Production of Heavy Quarkonium in High Energy Colliders

TL;DR

The paper addresses the dramatic mismatch between early color-singlet predictions and measured heavy quarkonium production at high energies, particularly at the Tevatron. It introduces fragmentation as the dominant mechanism at large $p_T$ and NRQCD-based color-octet factorization, unifying short-distance production with long-distance hadronization via universal NRQCD matrix elements. The authors demonstrate that color-octet fragmentation can reconcile data for prompt charmonium and bottomonium, predict polarization signatures, and provide a framework applicable to $Z^0$ decay and $B_c$ production, while outlining substantial theoretical and experimental work needed to validate the approach. The NRQCD formalism offers a comprehensive, process-spanning explanation for quarkonium production, with clear, testable predictions across colliders and decay channels.

Abstract

Recent data from the Tevatron has revealed that the production rate of prompt charmonium at large transverse momentum is orders of magnitude larger than the best theoretical predictions of a few years ago. These surprising results can be understood by taking into account two recent developments that have revolutionized the theoretical description of heavy quarkonium production. The first is the realization that fragmentation must dominate at large transverse momentum, which implies that most charmonium in this kinematic region is produced by the hadronization of individual high-$p_T$ partons. The second is the development of a factorization formalism for quarkonium production based on nonrelativistic QCD that allows the formation of charmonium from color-octet $c \bar c$ pairs to be treated systematically. This review summarizes these theoretical developments and their implications for quarkonium production in high energy colliders.