Measurement of exclusive $\gamma\gamma \rightarrow \mu^+\mu^-$\\ production at $\sqrt{s}=7$ TeV

The first measurement of the exclusive two-photon production of muon pairs, $pp \rightarrow p \mu^{+}\mu^{-} p$, in proton-proton collisions at $\sqrt{s}= 7$~TeV has been recently achieved with 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 $I\eta(\mu)I < 2.1$, 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 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 LPAIR event generator. This opens the way for an unique and precise integrated luminosity calibration at the LHC.