KINEMATIC ENHANCEMENT OF NONPERTURBATIVE CORRECTIONS TO QUARKONIUM PRODUCTION

In this letter we address issues involved in quarkonium production nea r the boundaries of phase space, Iris shown that higher-order non-pert urbative contributions are enhanced in this kinematic region and lead to a breakdown of the nonrelativistic (NRQCD) expansion, This breakdow n is a consequence of sensitivity to the kinematics of soft gluon radi ation and to the difference between partonic and hadronic phase space. We show how these large corrections can be resummed giving the domina nt contribution to the cross section, The resummation leads to the int roduction of non-perturbative, universal distribution functions. We di scuss the importance of these shape functions for several observables, in particular the energy distribution of photo-produced J/psi close t o the endpoint. (C) 1997 Elsevier Science B.V.