Bounds on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario

A direct search for doubly-charged Higgs bosons $H^{\pm\pm}$ is one of the most important probe in the Higgs Triplet Model, which is motivated by generation mechanisms of tiny neutrino masses. There are two major decay modes of $H^{\pm\pm}$; i.e., the same-sign dilepton decay $H^{\pm\pm}\to\ell^\pm\ell^\pm$ and the same-sign diboson decay $H^{\pm\pm}\to W^{\pm(*)}W^{\pm(*)}$. For the case where the former decay mode is dominant, the lower limit on the mass of $H^{\pm\pm}$ has been set at about 400 GeV by ATLAS and CMS Collaborations. On the other hand, for the case where the latter decay mode is dominant, no dedicated search has been performed in the past. By taking into account characteristic signals of $H^{\pm\pm}$ in the diboson decay scenario at LEP and the LHC experiments, we find that the lower mass bound of 60-68 GeV can be obtained using the same-sign dilepton search performed by ATLAS Collaboration with 4.7 fb$^{-1}$ data at the collision energy of 7 TeV. We also show that the limit can be extended up to about 85-90 GeV, assuming the integrated luminosity of 20 fb$^{-1}$ and 7 TeV for the collision energy. We give detailed explanations on the decay properties of $H^{\pm\pm}$ for relatively small mass cases and also on production cross sections of $H^{\pm\pm}$ at the next-to-leading order of QCD at the LHC.