Central exclusive dimuon production at LHCb

Preliminary cross section measurements are presented for central exclusive production of non-resonant dimuons, $J/\psi (2S)$ and $\chi_c$. Candidate events are selected by requiring that only the signal process is present in the pseudorapidity range 1.9 < $\eta$ < 4.9, and that there is no activity in the range -4 < $\eta$ < -1.5 The cross sections for $J/\psi (2S)$ and $\chi_c$ are found to be in broad agreement with theoretical predictions, and the cross section for non-resonant dimuon production is consistent with the precise prediction available for this process.