Limits on vectorlike leptons from searches for anomalous production of multi-lepton events

Abstract

We consider extensions of the Standard Model by vectorlike leptons and set limits on a new charged lepton, e ± 4 , using the ATLAS search for anomalous production of multi-lepton events. It is assumed that only one Standard Model lepton, namely the muon, dominantly mixes with vectorlike leptons resulting in possible decays e ± 4 → W ± ν µ , e ± 4 → Zµ ± , and e ± 4 → hµ ± . We derive generally applicable limits on the new lepton treating the branching ratios for these processes as free variables. We further interpret the general limits in two scenarios with e ± 4 originating predominantly from either the SU(2) doublet or the SU(2) singlet. The doublet case is more constrained as a result of larger production cross-section and extra production processes e ± 4 ν 4 and ν 4 ν 4 in addition to e + 4 e − 4 , where ν 4 is a new neutral state accompanying e 4 . We find that some combinations of branching ratios are poorly constrained, whereas some are constrained up to masses of more than 500 GeV. In the doublet case, assuming BR(ν 4 → W µ) = 1, all masses below about 300 GeV are ruled out. Even if this condition is relaxed and additional decay modes, ν 4 → Zν µ and ν 4 → hν µ , are allowed, below the Higgs threshold still almost all of the parameter space (of independent branching ratios) is ruled out. Nevertheless, even assuming the maximal production cross-section, which coincides with the doublet case, the new charged lepton can still be as light as the LEP-II limit allows. We discuss several possible improvements of current experimental analyses that would dramatically reduce the allowed parameter space, even with current data.

Complete vectorlike fourth family with U(1)′ : A global analysis

“…The final states in Eq. (4.6) have been studied as a signature of VL leptons in several papers [115][116][117][118][119][120][121]. However, there is no study by LHC experiments of VL leptons decaying to a muon based on LHC Run-2 data.…”

Contributions of flavor violating couplings of a Higgs boson to pp → W W

“…These include constraints from electroweak precision data and from pair production of new leptons from searches for anomalous production of multi lepton events, discussed in ref. [28]. We will discuss an explicit scenario along these lines in a forthcoming publication [23].…”

“…For example constraints on pair production of new leptons from searches for anomalous production of multi lepton events, discussed in ref. [28], highly depend on the SU(2) doublet component in the mass eigenstate ν 4 and on the mass of extra charged lepton. The results presented in this paper do not depend on these further assumptions.…”

Vectorlike leptons: Muon g−2 anomaly, lepton flavor violation, Higgs boson decays, and lepton nonuniversality

“…There are more recent bounds on the mass of VL leptons obtained from reinterpreting ATLAS and CMS experiments [12][13][14][15]. If the lightest VL lepton is predominantly E L,R , then the bound is similar to the LEP bound.…”