Search for doubly-charged Higgs boson in multi-lepton final states at $\sqrt{s}$= 13 TeV with the ATLAS detector

A search for new high mass resonances decaying to two high-$p_T$ leptons with same-charge is presented. The results reported here use the $pp$ collision data sample corresponding to 36.1 fb$^{−1}$ of integrated luminosity collected in 2015 and 2016 by the ATLAS detector at the LHC with a centre-of-mass energy of 13 TeV. The benchmark model is doubly charged Higgs boson (DCH) production via Drell--Yan with subsequent exclusive decay into leptons. Leptonic final states are very interesting since they provide a good sensitivity and small systematic uncertainties. In addition, requiring same-sign leptonic final states reduces the background contamination from Standard Model processes while providing a large sensitivity to Beyond Standard Model phenomena. No significant evidence of a signal was observed and corresponding limits on the production cross-section and a lower limit on $m(H^{\pm\pm})$ were derived at 95% confidence level. The results at $\sqrt{s}$ = 13 TeV complement and improve former ones obtained by the ATLAS Collaboration with a LHC centre-of-mass energy of $\sqrt{s}$ = 8 TeV