J. Zimányi

Energy dependence of pion and kaon production in central Pb¿Pb collisions

Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.

Evidence for an Exotic S = -2, Q = -2 Baryon Resonance in Proton-Proton Collisions at the CERN SPS

Results of resonance searches in the Xi- pi-, Xi- pi+, antiXi+ pi- and antiXi+ pi+ invariant mass spectra in proton-proton collisions at sqrt{s}=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi- pi- baryon resonance with mass of 1.862+/-0.002 GeV/c^2 and width below the detector resolution of about 0.018 GeV/c^2. The significance is estimated to be 4.0 sigma. This state is a candidate for the hypothetical exotic Xi_(3/2)^-- baryon with S = -2, I = 3/2 and a quark content of (d s d s ubar). At the same mass a peak is observed in the Xi- pi+ spectrum which is a candidate for the Xi_(3/2)^0 member of this isospin quartet with a quark content of (d s u s dbar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Quark-gluon plasma formation in heavy ion collisions and quarkochemistry

Abstract Improving our quarkochemical model by an energy balance equation we point out that quark-gluon plasma formation is energetically impossible below E lab ≈ 6 GeV / nucleon bombarding energy in heavy ion collisions. We compare the predictions for the observed hadronic composition of the hadrochemical and quarkochemical model. We find that one consequence of the quark matter formation will be a decrease in the meson production, corresponding to a low temperature of the plasma, instead of the large increase expected before.

ALCOR: a dynamical model for hadronization

Abstract Hadron multiplicities are calculated in the framework of the algebraic coalescence rehadronization model (ALCOR), which counts for redistribution of quarks into hadrons for relativistic heavy-ion collisions. Dynamical in-medium suppression of the light to heavy quark coalescence factors and the influence of Bjorken flow on the final hadronic composition are incorporated in the model. A comparison is made with the CERN SPS NA35 (S+S) heavy-ion experiment where the total total quark number is fitted to the total charge multiplicity and predictions for NA49 (Pb+Pb) is presented.

Ξ− and Ξ+ production in central Pb+Pb collisions at 158 GeV/c per nucleon

Results of the production of Xi and Xi-bar hyperons in central Pb+Pb interactions at 158 GeV/c per nucleon are presented. This analysis utilises a global reconstruction procedure, which allows a measurement of 4pi integrated yields to be made for the first time. Inverse slope paramters, which are determined from an exponential fit to the transverse mass spectra, are shown. Central rapidity densities are found to be 1.49 +- 0.08 and 0.33 +- 0.04 per event per unit of rapidity for Xi and Xi-bar respectively. Yields integrated to full phase space are 4.12 +- 0.02 and 0.77 +- 0.04 for Xi and Xi-bar. The ratio of Xi-bar/Xi at mid-rapidity is 0.22 +- 0.03.

Recent results on spectra and yields from NA49

The energy dependence of hadron production in central Pb+Pb collisions is presented and discussed. In particular, midrapidity

Lambda and lambda production in central Pb-Pb collisions at 40, 80, and 158A GeV.

m_T

Quark liberation and coalescence at CERN SPS

-spectra for

Transverse momentum fluctuations in nuclear collisions at 158A GeV

\pi^-

Hadronization with a confining equation of state

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