# Doubly-charged Higgs boson at a future electron-proton collider

Dev, P. S. Bhupal (Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130, USA) ; Khan, Sarif (Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India) (Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India) (Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, Göttingen, D-37077 Germany) ; Mitra, Manimala (Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005, India) (Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India) ; Rai, Santosh Kumar (Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India) (Regional Centre for Accelerator-based Particle Physics, Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India) (Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India)

11 June 2019

Abstract: We explore the discovery prospect of the doubly-charged component of an $SU\left(2{\right)}_{L}$-triplet scalar at the future ${e}^{-}p$ collider FCC-eh, proposed to operate with an electron beam energy of 60 GeV and a proton beam energy of 50 TeV. We consider the associated production of the doubly-charged Higgs boson along with leptons and jet(s), and its subsequent prompt decay to same-sign lepton pair. This occurs for $O\left(1\right)$ Yukawa coupling of the scalar triplet with charged leptons, which is expected for reasonably small vacuum expectation values of the neutral component of the triplet field that governs the neutrino mass generation in the type-II seesaw. We present our analysis for two different final states, $3l+\ge 1j$ and an inclusive $\ge 2l+\ge 1j$ channel. Considering its decay to electrons only, we find that the doubly-charged Higgs boson with a mass around a TeV could be observed at the $3\sigma$ confidence level with $O\left(200\right)\text{}\text{}{\mathrm{fb}}^{-1}$ of integrated luminosity, while masses up to 2 TeV could be probed within a few years of data accumulation. The signal proposed here becomes essentially background free, if it is triggered in the $\mu \mu$ mode and a $5\sigma$ discovery is achievable in this channel for a TeV-scale doubly-charged Higgs boson with an integrated luminosity as low as $O\left(50\right)\text{}\text{}{\mathrm{fb}}^{-1}$. We also highlight the sensitivity of FCC-eh to the Yukawa coupling responsible for the production of the doubly-charged Higgs boson as a function of its mass in both the $ee$ and $\mu \mu$ channels.

Published in: Physical Review D 99 (2019)