Multi-lepton signatures of vector-like leptons with flavor

TL;DR

This paper explores collider signatures of vector-like leptons with flavor, proposing new observables for detecting their signals at the LHC, especially in models explaining muon and electron magnetic moments.

Contribution

It introduces novel multi-lepton observables based on flavor-violating scalar decays to identify vector-like leptons at the LHC.

Findings

Vector-like leptons below 300 GeV (singlets) are excluded by current data.

Doublet vector-like leptons below 800 GeV are also excluded.

New flavor-violating observables can help discover and analyze these particles in future collider runs.

Abstract

We investigate collider signatures of standard model extensions featuring vector-like leptons and a flavorful scalar sector. Such a framework arises naturally within asymptotically safe model building, which tames the UV behavior of the standard model towards the Planck scale and beyond. We focus on values of Yukawa couplings and masses which allow to explain the present data on the muon and electron anomalous magnetic moments. Using a CMS search based on $77.4 \, \rm{fb}^{-1}$ at the $\sqrt{s}=13$ TeV LHC we find that flavorful vector-like leptons are excluded for masses below around $300$ GeV if they are singlets under $SU(2)_L$, and around $800$ GeV if they are doublets. Exploiting the flavor-violating-like decays of the scalars, we design novel null test observables based on opposite sign opposite flavor invariant masses. These multi-lepton distributions allow to signal new physics and to extract mass hierarchies in reach of near-future searches at the LHC and the HL-LHC.