large fraction of non-partonic, i.e. hadronic or string-like matter, which can be viewed as a hadronic corona, is present in these reactions, thus neither hadronic nor purely partonic models can be employed to extract physical conclusions in comparing model results with data. On the other hand, comparing the PHSD results to those of the Hadron-String Dynamics (HSD) approach without the phase transition to QGP, we observe that the existence of the partonic phase has a sizeable influence on the transverse mass distribution of final kaons due to the repulsive partonic mean fields and initial partonic scattering. Furthermore, we find a significant effect of the QGP on the production of multi-strange antibaryons due to a slightly enhanced s+sbar pair production in the partonic phase from massive time-like gluon decay and to a more abundant formation of strange antibaryons in the hadronization process.Comment: Talk given at the International Conference Strangeness in Quark Matter 2009 (SQM 09

A study of the pi^0pi^0 system produced in charge exchange and central collisions

A study of the $\pi^0\pi^0$ system produced in charge exchange $\pi^-p$ collisions at 38 and 100 GeV/c and in central $pp$ interactions at 450 GeV/c has been carried out. The $S$ wave has rather a complicated structure in both processes indicating the existence of several scalar resonances. The $f_0(980)$ and $f_0(1500)$ appear as dips at 1 and 1.5 GeV in the $S$ wave for charge exchange reaction, and as shoulders at these masses in the $S$ wave for central production. The production of the $f_0(980)$, $f_0(1300)$ and $f_0(1500)$ in the reaction $pp \to p_f\pi^0\pi^0p_s$ as a function of the $dP_{T}$ kinematical filter shows the behaviour differed from what has been observed for the undisputed $q\bar{q}$ mesons. An extra $f_0(2000)$ state is seen in the $S$ wave for charge exchange reaction as a dip at 2 GeV. Resonances with higher spins, $f_2(1270)$, $f_4(2050)$ and $f_6(2510)$, have also been studied. All the three mesons are produced in the reaction $\pi^-p\to\pi^0\pi^0{n}$ mainly via an one-pion exchange for small $-t$, whereas a natural-parity exchange domimates for large $-t$. The behaviour of the centrally produced $f_2(1270)$ as a function of the $dP_{T}$ is consistent with what has been observed for other $q\bar{q}$ states.Comment: 6 pages, 6 figures, use file stwol.sty, presented at International High-Energy Physics Euroconference in Quantum Chromodynamics, 2-8 July 1998, Montpellier, France on behalf of the GAMS and WA102 Collaboration

Heavy-Ion Physics with ALICE

The ALICE detector, expected to start operating at the Large Hadron Collider this year, was designed specifically for the study of heavy-ion collisions. In this paper we recall the main features of the apparatus and give some examples of the expected physics performance

Strangeness Production at SIS measured with HADES

n this paper we review the recent results on strangeness production measured by HADES in the Ar+KCl system at a beam energy of 1.756 AGeV. A detailed comparison of the measured hadron yields with the statistical model is also discussed.Comment: submitted to Nucl. Phys. A, Proceedings of the 10th International Conference on Nucleus-Nucleus Collision, Beijing China 200

Strange hadron resonances as a signature of freeze-out dynamics

We study the production and the observability of Lambda*(1520), K*0(892), and Sigma*(1385), strange hadron resonances as function of the freeze-out conditions within the statistical model of hadron production. We obtain an estimate of how many decay products are rescattered in evolution towards thermal freeze-out following chemical freeze-out, and find that the resonance decay signal is strong enough to be detected. We show how a combined analysis of at least two resonances can be used to understand the chemical freeze-out temperature, and the time between chemical and thermal freeze-outs.Comment: 6 pages including figures; added references, revised two paragraphs on meson cross sections, submitted to Phys. Lett.