Leadingnonleading Charm Hadroproduction in the Quark-Gluon String Model.pdf

a r X i v : h e p - p h / 9 5 0 7 2 0 3 v 1 3 J u l 1 9 9 5 Leading/nonleading Charm Hadroproduction in the Quark-Gluon String Model O.I.Piskounova Joint Institute for Nuclear Research, Dubna 141980, Russia Abstract Leading charm production in reaction π?N → DX is dis- cussed.Three experiments at Fermilab and CERN have measured a rather large enhancement in production rate of leading D?- mesons over nonleading D+.A good description of these results is obtained in Quark Gluon String Model (QGSM) if the idea of ’in- trinsic charm’ is involved. The weight of the cc? pairs in the quark sea of colliding hadrons is estimated from the experimental data. The comparison with other theoretical models is also carried out. 1 Introduction Leading effects in charm hadroproduction have been discussed [1, 2] for many years of research in this field. Measurements have been made recently in reactions like π?A → DX for the momenta of incident π??beams from 250 GeV/c to 500 GeV/c [3, 4, 5]. An essential en- chancement of leading D?- over nonleading D+-meson rates has been observed, especially in the region of Feynman’s xf →1. This asymmetry in the spectra of charmed mesons is defined everywhere as A(x) = dND ? /dx? dND+/dx dND?/dx+ dND+/dx . (1) It indicates a strong dependence on the valence quark composition of the beam particle, the so called ”beam dragging” effect. Charmed mesons, D?(dc?) and D0(u?c) in this case produced by a recombination of the u? or d valence quarks from π? with the cc? pair from fission of a string,have harder spectra than for the other D-mesons. The magnitudes of A(x) measured in WA82[3], E769[4] and E791 [5] experiments in the narrow range of √ s=23-32 GeV have close values. The models previously applied to describe the asymmetry depen- dence, were not very successful, see ref.[6], for instance. The first order QCD calculation could not produce any asymmetry because it did not 1 take into account the quark content of the beam or target particles. The mo