Next-to-leading-order QCD corrections to the yields and polarisations of J/Psi and Upsilon directly produced in association with a Z boson at the LHC

TL;DR

This paper provides updated NLO QCD calculations for J/Psi and Upsilon production with Z bosons at the LHC, showing small corrections at certain P_T ranges and unchanged polarisation patterns, confirming previous assumptions.

Contribution

It presents the first detailed NLO QCD analysis of J/Psi and Upsilon production with Z bosons, including polarisation, within the Colour-Singlet Model, clarifying the impact of QCD corrections.

Findings

QCD corrections are small at small and mid P_T when scales are set to Z mass.

t-channel gluon-exchange dominates at P_T > mZ/2.

Polarisation pattern remains unchanged by QCD corrections.

Abstract

We update the study of the production of direct J/Psi in association with a Z boson at the Next-to-Leading Order (NLO) in alpha_s by evaluating both the yield differential in P_T and the J/Psi polarisation in the QCD-based Colour-Singlet Model (CSM). Contrary to an earlier claim, QCD corrections at small and mid P_T are small if one assumes that the factorisation and the renormalisation scales are commensurate with the Z boson mass. As it can be anticipated, the t-channel gluon-exchange (t-CGE) topologies start to be dominant only for P_T > mZ/2. The polarisation pattern is not altered by the QCD corrections. This is thus far the first quarkonium-production process where this is observed in the CSM. Along the same lines, our predictions for direct Upsilon+Z are also given.