Search for doubly charged Higgs boson production in multi-lepton final states with the ATLAS detector using proton-proton collisions at s=13TeV.

TLDR: A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented, fitting the dilepton mass spectra in several exclusive signal regions.

Abstract: A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton–proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to 36.1 $$\text {fb}^{-1}$$ of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays $$H^{\pm \pm }\rightarrow e^{\pm }e^{\pm }$$ , $$H^{\pm \pm }\rightarrow e^{\pm }\mu ^{\pm }$$ and $$H^{\pm \pm }\rightarrow \mu ^{\pm }\mu ^{\pm }$$ , fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section and consequently a lower limit on $$m(H^{\pm \pm })$$ are derived at 95% confidence level. With $$\ell ^{\pm }\ell ^{\pm }=e^{\pm }e^{\pm }/\mu ^{\pm }\mu ^{\pm }/e^{\pm }\mu ^{\pm }$$ , the observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons varies from 770 to 870 GeV (850 GeV expected) for $$B(H^{\pm \pm }\rightarrow \ell ^{\pm }\ell ^{\pm })=100\%$$ and both the expected and observed mass limits are above 450 GeV for $$B(H^{\pm \pm }\rightarrow \ell ^{\pm }\ell ^{\pm })=10\%$$ and any combination of partial branching ratios.