Nuclear Interactions of 400 GeV Protons in Emulsion

We report on 400 GeV proton-emulsion nucleus reactions and compare the results to hadron-nucleus reactions at smaller energies. In particular we present results on the emission of fast target protons (essentially grey track particles) and on their correlation with the number of collisions inside the nucleus, ν, with the number of charged evaporated particles (essentially black track particles) and with the number of pions produced (essentially shower particles). We observe that the main features of the 200¿400 GeV data are very similar. However, we find that the mean shower-particle multiplicity at 400 GeV is essentially higher than expected from the simple independent particle model prediction 〈ns〉 = 〈nch〉[1 + 0.5(〈ν〉 − 1)]. The shower particle multiplicities do not seem to follow a target mass dependence of the form 〈ns〉 = 〈nch〉 Aα with α = 0.14 or α = 0.19 as has been suggested in the literature. The pseudo-rapidity distribution shows limiting target and projectile fragmentation. The shower-particle multiplicity in the ¿central region¿ increases linearity with 〈ν〉 but faster than 0.5〈ν〉 times the corresponding multiplicity in pp reactions