Search for direct $\tau$ slepton pair production in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$

A search for $\tau$ slepton pair production in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of $77.2~\mathrm{fb}^{-1}$ collected with the CMS detector in 2016 and 2017. The search is carried out in events with a pair of $\tau$ leptons in the final state, expected from each $\tau$ slepton decaying into a $\tau$ lepton and a neutralino. We consider events in which both $\tau$ leptons decay hadronically, as well as events in which one of the $\tau$ leptons decays hadronically while the other decays to an electron or a muon. The observed data are consistent with the standard model background expectation, and the results are interpreted as upper limits on the cross section for $\tau$ slepton pair production in different scenarios. In the scenario of a purely left-handed $\tau$ slepton decaying to a nearly massless neutralino, the strongest limits are obtained for a $\tau$ slepton mass of 125 GeV, corresponding to 1.14 times the theoretical cross section.