New contributions to heavy-quarkonium production

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.

Figures (12)

• Figure 1: Bound-state vertex obtained by multiplying a point vertex, representing a structureless particle, by a form factor.
• Figure 2: Box diagram.
• Figure 3: The first family (a) has 4 diagrams and the second family (b) 6 diagrams contributing the discontinuity of $gg \to \!\!\ ^3S_1 g$ at LO in QCD.
• Figure 4: Illustration of the necessity of a 4-point vertex.
• Figure 5: The gauge-invariance restoring vertex, $\Gamma^{(4)}$.