Abstract
We show that dark photons (A ′) with masses ∼ 10-80 MeV can be probed in the decay $$ {\mu}^{+}\to {e}^{+}{\nu}_e{\overline{\nu}}_{\mu }A^{\prime } $$ , A ′ → e + e −, with the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) in Switzerland. With an expected 1015 (5.5 × 1016) muon decays in 2015–2016 (2018 and beyond), Mu3e has the exciting opportunity to probe a substantial fraction of currently unexplored dark photon parameter space, probing kinetic-mixing parameter, ϵ, as low as ϵ 2 ∼ 10−7 (10−8). No modifications of the existing Mu3e setup are required.
Highlights
Νμ νμ νμ the SM photon leads to an -suppressed coupling of the dark photon to the electromagnetic current, JEμM, i.e., to quarks and charged leptons
We show that dark photons (A ) with masses ∼ 10–80 MeV can be probed in the decay μ+ → e+νeνμA, A → e+e−, with the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) in Switzerland
With an expected 1015 (5.5 × 1016) muon decays in 2015–2016 (2018 and beyond), Mu3e has the exciting opportunity to probe a substantial fraction of currently unexplored dark photon parameter space, probing kineticmixing parameter, as low as 2 ∼ 10−7 (10−8)
Summary
The Mu3e experiment at PSI [51] has been proposed to search for the charged lepton flavor violating decay μ+ → e+e−e+ with an ultimate sensitivity of 10−16, four orders below the current limits. It will take advantage of one of the most intense sources of muons in the world. The production mechanism is illustrated in figure 1: the dark photon can be either emitted from the initial state radiation off the μ+, or final state radiation off the e+, or radiate off the internal W -boson. Since the backgrounds are expected to be greatly reduced with respect to prompt decays, displaced vertices could provide sensitivity to low values of the kinematic mixing
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