Slight excess at 130 GeV in search for a charged Higgs boson decaying to a charm quark and a bottom quark at the Large Hadron Collider

Abstract

Searches for a charged Higgs boson (H ±) decaying to a charm quark and a bottom quark (H ± → cb) have been carried out at the Large Hadron Collider (LHC) in the decay of top quarks (t → H ± b). In a recent search by the ATLAS collaboration (with all run II data, 139 fb−1) a local excess of around 3σ has been observed, which is best fitted by a charged Higgs boson with a mass of around 130 GeV and a product of branching ratios (BRs) given by BR(t → H ± b) × BR(H ± → cb) = 0.16% ± 0.06%. In the context of two-Higgs-doublet models (2HDM) with independent Yukawa couplings for H ± we present the parameter space for which this excess (assuming it to be genuine) can be accommodated, taking into account the limits from LHC searches for H ± → cs and H ± → τν at = 130 GeV and the constraint from b → sγ. It is then shown that such an excess cannot be explained in 2HDMs with natural flavour conservation, but can be accommodated in the flipped three-Higgs-doublet model (3HDM) and in the aligned 2HDM (A2HDM). Upcoming searches with 139 fb−1 in the channels H ± → cb (CMS), H ± → cs (ATLAS/CMS) and H ± → τν (ATLAS/CMS) will determine if the excess is the first sign of an H ± with GeV.