TTP99-55 Quarkonium momentum distributions in photoproduction and B decays

According to our present understanding many J/Psi production processes proceed through a coloured c\bar{c} state followed by the emission of soft particles in the quarkonium rest frame. The kinematic effect of soft particle emission is usually a higher-order effect in the non-relativistic expansion, but becomes important near the kinematic endpoint of quarkonium energy (momentum) distributions. In an intermediate region a systematic resummation of the non-relativistic expansion leads to the introduction of so-called shape functions'. In this paper we provide an implementation of the kinematic effect of soft gluon emission which is consistent with the non-relativistic shape function formalism in the region where it is applicable and which models the extreme endpoint region. We then apply the model to photoproduction of J/Psi and J/Psi production in B meson decay. A satisfactory description of B decay data is obtained. For inelastic charmonium photoproduction we conclude that a sensible comparison of theory with data requires a transverse momentum cut larger than the currently used 1 GeV.