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 → Wμ) = 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.
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Dermíšek, R., Hall, J.P., Lunghi, E. et al. Limits on vectorlike leptons from searches for anomalous production of multi-lepton events. J. High Energ. Phys. 2014, 13 (2014). https://doi.org/10.1007/JHEP12(2014)013
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DOI: https://doi.org/10.1007/JHEP12(2014)013