Hh Gutbrod

A New Component of the Collective Flow in Relativistic Heavy Ion Collisions

Abstract The reaction Au+Au at 400 MeV/nucleon is analyzed in the coordinate system given by the principal axes of the kinetic energy flow ellipsoid. In addition to the previously observed side-splash and bounce-off we find a pronounced component perpendicular to the reaction plane at mid-rapidity both in position- and momentum-space. The anisotropy is investigated as a function of multiplicity and is found to be most prominent for semi-central collisions.

Forward and transverse energy distributions in oxygen-induced reactions at 60 A GeV and 200 A GeV

Abstract Results are presented from reactions of 60 A GeV and 200 A GeV 16O projectiles with C, Cu, Ag, and Au nuclei. Energy spectra measured at zero degrees and transverse energy distributions in the pseudorapidity range from 2.4 to 5.5 are shown. The average transverse energy per participant is found to be nearly independent of target mass. Estimates of nuclear stopping and of attained energy densities are made.

Charged-particle distributions in 16O induced nuclear reactions at 60 and 200 A GeV

Abstract Results from 16 O induced nuclear interactions with C, Cu, Ag and Au targets at 60 and 200 A GeV are presented. Multiplicity and pseudorapidity-density distributions of charged particles and their dependence on the target mass number are reported. The increase in the particle density with increasing centrality, characterized by the energy flux at zero degrees, is investigated. Comparisons with the Fritiof model reveal systematic differences.

Photon and neutral pion distributions in 60 and 200 A GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (pT) distributions of inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and 200 A GeV16O+nucleus and proton+nucleus reactions. The variation of the average transverse momentum is investigated as function of centrality, determined by measurements of the remaining energy of the projectile and the charged particle multiplicity. For small values of the entropy, deduced from the multiplicity density, an increase in average pT is observed levelling off for larger values of entropy. The target-mass and energy dependence of π0 pT distributions are presented.

PRODUCTION OF SLOW SINGLY CHARGED FRAGMENTS IN 200 GEV/C HADRON NUCLEUS INTERACTIONS

Measurements of slow, singly charged fragments in the target rapidity region have been performed for proton and pion induced reactions with various nuclei at 200 GeV/c. Multiplicity, angular and energy distributions are examined and used to study the effects of rescattering in the nuclear medium. Data are compared to a “geometric cascade model” and to simulations with the VENUS 3.11 and the FRITIOF 1.7 Monte Carlo codes.

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.

Thermalization in high energy nuclear collisions

Abstract complete events of the symmetric collisions Ca + Ca at E / A = 400 MeV and 1050 MeV and Nb + Nb at E / A = 400 MeV and 650 MeV have been measured with the Plastic Ball/Wall 4π spectrometer. The degree of isotropy expressed by the ratio of the mean transverse to the mean longitudinal momentum in each event is determined as a function of the charged particle multiplicity. Also discussed are proton energy distributions at θ cm = 90° and their multiplicity dependences.

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.

Azimuthal anisotropy in S + Au reactions at 200 A GeV

Abstract Azimuthal correlations of photons produced at mid-rapidity in 200 A GeV S + Au collisions have been studied using a preshower photon multiplicity detector in the WA93 experiment. The Fourier expansion method has been employd to estimate the event plane via the anisotropy of the event as a function of centrality. The event plane correlation technique has been used to determine the true event anisotropy, beyond the anisotropy which arises due to finite multiplicity. The VENUS event generator with rescattering and proper simulation of the detector response can explain only a portion of the observed anisotropy. The residual anisotropy is found to be of the order of 5% for semi-central collisions. This suggests that directed collective flow of the produced particles is present at SPS energies.

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.