Abstract
Abstract We revisit the potential of a Linear Collider concerning the study of lepton flavour violation, in view of new LHC bounds and of the (very) recent developments in lepton physics. Working in the framework of a type I supersymmetric seesaw, we evaluate the prospects of observing seesaw-induced lepton flavour violating final states of the type eμ plus missing energy, arising from e + e − and e − e − collisions. In both cases we address the potential background from standard model and supersymmetric charged currents. We also explore the possibility of electron and positron beam polarisation. The statistical significance of the signal, even in the absence of kinematical and/or detector cuts, renders the observation of such flavour violating events feasible over large regions of the parameter space. We further consider the μ − μ − + $ E_{{^{\text{miss}}}}^T $ final state in the e − e − beam option finding that, due to a very suppressed background, this process turns out to be a truly clear probe of a supersymmetric seesaw, assuming the latter to be the unique source of lepton flavour violation.
Highlights
Large array of charged lepton flavour violation observables might provide a unique probe of this mass generation mechanism
Following recent developments in lepton physics and the new physics searches at the LHC, we have revisited the potential of a Linear Collider concerning the study of lepton flavour violation: in particular, we investigated charged lepton flavour violation (cLFV) in e+e− and e−e− collisions in the framework of a type I SUSY seesaw
Due to the leptonic mixing associated with charged current interactions (UMNS), cLFV will always occur in any model that can accommodate neutrino oscillations, independently from any mechanism of mass generation or new physics model
Summary
Irrespective of the Dirac/Majorana nature of the neutrinos, and of the underlying mechanism of ν-mass generation, charged lepton currents (i.e., W ± li νj) do violate lepton flavour, with a strength given by the relevant entry of the UMNS leptonic mixing matrix, Uij. The possibility of electron and positron beam polarisation is instrumental in disentangling the above processes [64, 65]: in the ideal case of 100% polarised e+ and e− beams, that is an LL polarisation of (Pe−, Pe+) = (−100%, −100%), and with the exception of the W -strahlung processes, the other SM contributions (C) would vanish, as well as most of those arising from pure SUSY LFV charged currents (B) Under this “ideal” beam configuration, and via some kinematical cuts, a cLFV signal (A) would clearly point towards flavour mixing in the slepton sector (for instance due to a SUSY seesaw), manifest in neutral currents. In addition to probing cLFV in neutral currents in a remarkably clean way, this channel allows to fully benefit from the LC muon detector efficiency
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