Measurement of exclusive J/ψJ/ 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− and ψ(2S)→μ+μ− processes in proton-proton collisions at √s=13 TeV with 2016–2018 data. They are performed by requiring both muons to be in the LHCb acceptance (with pseudorapidity 2<ημ±<4.5) and mesons in the rapidity range 2.0<y<4.5. The integrated cross-section results are
σJ/ψ→μ+μ−(2.0<yJ/ψ<4.5,2.0<ημ±<4.5)=400±2±5±12 pb,σψ(2S)→μ+μ−(2.0<yψ(2S)<4.5,2.0<ημ±<4.5)=9.40±0.15±0.13±0.27 pb,
where the uncertainties are statistical, systematic and due to the luminosity determination. In addition, a measurement of the ratio of ψ(2S) and J/ψ cross-sections, at an average photon-proton centre-of-mass energy of 1 TeV, is performed, giving σψ(2S)σJ/ψ=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 and ψ(2S) cross-sections on the total transverse momentum transfer is determined in pp collisions and is found consistent with the behaviour observed in electron-proton collisions.