Issues in Quarkonium Production

TL;DR

This paper reviews the application of Non-Relativistic QCD (NRQCD) to quarkonium production, discussing its successes, challenges, and potential for future experimental tests, especially at the Tevatron.

Contribution

It highlights the implications of NRQCD's colour-octet mechanism for charmonium production and discusses the theory's testing prospects through various experimental measurements.

Findings

NRQCD successfully explains some quarkonium production data

Discrepancies exist between NRQCD predictions and HERA photoproduction results

Future tests at Tevatron could validate or challenge NRQCD predictions

Abstract

In this talk, I start with a brief introduction to Non-Relativistic QCD (NRQCD) and its applications to quarkonium physics. This theory has provided a consistent framework for the physics of quarkonia, in particular, the colour-octet Fock components predicted by NRQCD have important implications for the phenomenology of charmonium production in experiments. The applications of NRQCD to $J/\psi$ production at Tevatron and the tests of the theory in other experiments is discussed. In particular, the apparent disagreement of NRQCD with results from HERA on inelastic photoproduction of $J/\psi$ is discussed and it is shown that the results are rather susceptible to intrinsic transverse momentum smearing. The photoproduction data, therefore, do not provide a good test of NRQCD. It is argued that NRQCD may be tested stringently by looking for the production of other charmonium resonances at the Tevatron, because the production rates for these resonances can be predicted within the NRQCD framework.