Charged Lepton Flavour Violation using Intense Muon Beams at Future Facilities

Abstract

A submission to the 2020 update of the European Strategy for Particle Physics on behalf of the COMET, MEG, Mu2e and Mu3e collaborations. AbstractCharged-lepton flavour-violating (cLFV) processes offer deep probes for new physics with discovery sensitivity to a broad array of new physics models -SUSY, Higgs Doublets, Extra Dimensions, and, particularly, models explaining the neutrino mass hierarchy and the matterantimatter asymmetry of the universe via leptogenesis. The most sensitive probes of cLFV utilize high-intensity muon beams to search for µ → e transitions.We summarize the status of muon-cLFV experiments currently under construction at PSI, Fermilab, and J-PARC. These experiments offer sensitivity to effective new physics mass scales approaching O(10 4 ) TeV/c 2 . Further improvements are possible and next-generation experiments, using upgraded accelerator facilities at PSI, Fermilab, and J-PARC, could begin data taking within the next decade. In the case of discoveries at the LHC, they could distinguish among alternative models; even in the absence of direct discoveries, they could establish new physics. These experiments both complement and extend the searches at the LHC.Contact: André Schöning [schoning@physi.uni-heidelberg.de] arXiv:1812.06540v1 [hep-ex] Executive Summary• Charged-lepton flavour-violating (cLFV) processes provide an unique discovery potential for physics beyond the Standard Model (BSM). These cLFV processes explore new physics parameter space in a manner complementary to the collider, dark matter, dark energy, and neutrino physics programmes.

A little theory of everything, with heavy neutral leptons

“…For example the Mu3e experiment may eventually probe µ → 3e down to the level of 10 −16 branching ratio [61]. Moreover the process of µN → eN conversion in nuclei is expected to yield interesting limits in upcoming experiments, including Mu2e [62] at Fermilab and COMET [63] at KEK.…”

A Search for Charged Lepton Flavor Violation in the Mu2e Experiment

“…Mu2e is expected to further increase sensitivity by another two orders of magnitude beyond these measurements, culminating an intense program over the next years that may well yield the first discovery of CLFV events. The planned timeline of this experimental program is From Baldini et al 47 shown in Figure 14. If a signal is observed then the complementarity between the three muon transition modes will be a powerful discriminant among the underlying New Physics models.…”

A search for charged lepton flavor violation in the Mu2e experiment

“…The current best limits for each process are shown on the left in parentheses, while expected future sensitivities are indicated by order of magnitude along the bottom of each row. From Baldini et al47…”