Measuring gluon shadowing with prompt photons at RHIC and LHC

Abstract

The possibility to observe the nuclear modification of the gluon distribution at small-x (gluon shadowing) using high-p_T prompt photon production at RHIC and at LHC is discussed. The per-nucleon ratio, sigma(p+A -> gamma+X) / A sigma(p+p -> gamma+X), is computed for both inclusive and isolated prompt photons in perturbative QCD at NLO using different parametrizations of nuclear parton densities, in order to assess the visibility of the shadowing signal. The production of isolated photons turns out to be a promising channel which allows for a reliable extraction of the gluon density, G^A/G^p, and the structure function, F_2^A/F_2^p, in a nucleus over that in a proton. Moreover, the production ratio of prompt photons at forward-over-backward rapidity in p-A collisions provides an estimate of G^A/G^p (at small x) over F_2^A/F_2^p (at large x), without the need of p-p reference data at the same energy.

14 pages, 6 figures. Typo corrected in Eq. (4)

References in corpus (2)

• A new critical study of photon production in hadronic collisions
• Hard probes in heavy ion collisions at the LHC: PDFs, shadowing and $pA$ collisions

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• Nuclear shadowing and prompt photons at relativistic hadron colliders
• Constraints on nuclear gluon densities from J/psi data
• Predictions for the isolated prompt photon production at the LHC at $\sqrt{s}=$13 TeV
• DDVCS on nucleons and nuclei
• Shadowing in Compton scattering on nuclei
• Drell-Yan process in $pA$ collisions: the exact treatment of coherence effects
• Nuclear gluons at RHIC in a multi-observable approach