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

This Letter reports a measurement of the exclusive γγ→ℓ+ℓ−γγ→ℓ+ℓ− (ℓ=e, μℓ=e, μ) cross-section in proton–proton collisions at a centre-of-mass energy of 7 TeV7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb−14.6 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 σγγ→e+e−excl.=0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb for a phase–space region with invariant mass of the electron pairs greater than 24 GeV24 GeV, in which both electrons have transverse momentum pT>12 GeVpT>12 GeV and pseudorapidity |η|<2.4|η|<2.4. For muon pairs with invariant mass greater than 20 GeV20 GeV, muon transverse momentum pT>10 GeVpT>10 GeV and pseudorapidity |η|<2.4|η|<2.4, the cross-section is determined to be σγγ→μ+μ−excl.=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.