Observation of $\tau$ lepton pair production in ultraperipheral lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

Abstract

We present an observation of photon-photon production of $\tau$ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 $\mu$b${}^{-1}$ collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The $\gamma \gamma$ $\to$ ${\tau }^{+}{\tau }^{-}$ process is observed for $\tau \tau$ events with a muon and three charged hadrons in the final state. The measured fiducial cross section is $\sigma (\gamma \gamma$ $\to$ ${\tau }^{+}{\tau }^{-})$ = 4.8 $\pm$ 0.6 (stat) $\pm$ 0.5 (syst) $\mu$b, in agreement with leading-order QED predictions. Using $\sigma (\gamma \gamma$ $\to$ ${\tau }^{+}{\tau }^{-})$, we estimate a model-dependent value of the anomalous magnetic moment of the $\tau$ lepton of $a_{\tau }$ = 0.001 ${}_{-0.089}^{+0.055}$.

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/HIN-21-009 (CMS Public Pages)

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