Measurement of the $Z/ \gamma^* \rightarrow \tau \tau$ cross section in pp collisions at $\sqrt{s}=$ 13 TeV and validation of $\tau$ lepton analysis techniques

Abstract

A measurement is presented of the $Z/ \gamma^* \rightarrow \tau \tau$ cross section in pp collisions at $\sqrt{s}=$ 13 TeV, using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.3 $fb^{-1}$. The product of the inclusive cross section and branching fraction is measured to be $\sigma(pp \rightarrow Z / \gamma^* + X)B(Z / \gamma^* \rightarrow \tau \tau) = 1848 ± 12 (\text{stat}) ± 67 (\text{syst+lumi})$ pb, in agreement with the standard model expectation, computed at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. The measurement is used to validate new analysis techniques relevant for future measurements of τ lepton production. The measurement also provides the reconstruction efficiency and energy scale for $\tau$ decays to hadrons+$\nu_\tau$ final states, determined with respective relative uncertainties of 2.2% and 0.9%.