Quarkonium momentum distributions in photoproduction and B decay

According to our present understanding many J/c production processes proceed through a colored cc̄ 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 end point 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 end point region. We then apply the model to photoproduction of J/c and J/c 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.