Discovery prospects for the 150 GeV charged scalar at future $$e^+e^-$$ colliders

Abstract The Real Higgs Triplet model, known as the $$\varDelta $$ Δ SM, is a minimal extension of the Standard Model (SM) obtained by adding a hypercharge 0 triplet ( $$\varDelta $$ Δ ). This simple model is motivated by the multi-lepton anomalies and excesses in di-photon, $$Z\gamma $$ Z γ , and WW spectra at $$\approx 152$$ ≈ 152 GeV. The model contains, in addition to the SM particle content, a CP -even neutral Higgs ( $$\varDelta ^0$$ Δ 0 ) and a charged state ( $$\varDelta ^\pm $$ Δ ± ), which are quasi-degenerate in mass. Observing the charged scalar at the LHC and measuring its mass is very challenging, since it dominantly decays to WZ , tb , and $$\tau \nu $$ τ ν . In this article, we consider the discovery prospects of the charged Higgs with mass 150 GeV at future electron-positron colliders. Taking into account $$e^+e^- \rightarrow \gamma ^*,Z^* \rightarrow \varDelta ^\pm \varDelta ^\mp $$ e + e - → γ ∗ , Z ∗ → Δ ± Δ ∓ as the production mechanism and the dominant decay modes, we define three signal regions (SR) to study the 150 GeV charged Higgs properties: SR1: $$\ge 3j + 1\ell $$ ≥ 3 j + 1 ℓ , SR2: $$\ge 3\ell + \tau _{\text {had}}$$ ≥ 3 ℓ + τ had , SR3: $$\ge 4j + \tau _{\text {had}}$$ ≥ 4 j + τ had . For $$m_{\varDelta ^\pm }=150\,\text {GeV}$$ m Δ ± = 150 GeV , a