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

AbstractThe production of a pair of τ leptons via photon–photon fusion,γγ→ττ, 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 ofγγ→ττisσobsfid=12.4−3.1+3.8fb. Constraints are set on the contributions to the anomalous magnetic moment (aτ) and electric dipole moments (dτ) of the τ lepton originating from potential effects of new physics on theγττvertex:aτ=0.0009−0.0031+0.0032and-dτ-<2.9×10−17ecm(95% confidence level), consistent with the standard model.

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