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.     

Strangeness enhancement and strangeness suppression in nuclear collisions at 200 GeV/N

Data on yields of strange and negative hadrons in full phase space produced in proton-nucleus and central S+S collisions at 200 GeV/nucleon are reviewed. The total number of produced strange and nonstrange valence quark-antiquark pairs is determined on the basis of the hadron multiplicity at freezout. It is shown that the strangeness production factor λ _s is increased by a factor of 2 in central S+S collisions, whereas no increase is observed in proton-nucleus collisions.     

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.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p⊥<2.0 GeV/c the yield andp⊥-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p??<2.0 GeV/c the yield andp??-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Quark-gluon plasma in nuclear collisions at 200 GeV/A

Assuming complete inelasticity of nuclear collisions at 200 GeV/A we consider the properties of the arising high temperature and density nuclear matter fireball. Pion multiplicity and particle rapidity distribution can be estimated and correlated with other properties of the fireball. Consistency of the fireball reaction picture with the quark-gluon plasma structure is shown.     

Meson-baryon femtoscopy in Au+Au collisions at 200 GeV measured by STAR experiment

Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission points at freezeout [1]. Such asymmetries may arise from long-lived resonances, bulk collective effects, or differences in the freezeout scenario for the different particle species. STAR has extracted pion-proton correlation functions from a high-statistics dataset of Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. We present a femtoscopic analysis of this data for all combinations of charged pions and (anti-) protons, for collisions of different centrality. The measurements are compared with calculations of a simple Blast-wave model, in which asymmetries are driven only by collective flow, as well as with Therminator [2], which also accounts fully for resonance effects.     

Photon production in ultrarelativistic heavy-ion collisions at 200 GeV/u

A calculation of sources of inclusive photons in ultrarelativistic O-W and Pb-Pb collisions at 200 GeV/u is presented. The production of thermal photons in a quark-gluon plasma, a deconfined state of nuclear matter at high energy density, is addressed. In events with a large amount of energy deposited in the target the thermal contribution to the inclusive spectrum is found to be ～5%, quadratically increasing with particle multiplicity, but only weakly dependent on the size of the projectile nucleus. These photons are predominantly produced in a coexistence phase of plasma and hadronic matter. Hadronic bremsstrahlung is investigated including the spatial and temporal coherence due to the large space-time extension of heavy-ion systems. For small photon momenta there is a coherent signal in the fragmentation regions proportional to the squared number of participant protons.     

Study of jet fragmentation in p+p collisions at 200 GeV in the STAR experiment

The measurement of jet fragmentation functions in p+p collisions at 200 GeV is of great interest because it provides a baseline to study jet quenching in heavy-ion collisions. It is expected that jet quenching in nuclear matter modifies the jet energy and multiplicity distributions, as well as the jet hadrochemical composition. Therefore, a systematic study of the fragmentation functions for charged hadrons and identified particles is a goal both in p+p and Au+Au collisions at RHIC. Studying fragmentation functions for identified particles is interesting in p+p by itself because it provides a test of NLO calculations at RHIC energies. We present a systematic comparison of jet energy spectra and fragment distributions using different jet-finding algorithms in p+p collisions in STAR. Fragmentation functions of charged and neutral strange particles are also reported for different jet energies.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon by the CERES Collaboration

In this note we comment on a recent publication in this journal by the CERES (NA45) Collaboration [1]. The authors report to have determined an upper limit on the direct photon yield relative to the decay photon yield in S + Au collisions of 14% and 7% by two different methods, respectively. We argue that these limits are unsupported by the results and analysis of the CERES data. The systematic error estimates quoted in the CERES analysis are consistently overly optimistic. Using more realistic estimates of the various error contributions and propagating them appropriately we arrive at a direct photon upper limit which at best is 20% of the inclusive photon yield, and most probably is much higher.     

J/psi production from proton-proton collisions at square root of s=200 GeV

J/psi production has been measured in proton-proton collisions at square root of s=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mu b. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.     

Multiplicity distributions in proton-nucleus collisions at 67 and 200 GeV

New data, concerning multiplicities in collisions of 67 and 200 GeV protons in emulsions are presented. Various parameters of multiplicity distributions in collisions of protons with nuclei of photographic emulsion at primary energies between a few and about 1000 GeV are compared with p-p collisions.     

Production of charged kaons in proton-nucleus and nucleus-nucleus collisions at 200 GeV/nucleon

Production of charged kaons in proton-sulphur, proton-gold, sulphur-sulphur and oxygen-gold collisions at 200 GeV/nucleon has been studied in the NA35 Streamer Chamber experiment. Rapidity and transverse mass distributions as well as mean multiplicities were obtained. The results are compared with nucleon-nucleon data and with model predictions.Deceased     

Transverse momentum distributions of neutral pions from central and peripheral16O+Au collisions at 200A·GeV

The production of neutral pions by the interaction of 200A·GeV p and¹⁶O projectiles with a Au target has been studied in the pseudorapidity range 1.5≦η≦2.1. Transverse momentum spectra have been measured between 0.4 GeV/c and 3.6 GeV/c and their dependence on the centrality of the collision has been investigated. The peripheral-collision spectra display a marked change of slope with a hard component starting at about 1.8 GeV/c, in contrast to central-collision data. The data are discussed in comparison to p+p and α+α data from the ISR.     

Three-pion interferometry results from central Pb+Pb collisions at 158A GeV/c

Three-particle correlations have been measured for identified pi(-) from central 158A GeV Pb+Pb collisions by the WA98 experiment at CERN. A substantial contribution of the genuine three-body correlation has been found as expected for a mainly chaotic and symmetric source.     

Multiplicity distributions of produced particles in proton-nucleus collisions at 200 GeV

We analyse data for multiplicity distributions of negative particles which are produced inpp, pAr andpXe collisions, at 200 GeV. We compare two hypotheses with the data: universal (KNO) scaling and the model of independent sources. The data favour the second model.