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arXiv · 1610.03350

Small $x$ gluon shadowing from LHC data on coherent $\mathrm{J/}ψ$ photoproduction

J. G. Contreras
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Abstract

The cross section for coherent $\mathrm{J/}ψ$ photoproduction in Pb-Pb collisions is the sum of two contributions, one from low-, the other from high-energy photon-nucleus interactions. A novel method to disentangle both contributions allowing one to extract the coherent photo-nuclear cross section for coherent $\mathrm{J/}ψ$ production, $σ_{γ\rm Pb}$, is presented. The utility of the method is demonstrated using measurements from peripheral and ultra-peripheral Pb-Pb collisions at the LHC. Applying the proposed method to the available data it is possible to obtain $σ_{γ\rm Pb}$ up to a photon-lead centre-of-mass energy of 470 GeV, which corresponds to $x$ of 4.4x10$^{-5}$. To illustrate a possible use of the extracted photo-nuclear cross sections, the corresponding nuclear suppression factors are computed and they are compared to predictions of gluon shadowing calculated in the leading-twist approximation approach.

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J. G. Contreras. 2017-07-13. Small $x$ gluon shadowing from LHC data on coherent $\mathrm{J/}ψ$ photoproduction. https://doi.org/10.1103/physrevc.96.015203

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