Measurement of exclusive γγ → ` ` production in proton-proton collisions at √ s = 7 TeV with the ATLAS detector

Measurement of the exclusive cross section for the process γγ→ `+`− (` = e,μ) in proton-proton collisions at √ s = 7 TeV with the ATLAS detector at the LHC is presented. The cross section in the electron channel is determined to be σ excl γγ→e+e− = 0.428± 0.035(stat)± 0.018(sys) pb in the phase space region with the invariant mass of the electron pair greater than 24 GeV and in which both electrons have transverse momenta pT > 12 GeV and pseudorapidity |η | < 2.4. For muon pairs with invariant mass greater than 20 GeV and both muons having pT > 10 GeV and pseudorapidity |η |< 2.4, the cross section is determined to be σ excl γγ→μ+μ− = 0.628±0.032(stat)± 0.021(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.