Novel two-to-three hard hadronic processes and possible studies of generalized parton distributions at hadron facilities

Abstract

We consider a novel class of hard branching hadronic processes a+b->c+d+e, where hadrons c and d have large and nearly opposite transverse momenta and large invariant energy which is a finite fraction of the total invariant energy. We use color transparency logic to argue that these processes can be used to study quark generalized parton distributions (GPDs) for baryons and mesons in hadron collisions hence complementing and adding to the studies of GPDs in the exclusive DIS (deep inelastic scattering) processes. We propose that a number of GPDs can be investigated in hadron facilities such as J-PARC (Japan Proton Accelerator Research Complex) facility and GSI-FAIR (Gesellschaft fur Schwerionenforschung -Facility for Antiproton and Ion Research) project. In this work, the GPDs for the nucleon and for the N->Delta transition are studied in the reaction N+N->N+pi+B, where N, pi, and B are a nucleon, a pion, and a baryon (nucleon or Delta), respectively, with a large momentum transfer between B (or pi) and the incident nucleon. In particular, the Efremov-Radyushkin-Brodsky-Lepage (ERBL) region of the GPDs can be measured in such exclusive reactions. We estimate the cross section of the processes N+N->N+pi+B by using current models for relevant GPDs and information about large angle pi N reactions. We find that it will be feasible to measure these cross sections at the high-energy hadron facilities, and get novel information about the nucleon structure, for example, contributions of quark orbital angular momenta to the nucleon spin. The studies of N->Delta transition GPDs could be valuable also for investigating electromagnetic properties of the transition.