Observation of ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">; <mml:mrow>; <mml:mrow>; <mml:mtext>γ</mml:mtext>; <mml:mtext>γ</mml:mtext>; <mml:mo>→</mml:mo>; <mml:mtext>τ</mml:mtext>; <mml:mtext>τ</mml:mtext>; </mml:mrow>; </mml:mrow>; </mml:math>; in proton–proton collisions and limits on the anomalous electromagnetic moments of the τ lepton | CU Experts

Abstract; The production of a pair of τ leptons via photon–photon fusion, ; ; ; ; ; ; γ; γ; →; τ; τ; ; ; ; ; , is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb−1. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of ; ; ; ; ; ; γ; γ; →; τ; τ; ; ; ; ; is ; ; ; ; ; σ; obs; fid; ; =; ; 12.4; ; −; 3.1; ; ; +; 3.8; ; ; ; fb; ; ; . Constraints are set on the contributions to the anomalous magnetic moment (; ; ; ; ; ; a; ; τ; ; ; ; ; ; ) and electric dipole moments (; ; ; ; ; ; d; ; τ; ; ; ; ; ; ) of the τ lepton originating from potential effects of new physics on the ; ; ; ; γ; τ; τ; ; ; vertex: ; ; ; ; ; ; a; ; τ; ; ; ; =; ; 0.0009; ; −; 0.0031; ; ; +; 0.0032; ; ; ; ; and ; ; ; ; -; ; ; d; ; τ; ; ; ; ; -; ; <; 2.9; ×; ; 10; ; −; 17; ; ; ; ; e; ; ; cm; ; ; (95% confidence level), consistent with the standard model.

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