Energy dependence of exclusive $J/\psi $ photoproduction off protons in ultra-peripheral p–Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02$ TeV

The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of $J/\psi $ vector mesons off proton targets in ultra–peripheral p–Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{{s}_{\mathrm{NN}}}=5.02$ TeV. The e ${}^{+}$ e ${}^{-}$ and ${\mu }^{+}{\mu }^{-}$ decay channels are used to measure the cross section as a function of the rapidity of the $J/\psi $ in the range $-2.5