Searching for vector-like leptons decaying into an electron and missing transverse energy in e$^{+}$e$^{-}$ collisions with $\sqrt{s} = 240$ GeV at the FCC-ee

Abstract

This analysis delves into the lepton portal dark matter by utilizing Monte Carlo simulated samples from electron-positron collisions at the Future Circular Collider (FCC-ee), operating at a center of mass energy of 240 GeV and an integrated luminosity of 10.8 ab$^{-1}$. The study explores a specific benchmark scenario in which dark matter is represented as a scalar particle produced as a byproduct of a vector-like lepton. The key signal signature features missing transverse energy alongside dilepton events. Should new physics not be detected, this study establishes 95\% confidence level exclusion limits on the mass of the vector-like leptons and the Yukawa coupling.

Figures (8)

• Figure 1: Feynman diagrams of the vector-like lepton pair production for \ref{['fey1']} s-channel and \ref{['fey2']} t-channel processes, followed by the decay to the dark matter.
• Figure 2: Dependence of cross sections for the signal process $e^{+} e^{-} \rightarrow L\tilde{L} \rightarrow e^{+}e^{-} \chi\chi$, induced by the VLL model, on the VLL mass with $\sqrt{s}$ = 240 GeV for different values of $\lambda_{L}$ and $\Delta M = 5$ GeV.
• Figure 3: The measured missing transverse energy ($E_{T}^{miss}$) spectrum, after applying pre-selection summarized in table \ref{['cuts']}, for the estimated SM backgrounds and different choices of VLL masses generated based on the VLL model, with $\lambda_{L} = 1.0$ and $\Delta M = 5$ GeV in \ref{['met1:5gev']}, and 10 GeV in \ref{['met1:10gev']}.
• Figure 4: The distributions of three variables for dielectron events, where each electron passes the low $p_T$ electron ID discussed in the pre-selection in table \ref{['cuts']}. The four variables are $|p_{T}^{e^{+}e^{-}} - E_{T}^{miss}|/p_{T}^{e^{+}e^{-}}$\ref{['figure:ptdiff']}, $\Delta R(e^{+}e^{-})$\ref{['figure:deltar']}, and $\text{cos}(\text{Angle}_{3D})$\ref{['figure:3Dangle']}. The model corresponds to the VLL with different values of $M_{L} = 50$ GeV and $M_{\chi} = 45$ GeV, and for the SM backgrounds. The vertical dashed lines correspond to the chosen cut value for each variable.
• Figure 5: Distributions of the N-1 efficiencies plotted against the transverse momentum of the leading reconstructed electron ($p^{e}_{T}$) for the following cuts; $|p_{T}^{e^{+}e^{-}} - E_{T}^{miss}|/p_{T}^{e^{+}e^{-}} < 0.1$\ref{['eff2']}, $\Delta R(e^{+}e^{-}) < 3.0$\ref{['eff4']}, and $\text{cos}(\text{Angle}_{3D}) < -0.9$\ref{['eff5']} for the signal in the VLL model with $\Delta M = 5$ GeV and for the SM backgrounds.