Threshold resummation in direct photon production and its implications on the large-x gluon PDF

Abstract

Currently, the gluon distribution function is mainly constrained by jet data. Yet, its high-x behaviour is largely unknown. This kinematic region is important, for instance, for the understanding of the production of a massive state at forward rapidities at the LHC. In the past, single inclusive direct photon data from fixed target experiments was used to constrain the gluon distribution due to its dominant contribution from the $qg \rightarrow\gamma q$ subprocess in proton-proton collisions. Due to disagreement with its theoretical predictions at next-to-leading order (NLO) in perturbative QCD (pQCD), direct photon data have been excluded from global fits. This talk will discuss an improvement to such theoretical predictions by including \emph{threshold resummation} at next-to-leading logarithmic accuracy (NLL) and its impact on gluon distribution at large-x using Bayesian reweighting technique.