The exclusive $J/\psi$ process at the LHC tamed to probe the low $x$ gluon

TL;DR

This paper demonstrates that applying a specific $Q_0$ cut to NLO calculations stabilizes perturbative predictions for exclusive $J/\psi$ production at the LHC, enabling precise probing of the low $x$ gluon distribution.

Contribution

Introducing a $Q_0$ cut in NLO calculations to improve perturbative stability in exclusive $J/\psi$ production analysis at the LHC.

Findings

Perturbative stability is significantly improved with the $Q_0$ cut.

High-precision $J/\psi$ data can determine low $x$ gluon distributions.

The method reduces sensitivity to scale choices in predictions.

Abstract

The perturbative QCD expansion for $J/\psi$ photoproduction appears to be unstable: the NLO correction is large (and of opposite sign) to the LO contribution. Moreover, the predictions are very sensitive to the choice of factorization and renormalization scales. Here we show that perturbative stability is greatly improved by imposing a $`Q_0$ cut' on the NLO coefficient functions; a cut which is required to avoid double counting. $Q_0$ is the input scale used in the parton DGLAP evolution. This result opens the possibility of high precision exclusive $J/\psi$ data in the forward direction at the LHC being able to determine the low $x$ gluon distribution at low scales.