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

Abstract

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 non-linear color fields. We compute such correlations from the process $g+A\to q\bar{q}\gamma$ 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 $g+A\to q\gamma$ process. For nearly back-to-back photon-jet configurations we find that it dominates over the leading order process $q+A\to q\gamma$ by two less powers of $Q_{\perp }/Q_S$, where ${\mathbf{Q}}_{\perp }$ 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 $g+A\to q\gamma$ and the scale where they are evaluated. Finally, we provide analytic expressions for $⟨\cos n\varphi ⟩$ moments, where $\varphi$ is the angle between ${\mathbf{Q}}_{\perp }$ and the average photon-jet transverse momentum ${\tilde{\mathbf{P}}}_{\perp }$, and first qualitative estimates of their transverse momentum dependence.

arXiv commentv3: more elaborated discussions on photon isolation cut, a few new references, results unchanged, accepted for publication in PRD

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• Isolated photon-hadron production in high energy $pp$ and $pA$ collisions at RHIC and LHC
• Inclusive prompt photon-jet correlations as a probe of gluon saturation in electron-nucleus scattering at small $x$
• Harmonics of Parton Saturation in Lepton-Jet Correlations at the EIC
• TMD factorization for dijets + photon production from the dilute-dense CGC framework
• Resumming subleading Sudakov logarithms in saturation regime
• The color dipole picture for prompt photon production in $pp$ and $pPb$ collisions at the CERN-LHC
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