Beyond The Colour-Singlet Model For Inelastic J/\psi Photoproduction

Abstract

Bound-state corrections to $J/\psi$ production from almost real photons are calculated in the colour-singlet model. A systematic, gauge-invariant, theory of hard quarkonium processes is used upto $O(v^2)$, where $v$ is the relative velocity of the quarks. The internal structure of the meson is characterised by two parameters, $\epsilon_B/M$ and $\nabla^2 \phi(0)/M^2 \phi(0)$, in addition to the usual wavefunction at the origin $\phi(0)$. These parameters are constrained to be consistent with measured leptonic decay of the $J/\psi$ and hadronic and radiative decays of $\eta_c$.