University of Birmingham 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 J ψ ψ and J S (2 ) ψψ 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 −+ where the upper limits are set at the 90% con fi dence level. The measured J J ψ ψ and S J (2 ) ψψ cross-sections are consistent with theoretical expectations.