Probing the pair production of first-generation vector-like leptons at future $e^+e^-$ colliders

TL;DR

This work addresses the discovery potential for the first-generation weak-isosinglet Vector-Like Lepton $E^{\pm}$ at future $e^+e^-$ colliders by studying pair production and decays mediated through a small mixing with the SM electron. The authors compute polarized pair-production cross sections, implement a minimal singlet VLL model with $\epsilon$-controlled mixing, and analyze two multilepton final states, $2\ell+2j+\slashed{E}_T$ and $3\ell+2j+\slashed{E}_T$, using full MC simulations and detector emulations for ILC/CLIC-like setups. They demonstrate that optimized kinematic cuts and beam polarization greatly suppress SM backgrounds, yielding 2$\sigma$ exclusion and 5$\sigma$ discovery reach up to $m_E \sim$ $490$, $740$, and $1440$ GeV at $\sqrt{s} = 1$, 1.5, and 3 TeV with appropriate integrated luminosities, surpassing current LHC constraints. The results underscore the strong potential of future $e^+e^-$ colliders to probe heavy singlet VLLs beyond current hadron-collider limits and to provide complementary verification via a second dataset (3-lepton channel) for confirmation, with significance tied to collider energy and luminosity through the standard likelihood formalism.

Abstract

This work explores the discovery potential of the first-generation weak isosinglet Vector-Like Leptons (VLLs), denoted by $E^\pm$, via pair production at future electron-positron colliders. Our analysis adopts a comprehensive framework that incorporates beam polarization configurations and leverages detailed detector simulations. We focus on two distinct multilepton signatures: the $2\ell + 2j + \slashed{E}_T$ and $3\ell + 2j + \slashed{E}_T$ final states ($\ell = e, μ$). Both signatures arise from the decay $E^{\pm} \to Z e^{\pm} / W^{\pm} ν_\ell$ and are distinguished by the decay patterns of the associated gauge bosons. By applying optimized selection criteria to both signal and background events, we establish exclusion sensitivities and discovery prospects across the VLL mass spectrum. Our findings demonstrate that, for integrated luminosities of $\SI{25}{fb^{-1}}$, $\SI{90}{fb^{-1}}$ and $\SI{1000}{fb^{-1}}$ at corresponding center-of-mass (c.m.) energies of $\SI{1}{TeV}$, $\SI{1.5}{TeV}$ and $\SI{3}{TeV}$, the accessible mass range extends to approximately $\SI{490}{GeV}$, $\SI{740}{GeV}$ and $\SI{1440}{GeV}$, which represents a substantially improvement over the detection limits of existing hadron collider experiments.

Figures (9)

• Figure 1: Production cross sections for $e^{+}e^{-}\to E^{+}E^{-}$ as a function of $m_{E}$ at $\sqrt{s} = 1$ TeV, 1.5 TeV and 3 TeV, using the beam polarization configuration $(P_{e^+}, P_{e^-}) = (-0.2, 0.8)$.
• Figure 2: Characteristic Feynman diagrams illustrating the signal processes for Cases 1 (left) and 2 (right) discussed in the text.
• Figure 3: Comparison of normalized distributions between signal processes and relevant SM backgrounds at $\sqrt{s} = 1$ TeV for Case 1.
• Figure 4: Same as Figure \ref{['fig:distribution1-1']}, but for $\sqrt{s} = 1.5$ TeV.
• Figure 5: Same as Figure \ref{['fig:distribution1-1']}, but for $\sqrt{s} = 3$ TeV.