Photon production in high energy proton-nucleus collisions

We calculate the photon production cross section in $\mathrm{pA}$ collisions under the assumption that the nucleus has reached the saturation regime, while the proton can be described by the standard parton distribution functions. We show that, due to the strong classical field $O(1/g)$ of the nucleus, bremsstrahlung diagrams become dominant over the direct photon diagrams. In particular, we show that $\ensuremath{\gamma}$-jet transverse momentum spectrum and correlations are very sensitive to gluon saturation effects in the nucleus.

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