M. Kurata

Centrality Dependence of Neutral Pion Production in 158A GeV

The production of neutral pions in 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied for the range 0.3 GeV/c<mT-m0<4.0 GeV/c. The results for central collisions are compared to various models. The centrality dependence of the neutral pion spectral shape and yield is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with greater than about 30 participating nucleons which is most naturally explained by assuming an equilibrated system.

^{208}

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.

Pb+

Abstract We have studied the timing and light yield characteristics of long and thin scintillator samples of various sizes. Both the light yield and the time resolution degrade exponentially with respect to the distance from one end; the inverse slope parameters for the time resolutions are found to be twice those of the light yield. This is interpreted in terms of a photoelectron statistics picture, which can also explain the observed position dependence of time resolution for time-of-flight counters.

^{208}

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

Pb Collisions

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in Pb-208 + Pb-208 collisions at 158 (.) A GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.Abstract.The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in 208Pb + 208Pb collisions at 158

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

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Study of timing degradation and light attenuation in long plastic scintillation rods for time-of-flight counters in relativistic heavy ion experiments

GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.

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

A large acceptance tracking system, specially developed for tracking at very high particle densities encountered in ultra-relativistic heavy-ion collisions is described. The system is a combination of multi-step avalanche chambers equipped with electronic pad readout with high position resolution in two dimensions and streamer-tube detectors with pad readout, with coarser position resolution, that is sufficient for safe pattern recognition. A high-resolution time-of-flight system (time resolution better than 90 ps) provides particle identification up to 8 GeV/c for pions and protons and pion/kaon separation up to 4 GeV/c. All detectors in the tracking system are read out with new, high-performance integrated circuits. The system can operate at high event rates due to efficient zero suppression. The performance of the system for tracking under real running conditions with Pb-beam at 158 A GeV in the WA98 experiment at CERN is presented

Azimuthal anisotropy of photon and charged particle emission in Pb-208+Pb-208 collisions at 158 center dot A GeV/c

Abstract We constructed gas a Cherenkov beam counter for a lead beam to obtain start signals of time of fight measurements for relativistic heavy ion experiments in WA98 at CERN-SPS. The intrinsic timing resolution of the gas Cherenkov counter was found to be ≤ 30 ps at a beam intensity up to 3 × 10 5 ions/s and the charge resolution ( ΔZ Z ) was 2.0% for lead ions of 160 GeV/ c per nucleon. This counter has been successfully operated for more than 1 1 2 month of heavy ion run in 1995.

A large-acceptance spectrometer for tracking in a high-multiplicity environment, based on space point measurements and high-resolution time-of-flight

The Delta(++)-resonance production in central 158 A GeV Pb-208 + Pb-208 collisions at the CERN SPS has been studied. The Delta(++) production was estimated from the invariant mass spectrum of p pi(+)-pairs by subtracting a mixed event background. The measured Delta(++) abundance is compared with the results from other experiments at lower energies, and with a model calculation assuming thermal and chemical equilibrium