Search for a light-charged Higgs in a two-Higgs-doublet type II seesaw model at the LHC

A charged Higgs in the type II two-Higgs-doublet model (THDM) has been bounded to be above a few hundred GeV by the radiative B decays. A Higgs triplet extension of the THDM not only provides an origin of neutrino masses and a completely new doubly-charged Higgs decay pattern, but it also achieves a light-charged Higgs with a mass of O(100) GeV through the new scalar couplings in the scalar potential. It was found that these light-charged Higgs decays depend on its mass m_H^± , tan⁡β, and mixing effect sin⁡θ_±: at tan⁡β=1, if m_H^± >m_W+m_Z, b¯bW^±, W^±Z, and τν are the main decay modes; however, if m_H^± <m_W+m_Z, the main decay modes are then b¯bW and τν, and at tan⁡β=30, the τν mode dominates the other decays. When m_t>m_H^± +m_b, we found that the ATLAS and CMS recent upper bounds on the product of BR(t→H⁺b)BR(H⁺→τ⁺ν) can be directly applied and will give a strict constraint on the correlation of m_H^± and sin⁡θ_±. If the upper bound of BR(t→H⁺b)BR(H⁺→τ⁺ν) is satisfied (escaped) for m_t>(<)m_H^± +m_b, it was found that the significance of discovering the charged Higgs through H^±→W^±Z is much lower than that through H^±→b¯bW^±. With a luminosity of 100 fb⁻¹ at s=13 TeV and including the experimental bounds, the significance of the H^±→b¯bW^± signal can reach around 6.2(2.4)σ for m_H^± <(>)m_W+m_Z.