Probing nuclear parton densities (and more) from γ plus Q production in p-A and A-A collisions

We present a detailed phenomenological study of the associated production of a prompt photon and a heavy-quark jet (charm or bottom) in proton-nucleus (p-A) collisions. The dominant contribution to the cross-section comes from the gluon-heavy-quark (gQ) initiated subprocess, making this process very sensitive to the gluon and the heavy quark nuclear parton densities. We show that the future p-A data to be collected at the LHC in this channel should help to disentangle the various nPDF sets currently available. In heavy-ion collisions, the photon transverse momentum can be used to gauge the initial energy of the massive parton propagating through the dense QCD medium produced in those collisions, making gamma + Q production a powerful process in order to probe energy loss dynamics in the heavy-quark sector.