Testing the QCD fragmentation mechanism on heavy quarkonium production at LHC

TL;DR

This paper calculates the NLO fragmentation function for charm quarks into J/psi, predicts measurable transverse momentum distributions at the LHC, and proposes testing the QCD fragmentation mechanism in heavy quarkonium production.

Contribution

It provides the first NLO calculation of the charm to J/psi fragmentation function and predicts observable effects at the LHC to test QCD fragmentation mechanisms.

Findings

NLO fragmentation function shows larger momentum fraction for J/psi.

Transverse momentum distribution is enhanced by a factor of 2.0–3.3 at NLO.

Predictions are feasible for measurement at the LHC with charm tagging.

Abstract

We calculate the fragmentation function for charm quark into J/psi at the QCD next-to-leading-order (NLO) and find that the produced J/psi is of larger momentum fraction than it is at the leading-order. Based on the fragmentation function and partonic processes calculated at the NLO, the transverse momentum distribution on J/psi hadroproduction associated with a charm c (or \bar{c}) jet are predicted. We find that the distribution is enhanced by a factor of 2.0--3.3 at the NLO as p_t increased from 10 GeV to 100 GeV and it is measurable at the LHC with charm tagger. The measurement at the LHC will supply a first chance to directly test the QCD fragmentation mechanism on heavy quarkonium production where the fragmentation function is calculable in perturbative QCD. It is also applied to J/psi (Upsilon) production in the decay of Z^0 (top quark).