Systematics of mid-rapidity K-/pi ratio in heavy-ion collisions

It is observed that K-/pi in A+A and possibly p+p and pbar+p collisions follows an interesting systematic in omega, the pion transverse energy per unit of rapidity and transverse overlap area. The systematics show a linear increase of K-/pi with omega in the AGS and SPS energy regime and a saturation at RHIC energy. The systematics indicate that omega might be the relevant variable underlying K-/pi. At high energy, the omega variable is related to the gluon saturation scale in high density QCD, and perhaps to the initial energy density in the Bjorken picture.Comment: 4 pages, 3 figures. SQM-2001 proceeding

Hadronic centrality dependence in nuclear collisions

The kaon number density in nucleus+nucleus and p+p reactions is investigated for the first time as a function of the initial energy density $\epsilon$ and is found to exhibit a discontinuity around $\epsilon$=1.3 GeV/fm$^3$. This suggests a higher degree of chemical equilibrium for $\epsilon >$ 1.3 GeV/fm$^3$. It can also be interpreted as reflection of the same discontinuity, appearing in the chemical freeze out temperature (T) as a function of $\epsilon$. The $N^{\alpha \sim 1}$ dependence of (u,d,s) hadrons, whith N the number of participating nucleons, also indicates a high degree of chemical equilibrium and T saturation, reached at $\epsilon >$1.3 GeV/fm$^3$. Assuming that the intermediate mass region (IMR) dimuon enhancement seen by NA50 is due to open charm ($D \bar{D}$), the following observation can be made: a) Charm is not equilibrated. b) $J/\Psi/D \bar{D}$ suppression -unlike $J/\Psi/DY$- appears also in S+A collisions, above $\epsilon$ $\sim$1 GeV/fm$^3$. c) Both charm and strangeness show a discontinuity near the same $\epsilon$. d) $J/\Psi$ could be formed mainly through $c \bar{c}$ coalescence. e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a simple way to the mass gain of these particles if they are produced out of a quark gluon plasma (QGP). We discuss these results as possible evidence for the QCD phase transition occuring near $\epsilon \sim$1.3 GeV/fm$^3$.Comment: 4 pages, 4 figures, proceedings of Vth International Conference on Strangeness in Quark Matter, 20-25 July 2000, Berkeley, California. To appear in Journal of Physics G: Nuclear and Particle Physic

Centrality and sNNDependenceofthe\sqrt{s_{NN}} Dependence of the dE_{T}/d\etaand and dN_{ch}/d\eta$ in Heavy Ion Collisions at Mid-Rapidity

The PHENIX experiment at RHIC has measured transverse energy and charged particle multiplicity at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments, and experiments at lower energies. The $\sqrt{s_{NN}}$ dependence of $dE_{T}/d\eta$ and $dN_{ch}/d\eta$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE_{T}/d\eta$ and $dN_{ch}/d\eta$ is similar at all measured incident energies. At RHIC energies the ratio of transverse energy per charged particle was found independent of centrality and growing slowly with $\sqrt{s_{NN}}$. A survey of comparisons between the data and available theoretical models is also presented.Comment: Proccedings of the Workshop: Focus on Multiplcity at Bari, Italy, June 17-19,2004. To be submitted to the Jornal of Physics, "Conference series". Includes: 20 Pages, 15 figures, 3 Tables, 80 Referencie

Does HBT Measure the Freeze-out Source Distribution?

It is generally assumed that as a result of multiple scattering, the source distribution measured in HBT interferometry corresponds to a chaotic source at freeze-out. This assumption is subject to question as effects of multiple scattering in HBT measurements must be investigated within a quantum-mechanical framework. Applying the Glauber multiple scattering theory at high energies and the optical model at lower energies, we find that multiple scattering leads to an effective HBT density distribution that depends on the initial chaotic source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004, Oakland, California, USA, to be published in the Proceeding

On the exact conservation laws in thermal models and the analysis of AGS and SIS experimental results

The production of hadrons in relativistic heavy ion collisions is studied using a statistical ensemble with thermal and chemical equilibrium. Special attention is given to exact conservation laws, i.e. certain charges are treated canonically instead of using the usual grand canonical approach. For small systems, the exact conservation of baryon number, strangeness and electric charge is to be taken into account. We have derived compact, analytical expressions for particle abundances in such ensemble. As an application, the change in $K/\pi$ ratios in AGS experiments with different interaction system sizes is well reproduced. The canonical treatment of three charges becomes impractical very quickly with increasing system size. Thus, we draw our attention to exact conservation of strangeness, and treat baryon number and electric charge grand canonically. We present expressions for particle abundances in such ensemble as well, and apply them to reproduce the large variety of particle ratios in GSI SIS 2 A GeV Ni-Ni experiments. At the energies considered here, the exact strangeness conservation fully accounts for strange particle suppression, and no extra chemical factor is needed.Comment: Talk given at Strangeness in Quark Matter '98, Padova, Italy (1998). Submitted to J.Phys. G. 5 pages, 2 figure

Energy dependence of kaon production in central Pb+Pb collisions

Recent results from the NA49 experiment on the energy dependence of charged kaon production in central Pb+Pb collisions are presented. First results from the new data at 80 AGeV beam energy are compared with those from lower and higher energies. A difference in the energy dependence of the / and / ratios is observed. The / ratio shows a non-monotonic behaviour with a maximum near 40 AGeV.Comment: 8 pages, 7 figures, proceedings of talk at SQM2001, Frankfurt, Germany, to appear in J. Phys.

Systematics of mid-rapidity E{sub T} and multiplicity distributions in nucleus and nucleon collisions at AGS energies

In the period 1986--1992, the E802 Collaboration at the BNL-AGS made systematic measurements of transverse energy (E{sub T}) emission in an electromagnetic calorimeter (PbGl) which covered the pseudorapidity interval 1.25 {le} {eta} {le} 2.50 and half the azimuth (where mid-rapidity for these energies is y{sub cm}{sup N N} {approx_equal} 1.6 - 1.7 depending the species). The other half of the azimuth was occupied by a 25 msr magnetic spectrometer with full particle identification. Runs were also taken with two different full-azimuth configurations of the PbGl, covering 1.25 {le} {eta} {le} 2.44, and also 1.3 {le} {eta} {le} 2.4. It was noticed that the shapes of the upper edges of the E{sub T} distributions, as represented for example by the p parameter in a gamma distribution fit, seemed to vary with the solid angle of the configuration. To systematically investigate this effect, the A-dependence and pseudorapidity-interval ({delta}{eta}) dependence of E{sub T} distributions in the half-azimuth electromagnetic calorimeter were measured for p+Be, p+Au, O+Cu, Si+Au and Au+Au collisions

Two particle correlations at mid-rapidity in Si+A and Au+Au from E859/E866

Two particle correlation measurements for {ital Si-A} and {ital Au- Au} collisions from Brookhaven E859 and E866 are discussed. These measurements allow us, with some interpretation, to deduce the size of the participant region in a heavy ion collision. We show that various source parameterizations yield consistent results and we explore the dependence of the apparent source size on the pion yield