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 $3{\mathrm{fb}}^{-1}$ collected at centre-of-mass energies of 7 and 8 TeV, $J/\ddot{I}ˆJ/\ddot{I}ˆ$ and $J/\ddot{I}ˆ\ddot{I}ˆ(2S)$ 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 $$\begin{array}{rl}\ddot{I}{ƒ}^{J/\ddot{I}ˆJ/\ddot{I}ˆ}& =58\pm 10(\mathrm{stat})\pm 6(\mathrm{syst})\mathrm{pb},\\ \ddot{I}{ƒ}^{J/\ddot{I}ˆ\ddot{I}ˆ(2S)}& =63_{-18}^{+27}(\mathrm{stat})\pm 10(\mathrm{syst})\mathrm{pb},\\ \ddot{I}{ƒ}^{\ddot{I}ˆ(2S)\ddot{I}ˆ(2S)}& <237\mathrm{pb},\\ \ddot{I}{ƒ}^{\ddot{I}{‡}_{c0}\ddot{I}{‡}_{c0}}& <69\mathrm{nb},\\ \ddot{I}{ƒ}^{\ddot{I}{‡}_{c1}\ddot{I}{‡}_{c1}}& <45\mathrm{pb},\\ \ddot{I}{ƒ}^{\ddot{I}{‡}_{c2}\ddot{I}{‡}_{c2}}& <141\mathrm{pb},\end{array}$$ where the upper limits are set at the 90% confidence level. The measured $J/\ddot{I}ˆJ/\ddot{I}ˆ$ and $J/\ddot{I}ˆ\ddot{I}ˆ(2S)$ cross-sections are consistent with theoretical expectations.

21 pages, 5 figures