Single Top Production in $e^+ e^-$, $e^- e^-$, $γe$ and $γγ$ Collisions

Abstract

Single top quark cross section evaluations for the complete sets of tree-level diagrams in the $e^+ e^-$, $e^- e^-$, $γe$ and $γγ$ modes of the next linear collider with unpolarized and polarized beams are performed within the Standard Model and beyond. From comparison of all possibilities we conclude that the process $γ_+ e^-_L \to e^- t \bar b$ is extremely favoured due to large cross section, no $t \bar t$ background, high degrees of beam polarization, and exceptional sensitivities to $V_{tb}$ and anomalous $Wtb$ couplings. Similar reasons favour the process $e^- e^- \to e^- ν_e \bar t b$ for probing top quark properties despite a considerably lower cross section. Less favourable are processes like $e^+ e^-, γγ\to e^- ν_e t \bar b$. Three processes were chosen to probe their sensitivity to anomalous $Wtb$ couplings, with best bounds found for $γ_+ e^-_L \to e^- t \bar b$ and $e^+_R e^-_R \to e^- ν_e t \bar b$.