H. Ströbele

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.

MEDIUM EFFECTS IN KAON AND ANTIKAON PRODUCTION IN NUCLEAR COLLISIONS AT SUBTHRESHOLD BEAM ENERGIES

Production cross sections of

Neutral strange particle production in sulphur-sulphur and proton-sulphur collisions at 200 GeV/nucleon

{K}^{+}

The kaon spectrometer at SIS

and

Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

{K}^{\ensuremath{-}}

Enhanced out-of-plane emission of K+ mesons observed in Au + Au collisions at 1-A/GeV

mesons have been measured in

Recent results from the NA35 collaboration at CERN

\mathrm{C}+\mathrm{C}

Partial wave analysis of the reaction p(3.5 GeV)+p → pK+Λ to search for the “ppK−” bound state

collisions at beam energies per nucleon below and near the nucleon-nucleon threshold. At a given beam energy, the spectral slopes of the

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

{K}^{\ensuremath{-}}