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We present a study of the central exclusive production (CEP) of meson pairs 1 , M M , at sufficiently high invariant mass that a perturbative QCD formalism is applicable. Within this framework, M M production proceeds via the gg → M M hard scattering sub-process, which can be calculated within the hard exclusive formalism. We present explicit calculations for the gg → M M helicity amplitudes for different meson states and, using these, show results for meson pair CEP in the perturbative regime. a KRYSTHAL collaboration b speaker

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Motivated by the recent experimental observation of exclusive χ c events at the Tevatron, we revisit earlier studies of central exclusive scalar χ c0 meson production, before generalising the existing formalism to include χ c1 and χ c2 mesons. Although χ c0 production was previously assumed to be dominant, we find that the χ c1 and χ c2 rates for the experimentally considered χ c → J/ψγ → µ + µ − γ decay process are in fact comparable to the χ c0 rate. We have developed a new Monte Carlo event generator, SuperCHIC, which models the central exclusive production of the three χ c states via this decay chain, and have explored possible ways of distinguishing them, given that their mass differences are not resolvable within the current experimental set-up. Although we find that the severity of current experimental cuts appears to preclude this, the acceptance does not change crucially between the three states and so our conclusions regarding the overall rates remain unchanged. This therefore raises the interesting possibility that exclusive χ c1 and χ c2 production has already been observed at the Tevatron.2 In the χc case the agreement becomes especially striking after taking into account the revised value of the total χc0 width which has been reduced by a factor 1.4 [37] as compared to the value in the Review of Particle Properties (2002) used in [5].3 CHIC is a publicly available Monte Carlo implementation of the χc0 analysis of Ref. [5]. 4 This applies not only to χc(1P ) states, but also to possible higher excitations χc(nP ). 5 S enh is largely independent of the χ spin assignment. Note also that the relative number of events where the forward protons dissociate is larger for χc1 and χc2 than for χc0.