Scaling in fragmentation of target spectators

The LUND string picture is a remarkably successful phenomenological description of high energy hadronization processes, occurring in jet events. The FRITIOF model is a combination of the soft collisions occurring in high energy hadron-hadron, hadron-nucleus and nucleus-nucleus collisions, followed by string fragmentation. FRITIOF and also other models for hadronic interaction which try to describe experimental observables as a superposition of nucleon-nucleon collisions describe the pseudorapidity distributions measured in emulsion experiments well, where the angular distribution of relativistic shower particles are measured. However they fail to describe the pseudorapidity distribution of charged particles at target fragmentation and midrapidity. The authors have shown that the FRITIOF model for soft hadronic processes combined with a moving thermal source for target spectator fragmentation describes the measured pseudorapidity distributions of produced hadrons at 14.5 AGeV within 10% error as well as at 60 and 200 AGeV for different targets and O16 projectiles. Their model explains why the measured baryon pseudorapidity distributions were proportional for central 60 and 200 AGeV O16+B collisions in the target fragmentation region. They are thermal distributions with T ∼ 66 MeV, moving with u ∼ 0.3c. They emphasize that the pseudorapidity distribution of the spectators given peaks at η ∼ 0.5 for b ∼ 0.6 thus the contribution of spectator fragments is not negligible for pseudorapidity η ≤ 1.5