Color-octet quarkonia production

Gluon fragmentation represents the dominant source of high energy prompt quarkonia at hadron colliders. Fragmentation approximations break down, however, when a quarkonium's tranvserse momentum becomes comparable to its mass. In this paper we identify a large class of color-octet diagrams that mediate quarkonia production at all energies and reduce to the dominant set of gluon fragmentation graphs in the high ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$ limit. They contribute to quarkonia differential cross sections at the same order as color-singlet diagrams and bring theoretical predictions for \ensuremath{\Upsilon} and \ensuremath{\Psi} production at the Fermilab Tevatron into agreement with experimental measurements. Using recent CDF data we extract numerical values for bottomonia and charmonia color-octet matrix elements which are consistent with NRQCD scaling rules. We also find that quarkonia generated via the color-octet mechanism are strongly polarized at low as well as high energies. Spin alignment measurements can thus test the color-octet quarkonia production picture. \textcopyright{} 1995 The American Physical Society.

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