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New Journal of Physics 1 (1999) 23
Charged pion production in fixed target Pb + Pb collisions at 158 GeV per nucleon
G. Ambrosini, R. Arsenescu, C. Baglin1, J. Beringer, C. Böhm, Kurt Borer, A. Bussière1, F. B. Dittus, Konrad Elsener, P. Gorodetzky, J.P. Guillaud1, P. O. Hess, S. Kabana, R. Klingenberg, T. Lindén, K. D. Lohmann, R. K. Mommsen, U. Moser, Klaus P. Pretzl, J. Schacher, B. Selldén, F. Stoffel, Jorma Tuominiemi, M. Weber, Q. P. Zhang
NA52 Collaboration(s)

Changes in pion production as a function of the impact parameter of the collision or the incident energy, may reveal characteristics of a possible first-order phase transition from nuclear to quark matter, as predicted by lattice quantum chromodynamics. In this paper we investigate charged pion production in Pb+Pb collisions at 158 GeV/nucleon near 0° production angle and at forward rapidity $(4.3\leq y \leq 6.3)$. The centrality dependence of pion production is shown in the impact parameter range ~ 2-12 fm at the rapidities y = 5.7 and 6.3. An enhancement in the pi-/pi+ ratio has been measured near beam rapidity, indicating Coulomb interaction of charged pions with the spectator protons. The charged pion yield per nucleon participating in the collision (N_p) at y = 5.7 increases faster than linearly with N_p, up to N_p~100 and then it saturates, while at y = 6.3 it does not exhibit any sudden change as a function of N_p.
1 :  LAPP - Laboratoire d'Annecy le Vieux de Physique des Particules
Physique/Physique des Hautes Energies - Expérience
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