Charged hadron production in elementary and nuclear collisions at 158 GeV/c

A comparative study of p+p, p+Pb and Pb+Pb reactions is presented. For the first time, the same experimental apparatus is used for investigating the three reaction types. Data on identified baryons in the projectile hemisphere of p+p and centrality-selected p+Pb and Pb+Pb collisions are shown. Information from pion-induced interactions is used to isolate the projectile role in the observed phenomena. A common picture emerges for p+p, p+Pb and Pb+Pb reactions: with increasing centrality, the projectile baryon number is strongly "pushed" towards the backward hemisphere of the collision. Semi-inclusive data on identified pions in the forward hemisphere of p+p interactions are presented. The observed trends are compared to results on pion production in centrality-selected p+Pb and Pb+Pb reactions. It is argued that at least a part of effects observed in nuclear collisions can be explained by correlations present in p+p events. Conclusions about similarities and differences between elementary and nuclear reactions are drawn. The obtained results are followed by an inspection of the role played by resonance production in inelastic hadronic collisions. This role appears significant in many of the observed phenomena. Resonance decays influence both pion and proton production in a wide region of available phase-space. The contribution made to particle identification performance of the detector is described. It consists in a high precision calibration procedure, using radioactive 83Kr gas. This method is also applied for studying various detector effects.