Heavy Quark Correlations in Photon-Hadron Collisions

TL;DR

We address heavy-quark photoproduction in photon-hadron collisions by computing the fully exclusive cross section at next-to-leading order, i.e. at order $\mathcal{O}(\alpha_{\rm em}\alpha_{S}^2)$, and implementing it as a parton-event generator. The calculation covers the $\gamma g\to Q\bar{Q}$ two-body process and the three-body real-emission channels $\gamma g\to Q\bar{Q}g$ and $\gamma q\to Q\bar{Q}q$, using dimensional regularization in $d=4-2\epsilon$ and a subtraction scheme to cancel soft and collinear divergences. The results examine total and differential distributions for charm and bottom and assess scale and PDF uncertainties, including the hadronic (resolved) photon component. The study finds moderate NLO corrections, small hadronic-photon contributions at fixed-target energies, and generally reduced theoretical uncertainties, with non-perturbative effects potentially important for charm in some kinematic regions. The work provides a flexible tool for fixed-target and HERA phenomenology, enabling precise tests of perturbative QCD and extraction of the gluon structure function from heavy-quark photoproduction.

Abstract

We describe a next-to-leading-order calculation of the fully exclusive parton cross section for the photoproduction of heavy quarks. We use our result to compute quantities of interest for current fixed-target experiments. We discuss heavy-quark total cross sections, distributions and correlations.