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

Abstract

This Letter reports a measurement of the exclusive $\gamma \gamma \to {\ell }^{+}{\ell }^{-}(\ell =e,\mu )$ 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 ${\sigma }_{\gamma \gamma \to e^{+}{e}^{-}}^{excl.}=0.428\pm 0.035(stat.)\pm 0.018(syst.)$ pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum $p_{\mathrm{T}}>12$ GeV and pseudorapidity $|\eta |<2.4$. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum $p_{\mathrm{T}}>10$ GeV and pseudorapidity $|\eta |<2.4$, the cross-section is determined to be ${\sigma }_{\gamma \gamma \to {\mu }^{+}{\mu }^{-}}^{excl.}=0.628\pm 0.032(stat.)\pm 0.021(syst.)$ 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.

12 pages + references + author list + cover pages (34 pages total), 4 figures, 3 tables, submitted to Phys. Lett. B, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2014-13/

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