Measurement of exclusive $\gamma\gamma \to \ell\ell$ production in proton-proton collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector

Measurement of the exclusive cross section for the process $\gamma\gamma\to \ell^+\ell^-\;\;(\ell = e,\mu)$ in proton-proton collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector is presented. The cross section in the electron channel is determined to be $\sigma_{\gamma\gamma\to e^+e^-}^\mathrm{excl} = 0.428 \pm 0.035\, \mbox{(stat)} \pm 0.018\, \mbox{(sys)}$ pb in the phase space region with the invariant mass of the electron pair greater that 24 GeV and in which both electrons have transverse momenta $p_\mathrm{T}>12$ GeV and pseudorapidity $|\eta|<2.4$. For muon pairs with invariant mass greater that 20 GeV and both muons having $p_\mathrm{T}>10$ GeV and pseudorapidity $|\eta|<2.4$, the cross section is determined to be $\sigma_{\gamma\gamma\to\mu^+\mu^-}^\mathrm{excl} = 0.628 \pm 0.032\, \mbox{(stat)} \pm 0.021\, \mbox{(sys)}$ pb. The measured cross sections are consistent with QED predictions only if the proton absorptive effects due to finite size of the proton are taken into account.