Publication Date:
2020-09-01
Description:
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, $$upmu ^+
ightarrow mathrm {e}^+mathrm {X}, mathrm {X}
ightarrow upgamma upgamma $$ μ + → e + X , X → γ γ . This search uses a dataset resulting from $$7.5imes 10^{14}$$ 7.5 × 10 14 stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c$$^2$$ 2 for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c$$^2$$ 2 , down to $${mathcal {O}}(10^{-11})$$ O ( 10 - 11 ) at 90% confidence level.
Print ISSN:
1434-6044
Electronic ISSN:
1434-6052
Topics:
Physics
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