Abstract

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 degrees production angle and at forward rapidity (4.3 = y = 6.3). The centrality dependence of pion production is shown in the impact parameter range similar to 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 similar to 100 and then it saturates, while at y = 6.3 it does not exhibit any sudden change as a function of Np.