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

Abstract

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 $\mathcal{O}(100)$ GeV through the new scalar couplings in the scalar potential. It was found that these light-charged Higgs decays depend on its mass $m_{H^{\pm }}$, $\tan \beta$, and mixing effect $\sin {\theta }_{\pm }$: at $\tan \beta =1$, if $m_{H^{\pm }}>m_W+m_Z$, $\bar{b}b{W}^{\pm }$, $W^{\pm }Z$, and $\tau \nu$ are the main decay modes; however, if $m_{H^{\pm }}<m_W+m_Z$, the main decay modes are then $\bar{b}bW$ and $\tau \nu$, and at $\tan \beta =30$, the $\tau \nu$ mode dominates the other decays. When $m_t>m_{H^{\pm }}+m_b$, we found that the ATLAS and CMS recent upper bounds on the product of $BR(t\to H^{+}b)BR(H^{+}\to {\tau }^{+}\nu )$ can be directly applied and will give a strict constraint on the correlation of $m_{H^{\pm }}$ and $\sin {\theta }_{\pm }$. If the upper bound of $BR(t\to H^{+}b)BR(H^{+}\to {\tau }^{+}\nu )$ is satisfied (escaped) for $m_t>(<)m_{H^{\pm }}+m_b$, it was found that the significance of discovering the charged Higgs through $H^{\pm }\to W^{\pm }Z$ is much lower than that through $H^{\pm }\to \bar{b}b{W}^{\pm }$. With a luminosity of 100 fb${}^{-1}$ at $\sqrt{s}=13$ TeV and including the experimental bounds, the significance of the $H^{\pm }\to \bar{b}b{W}^{\pm }$ signal can reach around $6.2(2.4)\sigma$ for $m_{H^{\pm }}<(>)m_W+m_Z$.

Comments: 16 pages, 5 figures, 4 tables, version accepted for publication in Physics Letters B