Detection of heavy charged Higgs bosonsin $e^ + e^-\to t\bar b H^-$ production at future Linear Colliders

Abstract

Heavy charged Higgs bosons ( $H^\pm$ ) of a Type II 2-Higgs doublet model (2HDM) can be detected at future electron-positron Linear Colliders (LCs) even when their mass is larger than half the collider energy. The single Higgs mode $e^ + e^-\to t\bar b H^- + {\mathrm {c.c.}} \to 4b + {\mathrm {j}}{\mathrm {j}} + \ell + p_{\mathrm {T}}^{\mathrm {miss}}$ (where j represents a jet and with $\ell = e,\mu$ ) contributes to extend the discovery reach of $H^\pm$ states into the mass region $M_{H^\pm}\gtrsim \sqrt s/2$ , where the well studied pair production channel $e^ + e^-\to H^-H^ + $ is no longer available. With a technique that allows one to reconstruct the neutrino four-momentum in the decay $t\to b W^ + \to b \ell^ + \nu$ , one can suppress the initially overwhelming main irreducible background due to $e^ + e^-\to t\bar t b\bar b$ (via a gluon splitting into $b\bar b$ pairs) to a negligible level. However, for currently foreseen luminosities, one can establish a statistically significant $H^\pm$ signal only over a rather limited mass region, of 20 GeV or so, beyond $M_{H^\pm}\approx \sqrt s/2$ , for very large or very small values of $\tan\beta$ and provided high b-tagging efficiency can be achieved.