Measurement of exclusive J/ and (2S) production at s=13 TeV

Measurements are presented of the cross-section for the central exclusive production of J/^+^- J/ψ→μ+μ− and (2S) ^+^- ψ (2S) →μ+μ− processes in proton-proton collisions at s = 13 \ TeV s=13TeV with 2016–2018 data. They are performed by requiring both muons to be in the LHCb acceptance (with pseudorapidity 22ημ±4. 5) and mesons in the rapidity range 2. 0 2. 0y4. 5. The integrated cross-section results are ₉/^+^- (2. 0σJ/ψ→μ+μ− (2. 0yJ/ψ4. 5, 2. 0ημ±4. 5) =400±2±5±12pb, σψ (2S) →μ+μ− (2. 0yψ (2S) 4. 5, 2. 0ημ±4. 5) =9. 40±0. 15±0. 13±0. 27pb, where the uncertainties are statistical, systematic and due to the luminosity determination. In addition, a measurement of the ratio of (2S) ψ (2S) and J/ J/ψ cross-sections, at an average photon-proton centre-of-mass energy of 1\ TeV 1TeV, is performed, giving = 0. 1763 ± 0. 0029 ± 0. 0008 ± 0. 0039, where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the involved branching fractions. For the first time, the dependence of the J/ J/ψ and (2S) ψ (2S) cross-sections on the total transverse momentum transfer is determined in pp pp collisions and is found consistent with the behaviour observed in electron-proton collisions.