Minimal cascade decay of the top quark through a new scalar

Abstract

We explore a possible decay of the top quark into a new scalar $ϕ_t$ plus a charm quark. The decay is mediated by a dimension-5 operator that may be generated by the exchange of a heavy vectorlike quark, $χ$, and can have a branching fraction close to a percent. In a minimal model, $ϕ_t$ decays due to the same operator that allows the nonstandard top decay, leading to a final state involving a $c$ jet, a $b$ jet and a $W$ boson. Hence, the top quark would undergo a nonstandard cascade decay through $ϕ_t$ and then through an off-shell top quark. The main nonstandard collider signal is a $t \bar t \to c \, \bar c \, b \, \bar b \, W^+ W^-$ process. In addition, production of the vectorlike quark at the LHC would lead to a signal of the type $χϕ_t \, j \to 3c + b \, \bar b \, W W j$.