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/ψ J/ψ and J/ψ ψ(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/ψ J/ψ} = 58 ± 10(stat) ±6 (syst) pb, σ^{J/ψ ψ(2S)} = 63{−18}{+27}(stat) ± 10(syst) pb, σ^{ψ(2S) ψ(2S)} < 237 pb, σ^{χc0 χc0} < 69 nb, σ^{χc1 χc1} < 45 pb, σ^{χc2 χc2} < 141 pb, where the upper limits are set at the 90% confidence level. The measured J/ψ J/ψ and J/ψ ψ(2S) cross-sections are consistent with theoretical expectations.