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HK: Hadronen und Kerne

HK 36: Electromagnetic Probes V, CERN, HERA Results

HK 36.2: Group Report

Tuesday, March 17, 1998, 17:30–18:00, B

Target fragmentation in γ^*p and pp at high energies — •Umberto D’Alesio and H.J Pirner — Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 19, 69120 Heidelberg

Recently new data on leading neutrons in electron proton scattering have been available from the Zeus and H1 collaborations at HERA, giving a substantial fraction (∼ 10%) of DIS events.

In the meson cloud model the nucleon is seen as a bare nucleon accompanied by the mesonic cloud. Restricting to the most important π N component, the study of neutron production in DIS at HERA can then be used to extract information about the pion structure function at very small x. According to the factorization hypothesis, the virtual photon scatters on the pion and the neutron is produced as a spectator of the reaction.

A phenomenological study, in different theoretical approaches, is performed and a comparison with the process pp→ nX at ISR energies (involving the same pion exchange) is carried out. Different reggeon exchanges are also considered and the relative contributions to energy and t (momentum transfer) distributions are evaluated.
An attempt to evaluate screening corrections related to the breaking of factorization is also discussed.