A String Model for Hadron Interactions at High Energies

Abstract

An iterative string cascade model is extended to the SPS energies, where high order terms in the fragmentation series are considered. The derived fragmentation series converges rapidly. Terms of second and third order have significant values only at SPS energies, while the zero and the first order terms are sufficient for the hadron interactions at a few GeV. The charged particle multiplicity and the relative cross section of the production of the resonance and the prompt hadrons are reproduced with fair agreement with experimental data. 2 > It was found that the perturbative series for the total cross section converges reasonably fast. On the other hand, the problem of the multi-particle production in pp collision is dealt by different models based on soft hadronic collisions, 3 > the 1/N expansion of the amplitude for processes in QCD and string type models, describing quark transi­ tions into hadrons. At high energies there exist diagrams of complicated topology which correspond to processes with the exchange of several Pomerons. 4 > The contri­ bution of such diagrams to the scattering amplitude increases rapidly with energy more than the one Pomeron exchange contribution. The properties of iterative cascade jets with emphasis on the longitudinal degrees of freedom are studied by Field and Feynman through a dynamical picture in space-time and energy-momentum space, based upon string dynamics. In this model a scheme is considered which is symmetric with respect to particle generation from the quark and antiquark ends in a two-jet system. The particle production is considered as a tunneling process in a constant force field. Because of the three-gluon coupling, the color flux lines will not spread out over all space, as the electromagnetic field lines do, but rather be con­ strained to a thin tube like region. Within this tube, new qij pairs can be created from the available field energy. Thus the original system breaks into smaller and smaller pieces, until only ordinary hadrons remain. In the field behind the original, outgoing quark Qo a new quark pair Q1 ii1 is produced, so that the Qo may join with ih to form a hadron Qo fh, leaving the Q1 unpaired. The production of another pair qd(2 will give a hadron Q1 fh, etc. To denote this flavor ordering of the hadrons, the concept of rank is introduced. 5 >' 6 > Q;-1 q; is the ith rank hadron. From these assump­ tions one may find the resulting particle spectra in a jet. A fragmentation function