$\tau^\pm \nu \gamma\gamma$ and $\ell^\pm \ell^\pm \gamma \gamma {\rlap{\,/}{E}_T} X$ to probe the fermiophobic Higgs boson with high cutoff scales

Abstract

The light fermiophobic Higgs boson $h_{\rm f}$ in the type-I two-Higgs-doublet model can evade the current search programs at the LHC since its production through the quark-antiquark annihilation and gluon fusion is not feasible. The particle can be more elusive if the model retains stability up to the Planck scale because the efficient discovery channels are missing from the existing search chart. Through the comprehensive scanning, we show that all the viable parameter points with the Planck cutoff scale require $ m_{h_{\rm f}} \in[80,\, 120]{\;{\rm GeV}}$ and $M_{A/H^\pm} \in [90,\,150]{\;{\rm GeV}}$. Since $h_{\rm f}h_{\rm f}\to \gamma\gamma W^+ W^-$ and $H^\pm \to \tau^\pm \nu/h_{\rm f}W^\pm$ are dominant in this case, two final states are more efficient to probe $h_{\rm f}$ than the conventional search mode of $4\gamma+W^\pm/Z$. One is $\tau^\pm\nu \gamma\gamma$ from $pp \to H^\pm(\to\tau^\pm\nu) h_{\rm f}(\to \gamma\gamma)$ and the other is $\ell^\pm \ell^\pm \gamma\gamma {\rlap{\,/}{E}_T} X$ ($\ell^\pm=e^\pm,\mu^\pm$) from $pp \to H^\pm(\to h_{\rm f}W^\pm) h_{\rm f} \to \gamma\gamma W^+ W^-W^\pm $, $pp \to H^\pm(\to h_{\rm f} W^\pm) A(\to h_{\rm f} Z) \to \gamma\gamma W^+ W^- W^\pm Z $, and $pp \to H^+(\to h_{\rm f} W^+)H^-(\to h_{\rm f} W^-)\to \gamma\gamma W^+ W^- W^+ W^-$. The inclusive $\ell^\pm \ell^\pm \gamma\gamma {\rlap{\,/}{E}_T} X$ consists of a same-sign dilepton, two prompt photons, and missing transverse energy. We perform the signal-background analysis at the detector level. With the total integrated luminosity of $300\;{\rm fb}^{-1}$ and the 5\% background uncertainty, two proposed channels at the 14 TeV LHC yield signal significances above five in the entire viable parameter space of the fermiophobic type-I with a high cutoff scale.