New contributions to heavy-quarkonium production
arXiv:hep-ph/0507060 · doi:10.1016/j.physletb.2005.11.073
Abstract
We reconsider quarkonium production in a field-theoretical setting and we show that the lowest-order mechanism for heavy-quarkonium production receives in general contributions from two different cuts. The first one corresponds to the usual colour-singlet mechanism. The second one has not been considered so far. We treat it in a gauge-invariant manner, and introduce new 4-point vertices, suggestive of the colour-octet mechanism. These new objects enable us to go beyond the static approximation. We show that the contribution of the new cut can be as large as the usual colour-singlet mechanism at high transverse momentum for J/psi. In the psi' case, theoretical uncertainties are shown to be large and agreement with data is possible.
16 pages, 12 figures, LaTeX. References updated, typo fixed, discussion of the scale dependence, minor corrections to the text