Observation of charmonium pairs produced exclusively in pp collisions

A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of 3 fb ^-1 collected at centre-of-mass energies of 7 and 8 TeV, J/ψJ/ψ and J/ψψ (2S) pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges (-3.5, -1.5) and (1.5, 5.0). Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be σ ^J/ψJ/ψ = 58 ± 10(stat) ± 6(syst) pb, σ ^J/ψψ(2S) = 63 _-18 ⁺²⁷ (stat) ± 10(syst) pb, σ ^ψ(2S)ψ(2S) < 237 pb, σ ^χc0χc0 < 69 nb, σ ^χc1χc1 < 45 pb, σ ^χc2χc2 141 pb, where the upper limits are set at the 90% confidence level. The measured J/ψJ/ψ and J/ψψ (2S) cross-sections are consistent with theoretical expectations.