Heavy Quarkonium Production: Extending CSM and COM

Abstract

By questioning the applicability of the static approximation of the Colour-Singlet Model, we have seen that the production amplitude receives contributions from two different cuts. The first one in its static limit gives the colour-singlet mechanism. The second one has not been considered so far. We treat it in a gauge-invariant manner by introducing necessary new 4-point vertices, suggestive of the colour-octet mechanism. This new contribution can be as large as the colour-singlet mechanism at high pT, however these vertices are not totally constrained and when the freedom in their determination is fully exploited, we are able to reproduce the production cross-sections at the Tevatron for the J/Psi, Psi' and Upsilon(1S) and at RHIC for the J/Psi.