Observation of charmonium pairs produced exclusively in pp collisions

Abstract

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 Jψ ψ and J S ψψ (2 ) 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 58 10(stat) 6(syst) pb, 63 (stat) 10(syst) pb, 237 pb, 69 nb, 45 pb, 141 pb, S S S J J J (2 ) 18 27 (2 ) (2 ) c0 c0 c1 c1 c2 c2 σ σ σ σ σ σ =± ± = ± < < < < ψ ψ ψψ ψ ψ χ χ χ χ χ χ − + 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.