Energy dependence of dissociative $J/\psi$ photoproduction as a signature of gluon saturation at the LHC

Abstract

We have developed a model in which the quantum fluctuations of the proton structure are characterised by hot spots, whose number grows with decreasing Bjorken-$x$. Our model reproduces the $F_2(x,Q^2)$ data from HERA at the relevant scale, as well as the exclusive and dissociative $J/\psi$ photoproduction data from H1 and ALICE. Our model predicts that for $W_{\gamma \mathrm{p}}\approx 500$ GeV, the dissociative $J/\psi$ cross section reaches a maximum and then decreases steeply with energy, which is in qualitatively good agreement to a recent observation that the dissociative $J/\psi$ background in the exclusive $J/\psi$ sample measured in photoproduction by ALICE decreases as energy increases. Our prediction provides a clear signature for gluon saturation at LHC energies.

Comments: 10 pages plus references, 3 figures. This version matches accepted version