New physics in multi-electron muon decays

Abstract

Abstract We study the exotic muon decays with five charged tracks in the final state. First, we investigate the Standard Model rate for μ + → 3e + 2e − 2ν ( B $$ \mathcal{B} $$ = 4.0 × 10 −10) and find that the Mu3e experiment should have tens to hundreds of signal events per 1015 μ + decays, depending on the signal selection strategy. We then turn to a neutrinoless μ + → 3e + 2e − decay that may arise in new-physics models with lepton-flavor-violating effective operators involving a dark Higgs h d . Following its production in μ + → e + h d decays, the dark Higgs can undergo a decay cascade to two e + e − pairs through two dark photons, h d → γ d γ d → 2(e + e − ). We show that a μ + → 3e + 2e − search at the Mu3e experiment, with potential sensitivity to the branching ratio at the O $$ \mathcal{O} $$ (10 −12) level or below, can explore new regions of parameter space and new physics scales as high as Λ ∼ 1015 GeV.

Keywords

• Lepton Flavour Violation (charged)
• New Light Particles
• Rare Decays