Energy dependence of exclusive J/ψ photoproduction off protons in ultra-peripheral p–Pb collisions at √sNN = 5.02 TeV

The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of J/ψ vec- tor mesons off proton targets in ultra–peripheral p–Pb colli- sions at a centre-of-mass energy per nucleon pair √sNN = 5.02 TeV. The e+ e− and μ+ μ− decay channels are used to measure the cross section as a function of the rapidity of the J/ψ in the range −2.5 < y < 2.7, correspond- ing to an energy in the γp centre-of-mass in the interval 40 < Wγ p < 550 GeV. The measurements, which are consis- tent with a power law dependence of the exclusive J/ψ pho- toproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measure- ments.