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 super(-1) collected at centre-of-mass energies of 7 and 8 TeV, J/[psi]J/[psi] and J/[psi][psi](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 [sigma] super(J/[psi]J/[psi]) = 58 + or - 10(stat) + or - 6(syst) pb, [sigma] super(J/[psi][psi](2S)) = (ProQuest: Formulae and/or non-USASCII text omitted) + or - 10(syst) pb, [sigma] super([psi](2S)[psi](2S)) < 237 pb, [sigma] super( chi c0 chi c0) < 69 nb, [sigma] super( chi c1 chi c1) < 45 pb, [sigma] super( chi c2 chi c2) < 141 pb, where the upper limits are set at the 90% confidence level. The measured J/[psi]J/[psi] and J/[psi][psi]/(2S) cross-sections are consistent with theoretical expectations.