Recent Results on Strangeness Production at RHIC

Due to its large acceptance, the STAR experiment has acquired a wealth of data on strangeness production for a variety of collisions systems and energies, from p+p to Au+Au. By using the yields and spectra, we address the evolution of the bulk system, including strangeness enhancement and the flavour dependence of radial and elliptic flow. Utilising the fact that we can identify strange baryons and mesons, we investigate different hadronization mechanisms in the intermediate and high p$_{T}$ regions. The ratios of the particle yields, measured to high p$_{T}$, are used to further investigate the range and applicability of the previously reported anomalous baryon production. We also study two-particle azimuthal correlations of identified particles in order to investigate any flavour dependence of jet fragmentation in the available p$_{T}$ range. Data was presented for a number of different collision systems and energies.Comment: Proceedings of SQM'06 Conference, LA, 2006 (submitted to J. Phys. G

Xi and AntiXi production in Pb+Pb collisions at 40 AGeV at CERN SPS

First results on the production of Xi and AntiXi hyperons in Pb+Pb interactions at 40 AGeV are presented. The AntiXi/Xi ratio at midrapidity is studied as a function of collision centrality. The ratio shows no significant centrality dependence within statistical errors; it ranges from 0.07 to 0.15. The AntiXi/Xi ratio for central Pb+Pb collisions increases strongly with the collision energy.Comment: 6 pages, 6 figures, proceedings of SQM03, to be published in Journal of Physics G; V2: changes in table 1 and figure

Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss (HBT) interferometry signatures for the particle-emitting sources of pions and kaons produced in the heavy ion collisions at GSI-FAIR energies. The evolution of the sources is described by relativistic hydrodynamics with the system equation of state of the first-order phase transition from quark-gluon plasma (QGP) to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. We find that the HBT radii of kaons are smaller than those of pions for the same initial conditions. Both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources are sensitive to the initial energy density. They are significantly prolonged when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This prolongations of the HBT lifetimes of pions and kaons may likely be observed in the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure

Omega and AntiOmega production in Pb+Pb and p+p collisions at 30, 40 and 158 AGeV

We report preliminary results on Omega and AntiOmega production in central Pb+Pb collisions at 30, 40 and 158 AGeV and p + p interactions at 158 GeV. The midrapidity AntiOmega/Omega ratio is estimated to be 0.45 +- 0.05 and 0.41 +- 0.18 for central Pb+Pb collisions at 158 and 40 AGeV, respectively. The corresponding value for 158 GeV p+p interactions is 0.67 +- 0.62. For central Pb+Pb collisions at 158 AGeV fully corrected distributions are obtained. The inverse slope parameters of the transverse mass spectrum and total yields are T(Omega) = 276 +- 23 MeV, = 0.47 +- 0.07 and T(AntiOmega) = 285 +- 39 MeV, = 0.15 +- 0.02.Comment: Contribution to the proceedings of "Strangeness in Quark Matter 2003" (March 2003, Atlantic Beach NC, USA), to be published in Journal of Physics G., 6 pages, 6 figure

Strangeness from 20 AGeV to 158 AGeV

New results from the energy scan programme of NA49, in particular kaon production at 30 AGeV and phi production at 40 and 80 AGeV are presented. The K+/pi+ ratio shows a pronounced maximum at 30 AGeV; the kaon slope parameters are constant at SPS energies. Both findings support the scenario of a phase transition at about 30 AGeV beam energy. The phi/pi ratio increases smoothly with beam energy, showing an energy dependence similar to K-/pi-. The measured particle yields can be reproduced by a hadron gas model, with chemical freeze-out parameters on a smooth curve in the T-muB plane. The transverse spectra can be understood as resulting from a rapidly expanding, locally equilibrated source. No evidence for an earlier kinetic decoupling of heavy hyperons is found.Comment: Contribution to the proceedings of "Strangeness in Quark Matter 2003" (March 2003, Atlantic Beach NC, USA), to be published in Journal of Physics G. 11 pages, 14 figure

Antideuteron and deuteron production in mid-central Pb+Pb collisions at 158AA GeV

