R. Bock

A highly-segmented ΔE-time-of-flight wall as forward detector of the 4π-system for charged particles at the SIS/ESR accelerator

Abstract At the SIS/ESR accelerator facility at GSI in Darmstadt the 4π-detector system FOPI is under construction at present. It is designed for the investigation of central collisions of heavy ions in the energy range up to 2 A GeV. As phase I of this detector a forward wall has been built and used in various experiments. It comprizes a total number of 764 scintillators with an additional shell of 188 thin ΔE -detectors in front of it and covers the full azimuth of the polar angles from 1° to 30°. The velocity and the nuclear charge of the fragments are determined by a combined time-of-flight and ΔE measurement.

Production of η mesons in 200 AGeV/cS+S and S+Au reactions

Abstract Minimum Bias production cross sections of η mesons have been measured in 200 AGeV/cS+Au and S+S collisions at the CERN SPS by reconstructing the η → γγ decay. The measurements have been made over the rapidity range 2.1 ≤ y ≤ 2.9 using the leadglass spectrometer of WA80. Within the statistical and systematical uncertainties the spectral shapes of π0 and η mesons yields are identical when their invariant differential cross section is plotted as a function of the transverse mass. The relative normalization of the η to π0 transverse mass spectra is found to be 0.53±0.07 for S+Au and 0.43±0.15 for S+S reactions. Extrapolation to full phase space leads to an integrated cross section ratio of η to π0 mesons of 0.147±0.017(stat.)±0.015(syst.), and 0.120±0.034(stat.)±0.022(syst.) for S+Au and S+S collisions, respectively.

Systematics of inclusive photon production in 158-A-GeV Pb induced reactions on Ni, Nb, and Pb targets

The multiplicity of inclusive photons has been measured on an event-by-event basis for 158PA GeV Pb induced reactions Ž . on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity r and the width of the max pseudorapidity distributions have been studied for varying centralities for these collisions. A power law fit to the photon yield as a function of the number of participating nucleons gives a value of 1.120.03 for the exponent. The mean 2 : transverse momentum, p , of photons determined from the ratio of the measured electromagnetic transverse energy and T photon multiplicity, remains almost constant with increasing r . Results are compared with model predictions. q 1999 max Published by Elsevier Science B.V. All rights reserved.Abstract The multiplicity of inclusive photons has been measured on an event-by-event basis for 158· A GeV Pb induced reactions on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity ( ρ max ) and the width of the pseudorapidity distributions have been studied for varying centralities for these collisions. A power law fit to the photon yield as a function of the number of participating nucleons gives a value of 1.12±0.03 for the exponent. The mean transverse momentum, 〈 p T 〉, of photons determined from the ratio of the measured electromagnetic transverse energy and photon multiplicity, remains almost constant with increasing ρ max . Results are compared with model predictions.

Elliptic emission of K+ and π+ in 158 A·GeV Pb + Pb collisions

An event-by-event analysis of the azimuthal angular correlation with respect to the reaction plane has been carried out for K+ and pi(+) emission near mid-rapidity in 158 A . GeV Pb + Pb collisions. In semi-central collisions, K+ mesons are found to be preferentially emitted out of the reaction plane, while pi(+) mesons are emitted in the reaction plane. The results suggest that the kaon emission is influenced by in-medium potential effects in addition to collective flow effects

Intermittency in 32S+S and 32S+Au collisions at the CERN SPS

Abstract Nonstatistical or “intermittent” fluctuations of charged particle multiplicities have been investigated at the CERN SPS with the WA80 multiplicity array for 32S+S and 32S+Au collisions of varying centrality. Within the phase space domain studied there is no evidence for intermittency in these collisions beyond that accounted for by FRITIOF filtered through a full detector simulation.

Recent results from the WA80 experiment at CERN

Abstract Results from the WA80 experiment on systematics of global observables, dE T / dη and dN ch / dη , as well as on spectra of identified particles are presented. Special attention is given to the target fragmentation region where two-pion correlations and proton distributions have been measured. Incorporation of strong rescattering phenomena into string models is found to provide a good description of most experimental data. Deviations to this are pointed out. The present status of the γ thermal / π 0 ratio as a signal of the quark gluon plasma is discussed.

COMPARISON OF PI(0) AND ETA-SPECTRA FROM S + AU COLLISIONS AT 200 GEV/C

Neutral pi0 and eta spectra have been obtained over a wide transverse momentum range for various centralities of S + Au collisions at 200 GeV/nucleon. The analysis was done of the full statistics of the WA80 experiment at CERN using the two-photon invariant mass spectra. Compared to the previous analysis [1, 2] the pi0 and eta spectra were obntained over an extended p(t) range of 0.2 <p(t)(pi0) <4.4 GeV/c and 0.4 <p(t)(eta) <3.0 GeV/c.

Photon and neutral meson data from the collision of 200 A · GeV sulphur ions with gold targets

Using a 3790 module lead glass photon spectrometer π° and η mesons have been measured in 200 A · GeV S + Au collisions by invariant mass reconstruction. Centrality selected transverse momentum π° spectra have been obtained for 0.5 ≤ pT ≤ 4.0 GeV/c displaying a much flatter slope for central compared to peripheral data. The problems of extracting single photon to π° yields from the data are discussed and the total error of their determination is given for present and future experiments. It is concluded that an accuracy of about 7 % can be obtained in the γπ° ratio.