engleski

Prompt photon-jet angular correlations at central rapidities in p+A collisions

Photon-jet azimuthal correlations in proton- nucleus collisions are a promising tool for gaining information on the gluon distribution of the nucleus in the regime of nonlinear color fields. We compute such correlations from the process g-> q qbar gamma in the rapidity regime where both the projectile and target light-cone momentum fractions are small. By integrating over the phase space of the quark which emits the photon, subject to the restriction that the photon picks up most of the transverse momentum (to pass an isolation cut), we effectively obtain a g+A -> q gamma process. For nearly back-to-back photon-jet configurations we find that it dominates over the leading-order process q + A -> q gamma by two less powers of Q_perp/Q_S, where Q_perp and Q_S denote the net photon-jet pair momentum and the saturation scale of the nucleus, respectively. We determine the transverse- momentum-dependent gluon distributions involved in g+A -> q gamma and the scale where they are evaluated. Finally, we provide analytic expressions for <cos n*phi> moments, where phi is the angle between Q_perp and the average photon- jet transverse momentum tilde^P_perp, and first qualitative estimates of their transverse momentum dependence.

Quantum Chromodynamics, quark and gluon jets, photon

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