A. Franz

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.

The mid-rapidity calorimeter for the relativistic heavy-ion experiment WA80 at CERN

Abstract A sampling calorimeter designed for use at mid-rapidity in the relativistic heavy-ion experiment WA80 at CERN is described. Calibration and performance results are presented. Over the energy range of 2 to 50 GeV, the response of the mid-rapidity calorimeter was linear, and its energy resolution σ E was found to be given by 0.014 + 0.11 √E and 0.034+0.34 √E for electromagnetic and hadronic showers, respectively. Signal ratios of 1.2 and 1.4 were obtained for the e h ratio of the lead-scintillator electromagnetic section and the iron-scintillator hadronic section, respectively. The calorimeter provided an accurate transverse energy trigger. The response and resolution for high-energy heavy ions were slightly better than anticipated on the basis of the low-energy calibrations.

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.

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.

Target fragmentation in proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon

Target remnants withZ<3 from proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon were measured in the angular range from 30° to 160° (−1.7<η<1.3) employing the Plastic Ball detector. The excitation energy of the target spectator matter in central oxygen-induced collisions is found to be high enough to allow for complete disintegration of the target nucleus into fragments withZ<3. The average longitudinal momentum transfer per proton to the target in central collisions is considerably higher in the case of16O-induced reactions (≈300 MeV/c) than in proton-induced reactions (≈130 MeV/c). The baryon rapidity distributions are roughly in agreement with one-fluid hydrodynamical calculations at 60 GeV/nucleon16O+Au but are in disagreement at 200 GeV/nucleon, indicating the higher degree of transparency at the higher bombarding energy. Both, the transverse momenta of target spectators and the entropy produced in the target fragmentation region are compared to those attained in head-on collisions of two heavy nuclei at Bevalac energies. They are found to be comparable or do even exceed the values for the participant matter at beam energies of about 1–2 GeV/nucleon.

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.

Oxygen-induced reactions at 60A GeV and 200A GeV studied by calorimetry

Results based on calorimetric measurements are presented from reactions of 60A GeV and 200A GeV16O projectiles with C, Cu, Ag, and Au nuclei. Minimum-bias cross sections are discussed. Energy spectra measured at zero degrees and transverse-energy distributions for the pseudorapidity range 2.4≦η≤5.5 are shown. An analysis of the average transverse energy in terms of the number of participating nucleons and the number of binary nucleon-nucleon collisions is presented. Estimates of nuclear stopping and of attained energy densities are made.

Bose-einstein correlations in the target fragmentation region in 200A GeV16O+nucleus collisions

Correlations between positive pions are investigated in the target fragmentation region of 200A GeV16O+nucleus collisions. The pions are measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The target mass dependence of the radii and the correlation strength extracted by interferometry is studied. A new approach to the fit of the correlation function is introduced. The correlation strength and both invariant and transverse radii increase with decreasing target mass. The transverse radius for16O+C reactions appears to be much larger than the geometrical radius of the nuclei involved. For the Au target only a small fraction of the measured pions contributes to the apparent correlation. Hints for a much larger second component in16O+Au reactions are observed. Rescattering phenomena may provide a clue to understand these phenomena.

Neutral transverse momentum spectra in 60 and 200A·GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (pT) distributions fo inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and are measured with a lead glass calorimeter in 60 and 200A·Gev16O+nucleus and and proton+nucleus reactions. Inclusive photon distributions are compared for central and peripheral reactions. The degree of centrality is determined either from the charged particle multiplicity or from the remaining projectile energy in the forward direction. Deviations from a nucleus+nucleus interaction model based upon linear extrapolation from p+p reactions are observed in central16O+Au data. The variation of theaverage transverse momentum is investigated as function of centrality. The target-mass and energy dependence of π0pT distributions are presented. For16O+Au a change of slope in these distributions is observed atpt≈0.8 GeV/c compatible with hydrodynamic expansion models.