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 $3{\rm\ fb}^{-1}$ 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 $$ \begin{array}{rl} σ^{J/ψJ/ψ} &= 58\pm10{(\rm stat)} \pm 6{(\rm syst)} {\rm\ pb} , \\ σ^{J/ψψ(2S)} &= 63 ^{+27}_{-18}{(\rm stat)}\pm 10{(\rm syst)} {\rm\ pb} , \\ σ^{ψ(2S)ψ(2S)} &< 237 {\rm\ pb}, \\ σ^{χ_{c0}χ_{c0}} &< 69 {\rm\ nb}, \\ σ^{χ_{c1}χ_{c1}} &< 45 {\rm\ pb}, \\ σ^{χ_{c2}χ_{c2}} &< 141 {\rm\ pb}, \\ \end{array} $$ 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.

21 pages, 5 figures