In order to discern coherent or collective processes from incoherent processes in nucleus-nucleus reactions at high energies, we study the transverse-momentum distribution of the produced particles with an incoherent-multiple-collision model. In this model, the projectile nucleon makes successive inelastic collisions with nucleons in the target nucleus, the probability of such collisions being given by the thickness function and the nucleon-nucleon inelastic cross section. It is assumed that each baryon-baryon collision produces particles and degrades momenta just as a baryon-baryon collision in free space, and that there are no secondary collisions between the produced particles and the nucleons. We found that the average transverse momentum and the charged-multiplicity data at Fermilab and CERN ISR energies can be well explained by such a model. However, the average transverse momentum for some events observed by the Japanese-American cooperative emulsion experiment (JACEE) associated with large energy density in the central rapidity region differ markedly from the model results. Such a deviation indicates the presence of coherent or collective effects for these collisions and may indicate the possibility of a formation of quark-gluon plasma.
It is shown that the observed dependence of multiplicity distribution on the size of the "rapidity window" and the existence of spike events are natural consequences of a previously proposed statistical model.
We have identified the first-order mixing amplitude of πNN process described by the hadron model with the second-order mixing amplitude of the same process described by the quark model. Then the expression for the coupling constant fπ of the πNN vertex with different quark wave functions and gluon propagators in different approximations has been derived. The calculation results of fπ have been compared with experimental data.
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