Probing gluon and heavy-quark nuclear PDFs with γ + Q production in pA collisions

Abstract

We present a detailed phenomenological study of direct photon production in association with a heavy-quark jet in pA collisions at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) at next-to-leading order in QCD. The dominant contribution to the cross-section comes from the gluon-heavy-quark (gQ) initiated subprocess, making γ + Q production a process very sensitive to both the gluon and the heavy-quark parton distribution functions (PDFs). Additionally, the RHIC and LHC experiments are probing complementary kinematic regions in the momentum fraction x carried by the target partons. Thus, the nuclear production ratio \( R_{pA}^{\gamma + Q} \) can provide strong constraints, over a broad x-range, on the poorly determined nuclear parton distribution functions which are extremely important for the interpretation of results in heavy-ion collisions.