Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions

A new Coulomb correction method for Bose-Einstein correlations, based on the Pi+ Pi- correlation measurements

We present the measured correlation functions for pi+ pi-, pi- pi- and pi+ pi+ pairs in central S+Ag collisions at 200 GeV per nucleon. The Gamov function, which has been traditionally used to correct the correlation functions of charged pions for the Coulomb interaction, is found to be inconsistent with all measured correlation functions. Certain problems which have been dominating the systematic uncertainty of the correlation analysis are related to this inconsistency. It is demonstrated that a new Coulomb correction method, based exclusively on the measured correlation function for pi+ pi- pairs, may solve the problem

Strangeness Enhancement in Sulphur-Nucleus Collisions at 200 GeV/N

The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35 K$^0_S$ in S+S and S+Ag are consistent with the NA44 results for K$^+$ and K$^-$. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of $\Lambda$ to $\overline{\Lambda}$ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to $\pi^-$ is observed in S+Ag collisions compared to p+S reactions at the same energy. The K$^0_S$ multiplicity in full phase space per negative hadron (h$^-$) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for the K$^0_S$ multiplicity per h$^-$ in S+Pb is below the N+N value.Comment: 13 pages, 8 Figure

The strange-quark chemical potential as an experimentally accessible "order parameter" of the deconfinement phase transition for finite baryon-density

We consider the change of the strange-quark chemical potential in the phase diagram of nuclear matter, employing the Wilson loop and scalar quark condensate order parameters, mass-scaled partition functions and enforcing flavor conservation. Assuming the region beyond the hadronic phase to be described by massive, correlated and interacting quarks, in the spirit of lattice and effective QCD calculations, we find the strange-quark chemical potential to change sign: from positive in the hadronic phase - to zero upon deconfinement - to negative in the partonic domain. We propose this change in the sign of the strange-quark chemical potential to be an experimentally accessible order parameter and a unique, concise and well-defined indication of the quark-deconfinement phase transition in nuclear matter.Comment: 22 pages, 14 figures within text, 2 figures(6,B3) as separate files. To be published in J.Phys.G: Nucl.&Part.Phys. G28 (2002

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

Strangeness and Quark Gluon Plasma

A brief summary of strangeness mile stones is followed by a chemical non-equilibrium statistical hadronization analysis of strangeness results at SPS and RHIC. Strange particle production in AA interactions at \sqrt{s_{NN}}\ge 8.6 GeV can be understood consistently as originating from the deconfined quark--gluon plasma in a sudden hadronization process. Onset of QGP formation as function of energy is placed in the beam energy interval 10--30A GeV/c. Strangeness anomalies at LHC are described.Comment: 30 pages including numerouse figures, tables. Opening Lecture: Strangeness and Quark Gluon Plasma -- what has been learned so far and where do we go at SQM2003, North Carolina, March 2003, submitted to J. Phys.

Multi-Pion Correlation Effects on Two-Pion Interferometry

A general derivation of the multi-pion correlation function for completely chaotic source is given. Its effects on the pion multiplicity distribution, two-pion interferometry are studied. A generalized multi-pion correlation function for a partially coherent source is also discussed.Comment: 17 pages, six figures available upon requeste

Finite coherent length and multi-pion correlation effects on two-pion interferometry

The effects of multi-pion correlations and finite coherent length on two-pion interferometry are studied. It was shown that as the pion multiplicity and coherent length become larger, the apparent radius and the apparent coherent parameters derived from two-pion interferometry become smaller. The influence of the coherent length on the effective temperature is discussed.Comment: 5 pages, two figure

Mapping out the QCD phase transition in multiparticle production

We analyze multiparticle production in a thermal framework for 7 central nucleus nucleus collisions, $e^+$+ $e^-$ annihilation into hadrons on the Z resonance and 4 hadronic reactions (p+p and p+$\bar{p}$ with partial centrality selec tion), with center of mass energies ranging from $\sqrt{s}$= 2.6 GeV (per nucleon pair) to 1.8 TeV. Thermodynamic parameters at chemical freeze-out (temperature and baryon and strangeness fugacities) are obtained from appropriate fits, generally improving in quality for reactions subjected to centrality cuts. All systems with nonvanishing fugacities are extrapolated along trajectories of equal energy density, density and entropy density to zero fugacities. The so obtained temperatures extrapolated to zero fugacities as a function of initial energy density $\epsilon_{in}$ universally show a strong rise followed by a saturating limit of $T_{lim}$ = 155 $\pm$ 6 $\pm$ 20 MeV. We interpret this behaviour as mapping out the boundary between quark gluon plasma and hadronic phases. The ratio of strange antiquarks to light ones as a function of the initial energy density $\epsilon_{in}$ shows the same behaviour as the temperature, saturating at a value of 0.365 $\pm$ 0.033 $\pm$ 0.07. No distinctive feature of 'strangeness enhancement' is seen for heavy ion collisions relative to hadronic and leptonic reactions, when compared at the same initial energy density