Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets

The multiplicity of inclusive photons has been measured on an event-by-event basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity (rho_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 1.13+-0.03 for the exponent. The mean transverse momentum, , of photons determined from the ratio of the measured electromagnetic transverse energy and photon multiplicity, remains almost constant with increasing rho_max. Results are compared with model predictions.Comment: 16 pages including 4 figure

Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions

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.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett; updated pQCD comparison due to new input from the author, updated references, corrected plotting error in figure

Directed Flow in 158 A GeV 208Pb^{208}Pb + 208Pb^{208}Pb Collisions

The directed flow of protons and positive pions have been studied in 158 A GeV Pb + Pb collisions. A directed flow analysis of the rapidity dependence of the average transverse momentum projected onto the reaction plane is presented for semi-central collisions with impact parameters of approximately 8 fm, where the flow effect is largest. The magnitude of the directed flow is found to be significantly smaller than observed at AGS energies and than RQMD model predictions.The directed flow of protons and positive pions have been studied in 158 A GeV Pb + Pb collisions. A directed flow analysis of the rapidity dependence of the average transverse momentum projected onto the reaction plane is presented for semi-central collisions with impact parameters of approximately 8 fm, where the flow effect is largest. The magnitude of the directed flow is found to be significantly smaller than observed at AGS energies and than RQMD model predictions

Source radii at target rapidity from two-proton and two-deuteron correlations in central Pb+Pb collisions at 158 A GeV

Two-proton and two-deuteron correlations have been studied in the target fragmentation region of central Pb+Pb collisions at 158 A GeV. Protons and deuterons were measured with the Plastic Ball spectrometer of the WA98 experiment at the CERN SPS. The results of one-dimensional and multi-dimensional analyses using both the Bertsch-Pratt and Yano-Koonin-Podgoretsky parameterizations of the two-particle correlation functions are presented. The proton source exhibits a volume emission, while the deuteron source, with small outward radius, appears opaque. Both proton and deuteron sources have cross-terms R_{ol}^2 and longitudinal velocities beta consistent with zero, indicating a boost-invariant expansion. The invariant radius parameter R follows an approximate A/sqrt{m} scaling while the longitudinal and transverse radii, R_{L} and R_{T}, scale approximately as A/sqrt{m_{T}} with A ~ 3 fm GeV^{1/2} in both cases

Event-by-event charged-neutral fluctuations in Pb+Pb collisions at 158 A~GeV

Charged particles and photons have been measured in central Pb+Pb collisions at 158 A GeV in a common ($\eta$ - $\phi$)-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have been analyzed %using the sliding window method in order to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged-neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the $\Delta\eta$ - $\Delta\phi$ region.Charged particles and photons have been measured in central Pb+Pb collisions at 158 A GeV in a common ($\eta$ - $\phi$)-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have been analyzed %using the sliding window method in order to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged-neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the $\Delta\eta$ - $\Delta\phi$ region.Charged particles and photons have been measured in central Pb + Pb collisions at 158 A  GeV in a common ( η – ϕ )-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have been analyzed to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged–neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the Δ η –Δ ϕ region

Collective flow and HBT in Pb+Pb collisions at the CERN-SPS

Study of elliptic emission for identified particles has been performed in 158A GeV Pb+Pb collisions near mid-rapidity region. Our preliminary results indicate the existence of the in-plane elliptic emission for pi /sup +/ and proton, and out-of-plane elliptic emission for K/sup +/ in semi-central collisions. In addition, two- pion interferometry is studied as a function of the pair direction relative to the reaction plane. (8 refs)