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 Δη–Δϕ 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 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 A Delta eta-Delta phi region. (C) 2011 Elsevier B.V. All rights reserved.
Measurements of direct photon production in p + Pb and p + C collisions at root(NN)-N-s = 17.4 GeV are presented. Upper limits on the direct photon yield as a function of p(T) are derived and ...compared to the results for Pb + Pb collisions at root(NN)-N-s = 17.3 GeV. The production of the eta meson, which is an important input to the direct photon signal extraction, has been determined in the eta -> 2 gamma channel for p + C collisions at root(NN)-N-s = 17.4 GeV. (c) 2012 Elsevier B.V. All rights reserved.
Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at {radical}(s{sub NN})=17.4 GeV at midrapidity (2.3 < or approx. {eta}{sub lab} < or approx. 3.0) over the range 0.7 ...< or approx. p{sub T} < or approx. 3.5 GeV/c. The spectra are compared to {pi}{sup 0} spectra measured in Pb+Pb collisions at {radical}(s{sub NN})=17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N{sub part} < or approx. 300), the yield of {pi}{sup 0}'s with p{sub T} > or approx. 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N{sub coll}), while for central Pb+Pb collisions with N{sub part} > or approx. 350, the {pi}{sup 0} yield is suppressed.
The effect of the final state Coulomb interaction on particles produced in Pb + Pb collisions at 158AGeV/c has been investigated in the WA98 experiment through the study of the pi(-)/pi(+) and K-/K+ ...ratios measured as a function of T-m- (m)0. While the ratio for kaons shows no significant T-m dependence, the pi(-)/pi(+) ratio is enhanced at small T-m - (m)0 values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the pi(-)/pi(+) ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.
Neutral pion production in central 158A GeV sup 208Pb+ sup 208 Pb collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron. The pisup 0 transverse mass spectrum has ...been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow one to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out. copyright ital 1999 ital The American Physical Society
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