Search for single production of vector-like quarks decaying into final states with a Z boson and a top or a bottom quark

A search for the single production of vector-like quarks, $T$ and $B$, decaying into a Z boson and a top or a bottom quark respectively, is presented using data collected by the CMS experiment in proton-proton collisions at $\sqrt s=13~\mathrm{TeV}$. An additional exotic production mode is studied for the $T$ quark, i.e. the production of a heavy resonance $Z^{\prime}$ with its subsequent decay into $Tt$. The search has been performed in events with a Z boson decaying leptonically, accompanied by a bottom or a top quark decaying hadronically. Observed production cross sections for $T$ and $B$ in the range between $0.97$ and $0.13~\mathrm{pb}$ are excluded at $95\%$ confidence level, depending on the resonance mass that ranges from $0.7$ to $1.7~\mathrm{TeV}$, while observed production cross sections for $Z^{\prime}$ are excluded in the range between $0.31$ and $0.14~\mathrm{pb}$, in a mass range between $1.5$ and $2.5~\mathrm{TeV}$.