# Identifying a light charged Higgs boson at the LHC Run II

## TL;DR

This paper explores the detection prospects of a light charged Higgs boson in the 2HDM Type-I at LHC Run II, focusing on a novel decay channel involving a fermiophobic Higgs and multiple photons, which could produce a distinctive experimental signature.

## Contribution

It identifies parameter regions where the charged Higgs decays predominantly via a bosonic channel, proposing a new search strategy involving multiple photons at the LHC.

## Key findings

- The $H^ o W^{ o} h$ decay can dominate over traditional modes.
- The $h$ can be highly fermiophobic with a large $ o o o o$ decay rate.
- The cross section for $pp o H^ o h o W + 4 ext{ photons}$ can reach up to 100 fb.

## 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 ${\cal O}(100~{\rm fb}^{-1})$ as luminosity. When sufficiently light, this $h$ state can open up the bosonic decay channel $H^\pm \to W^{\pm(*)}h$, 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 $H^\pm \to W^{\pm(*)}h$ 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 $\sigma(pp\to H^\pm h \to W^{\pm(*)} + 4\gamma)$ process reaching up to ${\cal O}(100~{\rm fb})$. We therefore investigate the possibility of observing this spectacular signal at the LHC Run II.