Kinematic enhancement of non-perturbative corrections to quarkonium production

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