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

The single production of first-generation $\mathrm{S}\mathrm{U}(2{)}_L$ doublet vector-like leptons (VLLs) at the Compact Linear Collider (CLIC) with $\sqrt{s}=3\mathrm{T}\mathrm{e}\mathrm{V}$ is studied. The neutral and charged VLL states are investigated through $e^{+}{e}^{-}\to {\nu }_e\bar{N}+{\bar{\nu }}_{e}N$ and $e^{+}{e}^{-}\to e^{\pm }{E}^{\mp }$, respectively. The neutral VLL is searched for in the $N\to W^{\mp }{e}^{\pm }$ channel with $W^{\pm }\to jj$, leading to the $e^{\pm }+2j+\text{slashed}{E}_T$ final state. The charged VLL is explored through $E^{\pm }\to e^{\pm }h$ ($h\to b\bar{b}$) and $E^{\pm }\to e^{\pm }Z$ ($Z\to q\bar{q}$), 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 $5{\mathrm{a}\mathrm{b}}^{-1}$ to obtain the exclusion and discovery sensitivities in the VLL mass–mixing parameter space. The neutral-VLL channel gives the best sensitivity. At $1{\mathrm{a}\mathrm{b}}^{-1}$, the $2\sigma$ exclusion reaches $\epsilon \simeq 0.013$ at $M_N=1.3\mathrm{T}\mathrm{e}\mathrm{V}$ and $\epsilon \simeq 0.065$ at $M_N=2.9\mathrm{T}\mathrm{e}\mathrm{V}$, while the $5\sigma$ discovery reach corresponds to $\epsilon \simeq 0.02$–$0.10$. At $5{\mathrm{a}\mathrm{b}}^{-1}$, the charged-VLL channels probe masses up to about $2.9\mathrm{T}\mathrm{e}\mathrm{V}$ and $2.8\mathrm{T}\mathrm{e}\mathrm{V}$ 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.