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 ($H^\pm$) decaying to a charm quark and a bottom quark ($H^\pm \to cb$) have been carried out at the Large Hadron Collider (LHC) in the decay of top quarks ($t\to H^\pm b$). In a recent search by the ATLAS collaboration (with all Run II data, 139 fb$^{-1}$) a local excess of around $3\sigma$ has been observed, which is best fitted by a charged Higgs boson with a mass ($m_{H^\pm}$) of around 130 GeV and a product of branching ratios (BRs) given by BR$(t\to H^\pm b)\times{\rm BR}(H^\pm\to cb)=0.16\%\pm 0.06\%$. In the context of Two-Higgs-Doublet Models (2HDM) with independent Yukawa couplings for $H^\pm$ 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 $H^\pm\to cs$ and $H^\pm\to \tau\nu$ at $m_{H^\pm}$=130 GeV and the constraint from $b\to s\gamma$. 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 $H^\pm\to cb$ (CMS), $H^\pm \to cs$ (ATLAS/CMS) and $H^\pm \to \tau\nu$ (ATLAS/CMS) will determine if the excess is the first sign of an $H^\pm$ with $m_{H^\pm}=130$ GeV.

The flavor of a light charged Higgs

“…Where our study overlaps the one in ref. [2], we confirm their results. In particular, we confirm that two Higgs doublet models (2HDMs) with NFC cannot explain the signal, while a three-Higgs doublet model (3HDM), where each fermion sector couples to a different Higgs doublet, can do so.…”

“…Some quantitative differences in this context arise because we use updated experimental constraints on the b → sγ decay, which are considerably stronger than the ones used in ref. [2].…”

Signature of a light charged Higgs boson from top quark pairs at the LHC

“…The searches of a light charged Higgs boson at the LHC, namely with mass smaller than difference of the masses of the top quark and the bottom quark, benefit from the large production cross sections of the top quark pair which decays into the charged Higgs boson and a bottom quark. A light charged Higgs boson can undertake several possible decays [10][11][12][13], for instance in the 2HDMs into τ + ν τ , cs, c b, t ( * )b , and W + A if the mass of the CP-odd Higgs boson A is below the threshold. The later two decays can both lead to W + b b final states either directly or via cascade decay of A, which can be dominant over the two-body decays.…”