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

Measurements are presented of the cross-section for the central exclusive production of J/ψ→μ^+μ^- J/ψ→μ+μ− and ψ(2S)→μ^+μ^- 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 2<ημ^± < 4.5 2<ημ±<4.5 ) and mesons in the rapidity range 2.0 < y < 4.5 2.0<y<4.5 . The integrated cross-section results are σJ/ψ→μ^+μ^-(2.0<yJ/ψ<4.5,2.0<η_{μ±} < 4.5) = 400 ± 2 ± 5 ± 12 pb, \ σψ(2S)→μ^+μ^-(2.0<yψ(2S)<4.5,2.0<η_{μ±} < 4.5) = 9.40 ± 0.15 ± 0.13 ± 0.27 pb, σJ/ψ→μ+μ−(2.0<yJ/ψ<4.5,2.0<ημ±<4.5)=400±2±5±12pb,σψ(2S)→μ+μ−(2.0<yψ(2S)<4.5,2.0<ημ±<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 ψ(2S) ψ(2S) and J/ψ 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/ψ J/ψ and ψ(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.