Measurement of the exclusive two-photon production of muon pairs at the LHC

A measurement is reported of the exclusive two-photon production of muon pairs, $pp \rightarrow p \mu^{+}\mu^{-} p$, in proton-proton collisions at $\sqrt{s}= 7$~TeV for an integrated luminosity of $40$~pb$^{-1}$. For muon pairs with invariant mass above $11.5$~GeV, and with $p_T(\mu) > 4$~GeV and $|\eta(\mu)| < 2.1$, a fit to the $p_{T}(\mu^{+}\mu^{-})$ distribution results in a measured partial cross-section of $\sigma(pp \rightarrow p \mu^{+}\mu^{-} p) = 3.38^{+0.58}_{-0.55} (stat.) \pm 0.16 (syst.) \pm 0.14 (lumi)$~pb. The ratio to the predicted value is $0.83^{+0.14}_{-0.13} (stat.) \pm 0.04 (syst.)$. The statistical uncertainties are correlated with the single proton dissociation background, with values of the signal yield ratio between 0.64 and 1.03 contained within the 1$\sigma$ region. The characteristic distributions of the muon pairs produced via $\gamma\gamma$ fusion, such as the muon acoplanarity, the muon pair invariant mass and transverse momentum, are well described by the full detector simulation using the \textsc{Lpair} event generator.