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

作者：Dermisek Radovan^*; Hall Jonathan P; Lunghi Enrico; Shin Seodong

来源：The Journal of High Energy Physics, 2014, 2014(12): 013.

DOI：10.1007/JHEP12(2014)013

• Phenomenological Models
• Hadronic Colliders

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-+/-nu(mu), e(4)(+/-) -> Z mu(+/-), and e(4)(+/-) -> h mu(+/-). 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)(+/-)nu 4 and nu 4 nu 4 in addition to e(4)(+)e(4)(-) where v(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(nu(4) -> W mu) = 1, all masses below about 300 GeV are ruled out. Even if this condition is relaxed and additional decay modes, nu(4) -> Z nu(mu) and nu(4) -> h nu(mu), 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.

• 出版日期2014-12-2