Search for third-generation scalar leptoquarks decaying to a top quark and a $\tau$ lepton at $\sqrt{s}=$ 13 TeV

Bakhshiansohi, Hamed [UCL] Bondu, Olivier [UCL] Brochet, Sébastien [UCL] Bruno, Giacomo [UCL] Caputo, Claudio [UCL] Caudron, Adrien [UCL] David, Pieter [UCL] De Visscher, Simon [UCL] Delaere, Christophe [UCL] Delcourt, Martin [UCL] Francois, Brieuc [UCL] Giammanco, Andrea [UCL] Krintiras, Georgios [UCL] Lemaitre, Vincent [UCL] Magitteri, Alessio [UCL] Mertens, Alexandre [UCL] Musich, Marco [UCL] Piotrzkowski, Krzysztof [UCL] Quertenmont, Loic [UCL] Saggio, Alessia [UCL] Vidal Marono, Miguel [UCL] Wertz, Sébastien [UCL] Zobec, Joze [UCL] et al.

A search for pair production of heavy scalar leptoquarks (LQs), each decaying into a top quark and a $\tau$ lepton, is presented. The search considers final states with an electron or a muon, one or two $\tau$ leptons that decayed to hadrons, and additional jets. The data were collected in 2016 in proton-proton collisions at $\sqrt{s}=$ 13 TeV with the CMS detector at the LHC, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. No evidence for pair production of LQs is found. Assuming a branching fraction of unity for the decay LQ$ \to $t$\tau$, upper limits on the production cross section are set as a function of LQ mass, excluding masses below 900 GeV at 95% confidence level. These results provide the most stringent limits to date on the production of scalar LQs that decay to a top quark and a $\tau$ lepton.