Measurement of exclusive γ γ → l+l− production in proton–proton collisions at √s = 7 TeV with the ATLAS detector

Abstract

This Letter reports a measurement of the exclusive γ γ → l+l− (l = e, μ) cross-section in proton–proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb−1. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be σexcl. + − =0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb γγ→e e for a phase–space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum pT > 12 GeV and pseudorapidity |η| < 2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum 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 (syst.) pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.