Observation of $\gamma \gamma$ $\to$ $\tau \tau$ in proton-proton collisions and limits on the anomalous electromagnetic moments of the $\tau$ lepton

Abstract

The production of a pair of $\tau$ leptons via photon-photon fusion, $\gamma \gamma$ $\to$ $\tau \tau$, 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 $\tau$ 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 $\tau$ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of $\gamma \gamma$ $\to$ $\tau \tau$ is ${\sigma }_{\text{obs}}^{\text{fid}}$ = 12.4 ${}_{-3.1}^{+3.8}$ fb. Constraints are set on the contributions to the anomalous magnetic moment ($a_{\tau }$) and electric dipole moments ($d_{\tau }$) of the $\tau$ lepton originating from potential effects of new physics on the $\gamma \tau \tau$ vertex: $a_{\tau }$ = 0.0009 ${}_{-0.0031}^{+0.0032}$ and $|d_{\tau }|$ $<$ 2.9 $\times$ 10${}^{-17}$ $e$cm (95% confidence level), consistent with the standard model.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables, including additional supplementary figures, can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/SMP-23-005 (CMS Public Pages)

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