Production of deuterons and antideuterons was studied by the NA49 experiment in the 23.5% most central Pb+Pb collisions at the top SPS energy of $\sqrt{s_{NN}}$=17.3 GeV. Invariant yields for $\bar{d}$ and $d$ were measured as a function of centrality in the center-of-mass rapidity range $-1.2<y<-0.6$. Results for $\bar{d}(d)$ together with previously published $\bar{p}(p)$ measurements are discussed in the context of the coalescence model. The coalescence parameters $B_2$ were deduced as a function of transverse momentum $p_t$ and collision centrality.Comment: 9 figure

Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy

A novel approach, the identity method, was used for particle identification and the study of fluctuations of particle yield ratios in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions ($\pi$) and electrons (e). Using these moments the excitation function of the fluctuation measure $\nu_{\text{\text{dyn}}}$[A,B] was measured, with A and B denoting different particle types. The obtained energy dependence of $\nu_{\text{dyn}}$ agrees with previously published NA49 results on the related measure $\sigma_{\text{dyn}}$. Moreover, $\nu_{\text{dyn}}$ was found to depend on the phase space coverage for [K,p] and [K,$\pi$] pairs. This feature most likely explains the reported differences between measurements of NA49 and those of STAR in central Au+Au collisions

Production of deuterium, tritium, and 3^3He in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV at the CERN SPS

Production of $d$, $t$, and $^3$He nuclei in central Pb+Pb interactions was studied at five collision energies ($\sqrt{s_{NN}}=$ 6.3, 7.6, 8.8, 12.3, and 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum spectra, rapidity distributions, and particle ratios were measured. Yields are compared to predictions of statistical models. Phase-space distributions of light nuclei are discussed and compared to those of protons in the context of a coalescence approach. The coalescence parameters $B_2$ and $B_3$, as well as coalescence radii for $d$ and $^3$He were determined as a function of transverse mass at all energies.Comment: 22 pages, 29 figures, 8 tables, for submission to Phys. Rev.

Measurement of event-by-event transverse momentum and multiplicity fluctuations using strongly intensive measures Δ[PT,N]\Delta[P_T, N] and Σ[PT,N]\Sigma[P_T, N] in nucleus-nucleus collisions at the CERN Super Proton Synchrotron

Results from the NA49 experiment at the CERN SPS are presented on event-by-event transverse momentum and multiplicity fluctuations of charged particles, produced at forward rapidities in central Pb+Pb interactions at beam momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication extends the previous NA49 measurements of the strongly intensive measure $\Phi_{p_T}$ by a study of the recently proposed strongly intensive measures of fluctuations $\Delta[P_T, N]$ and $\Sigma[P_T, N]$. In the explored kinematic region transverse momentum and multiplicity fluctuations show no significant energy dependence in the SPS energy range. However, a remarkable system size dependence is observed for both $\Delta[P_T, N]$ and $\Sigma[P_T, N]$, with the largest values measured in peripheral Pb+Pb interactions. The results are compared with NA61/SHINE measurements in $p+p$ collisions, as well as with predictions of the UrQMD and EPOS models.Comment: 12 pages, 14 figures, to be submitted to PR

Energy dependence of kaon-to-proton ratio fluctuations in central Pb+Pb collisions from sNN\sqrt{s_{NN}} = 6.3 to 17.3 GeV

Kaons and protons carry large parts of two conserved quantities, strangeness and baryon number. It is argued that their correlation and thus also fluctuations are sensitive to conditions prevailing at the anticipated parton-hadron phase boundary. Fluctuations of the $(\mathrm{K}^+ + \mathrm{K}^-)/(\mathrm{p}+\bar{\mathrm{p}})$ and $\mathrm{K}^+/\mathrm{p}$ ratios have been measured for the first time by NA49 in central Pb+Pb collisions at 5 SPS energies between $\sqrt{s_{NN}}$= 6.3 GeV and 17.3 GeV. Both ratios exhibit a change of sign in $\sigma_{\mathrm{dyn}}$, a measure of non-statistical fluctuations, around $\sqrt{s_{NN}}$ = 8 GeV. Below this energy, $\sigma_{\mathrm{dyn}}$ is positive, indicating higher fluctuation compared to a mixed event background sample, while for higher energies, $\sigma_{\mathrm{dyn}}$ is negative, indicating correlated emission of kaons and protons. The results are compared to UrQMD calculations which which give a good description at the higher SPS energies, but fail to reproduce the transition to positive values.Comment: 5 pages, 4 figure