Identifying a light charged Higgs boson at the LHC Run II

Abstract

We analyse the phenomenological implications of a light Higgs boson, $h$, within the CP-conserving 2-Higgs Doublet Model (2HDM) Type-I, for the detection prospects of the charged $H^{\pm }$ state at Run II of the Large Hadron Collider (LHC), assuming $\sqrt{s}=13$ TeV as energy and $\mathcal{O}(100{\mathrm{fb}}^{-1})$ as luminosity. When sufficiently light, this $h$ state can open up the bosonic decay channel $H^{\pm }\to W^{\pm (\ast )}h$, which may have a branching ratio significantly exceeding those of the $H^{\pm }\to \tau \nu$ and $H^{\pm }\to cs$ channels. We perform a broad scan of the 2HDM Type-I parameter space, assuming the heavier of the two CP-even Higgs bosons, $H$, to be the observed SM-like state with a mass near 125 GeV. Through these scans we highlight regions in which $m_{H^{\pm }}<m_t+m_b$ that are still consistent with the most recent limits from experimental searches. We find in these regions that, when the $H^{\pm }\to W^{\pm (\ast )}h$ decay mode is the dominant one, the $h$ can be highly fermiophobic, with a considerably large decay rate in the $\gamma \gamma$ channel. This can result in the total cross section of the $\sigma (pp\to H^{\pm }h\to W^{\pm (\ast )}+4\gamma )$ process reaching up to $\mathcal{O}(100\mathrm{fb})$. We therefore investigate the possibility of observing this spectacular signal at the LHC Run II.

Comments: 11 pages, 7 figures