Probing first-generation doublet vector-like leptons via single production at the 3 TeV CLIC

Abstract

The single production of first-generation $\mathrm{SU}(2)_L$ doublet vector-like leptons (VLLs) at the Compact Linear Collider (CLIC) with $\sqrt{s}=3~\mathrm{TeV}$ is studied. The neutral and charged VLL states are investigated through $e^+e^-\rightarrowν_e\bar N+\barν_eN$ and $e^+e^-\rightarrow e^\pm E^\mp$, respectively. The neutral VLL is searched for in the $N\rightarrow W^\mp e^\pm$ channel with $W^\pm\rightarrow jj$, leading to the $e^\pm+2j+\slashed{E}_T$ final state. The charged VLL is explored through $E^\pm\rightarrow e^\pm h$ ($h\rightarrow b\bar b$) and $E^\pm\rightarrow e^\pm Z$ ($Z\rightarrow q\bar q$), yielding the $e^+e^-+2b$ and $e^+e^-+2j$ signatures. Signal and background simulations include initial-state radiation, beamstrahlung, and detector effects. Cut-based analyses are performed for integrated luminosities of $1$, $3$, and $5~\mathrm{ab}^{-1}$ to obtain the exclusion and discovery sensitivities in the VLL mass--mixing parameter space. The neutral-VLL channel gives the best sensitivity. At $1~\mathrm{ab}^{-1}$, the $2σ$ exclusion reaches $\varepsilon\simeq0.013$ at $M_N=1.3~\mathrm{TeV}$ and $\varepsilon\simeq0.065$ at $M_N=2.9~\mathrm{TeV}$, while the $5σ$ discovery reach corresponds to $\varepsilon\simeq0.02$--$0.10$. At $5~\mathrm{ab}^{-1}$, the charged-VLL channels probe masses up to about $2.9~\mathrm{TeV}$ and $2.8~\mathrm{TeV}$ in the $e^\pm h$ and $e^\pm Z$ modes, respectively. These results demonstrate that a 3 TeV CLIC can provide sensitive probes of first-generation doublet VLLs over a wide mass range, including scenarios with small VLL--electron mixing.