S. Saini

MULTIPLICITY AND PSEUDORAPIDITY DISTRIBUTIONS OF CHARGED-PARTICLES FROM S-32 INDUCED HEAVY-ION INTERACTIONS AT 200-A GEV

Multiplicity and pseudorapidity distributions have been measured for32S+Al, Cu, Ag and Au at 200A GeV. The widths of the pseudorapidity distributions increase from central to peripheral collisions. The main contribution is assumed to come from the increasing fraction of charged particles stemming from the fragmentation of the target for peripheral collisions as compared to central collisions. On the average 170–180 charged particles per unit of pseudorapidity are attained for the most central32S+Au events at the maximum of the distribution. The target dependence of the yield of charged particles for central collisions is investigated. In the target rapidity region the yield is directly proportional to the target mass. The transverse energy per charged particle has been studied as a function of centrality and pseudorapidity. The experimental results are compared to the results from the Monte-Carlo model VENUS 3.11 which includes rescattering among secondaries. A comparison between different centrality triggers is made.

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and16O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and π0 spectra have been measured in the pseudorapidity range 1.5≦η≦2.1 for the transverse momentum region 0.4 GeV/c≦pT≦2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of π0 and η mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.

Fluctuations and intermittency in 200 A GeV 16O+(C, Au) reactions

Abstract Fluctuations in the pseudo-rapidity density of charged particles in 16 O+(C, Au) reactions at 200 A GeV were analyzed with the method of scaled factorial moments. The extracted moments are proportional to a power of the pseudo-rapidity bin size, which is consistent with intermittent behaviour. The dependence on target and on impact parameter are studied. The fluctuations are stronger for systems with fewer participating nucleons.

PION ABSORPTION IN EXCITED NUCLEAR-MATTER

The target dependence and azimuthal correlations of protons and pions are investigated for pA reactions at 4.9, 60 and 200 GeV. The experimental observations can be understood qualitatively under the assumption that pions are absorbed in excited target spectator matter.

Transverse energy production in the target fragmentation region in16O-nucleus reactions at 60 and 200A GeV

Charged pion yields and transverse energies of baryons are measured for the reaction16O+Cu, Ag, Au at 60 and 200A GeV bombarding energy in the target fragmentation region employing the Plastic Ball detector. Only little dependence of the measured quantities on the bombarding energy is found. The data are compared with the multi-chain fragmentation model of Ranft. As a result it turns out that a leading order formation zone cascade is not sufficient to explain the baryon yield and the transverse energies of baryons in the target fragmentation region.

Global and local fluctuations in multiplicity and transverse energy for central ultra-relativistic heavy-ion interactions

We present results from a comparison between experimental data and model calculations, in this case represented by the Fritiof model, regarding global and local fluctuations in the distributions of transverse energy and charged particle multiplicity. The results indicate that the observed fluctuations originate predominantly from the distribution of emitting sources, i.e. either the number of participating nucleons or the number of binary collisions. The apparently larger widths of the distributions observed in restricted regions of phase space, are explained to be of purely statistical nature. As a result of the analysis the cross section for events with energy densities much larger than the typical value for a central collision is limited. The very small scales, normally associated with studies of intermittent behaviour, are not within the scope of this paper. The results of the analysis are essentially independent of whether intermittence is of importance in the reactions or not.

Results from WA80 on transverse energy production, fluctuations in multiparticle production, and γ/π0 ratios

Abstract Results are presented concerning transverse energy production from the WA80 run of 1987 using beams of E/A = 200 GeV 32 S produced by the CERN SPS. Comparisons are made to the earlier results obtained with E / A = 60 and 200 GeV 16 0. The results of an analysis of fluctuations in the charged-particle pseudorapidity densities for the 16 0 data are presented next. These analyses were carried out following a method suggested by Bialas and Peschanski. This reveals fluctuations down to pseudorapidity scales of δ = 0.1. Finally, a preliminary value is presented for the excess of observed photons over known sources in reactions of E/A = 200 GeV 16 O + Au . These measurements span the pseudorapidity interval 1.5 T = 0.4–2.4GeV/c. This excess is observed for central O + Au collisions but not for peripheral O + Au collisions.

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.

INTERMITTENCY IN 200 GEV/NUCLEON S+S COLLISIONS

We have studied one and two-dimensional intermittency in S+S collisions at 200 GeV/nucleon in a high statistics electronic measurement at the CERN SPS using pad-readout streamer tubes. We observe no intermittency signal beyond that produced by folding the Fritiof event generator with a detailed model of our detector. Even though the observed signal contains significant distortions due to experimental effects, we show that we are sensitive to intermittency in the collision.