Abstract
In a previous publication, we have presented a model for the photoproduction of $\mathrm{J/}\psi$ vector mesons off protons, where the proton structure in the impact-parameter plane is described by an energy-dependent hot-spot profile. Here we extend this model to study the photonuclear production of $\mathrm{J/}\psi$ vector mesons in coherent and incoherent interactions of heavy nuclei. We study two methods to extend the model to the nuclear case: using the standard Glauber-Gribov formalism and using geometric scaling to obtain the nuclear saturation scale. We find that the incoherent cross section changes sizably with the inclusion of subnucleonic hot spots, and that this change is energy dependent. We propose to search for this behavior by measuring the ratio of the incoherent to coherent cross section at different energies. We compare the results of our model to results from RHIC and from the Run 1 at the LHC finding a satisfactory agreement. We also present predictions for the LHC at the new energies reached in Run 2. The predictions include $\mathrm{J/}\psi$ production in ultra-peripheral collisions, as well as the recently observed photonuclear production in peripheral collisions.
Highlights
Diffractive photoproduction of J /ψ vector mesons in highenergy interactions is a sensitive probe of the gluon distribution of hadrons in the small-x region, where saturation effects are expected to be important [1]
The proton is made up of three hot spots, and the comparisons to experimental data are performed at a fixed center-of-mass energy (Wγp) of the photon-proton system. This model has been extended to the case of photonuclear production at the Large Hadron Collider (LHC) [9]
We present results for the case where the dipole-nucleus cross section was computed with the Glauber-Gribov approach using either a nuclear profile made up of nucleons or of hot spots (GG-n and GG-hs, respectively), as well as for the equivalent calculation performed within the geometric-scaling methodology
Summary
Diffractive photoproduction of J /ψ vector mesons in highenergy interactions is a sensitive probe of the gluon distribution of hadrons in the small-x region, where saturation effects are expected to be important [1]. It has been found that, using a Good-Walker formalism [6], the dissociative photoproduction of J /ψ off proton targets was sensitive to geometric fluctuations of the positions of hot spots in the impact-parameter plane of the interaction [7,8]. In this model, the proton is made up of three hot spots, and the comparisons to experimental data are performed at a fixed center-of-mass energy (Wγp) of the photon-proton system. Another area where such models have been applied is the initial state of collisions involving relativistic nuclei where effects of initial spatial asymmetries may impact on key measurements and their interpretations, e.g., [15,16]
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