Search for rare muon decays with the Crystal Box detector

Abstract

A search with the Crystal Box detector shows no evidence for the lepton-family-number-nonconserving decays \ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}, \ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma}, or \ensuremath{\mu}\ensuremath{\rightarrow}eee. The search provides upper limits for the branching ratios of \ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})/\ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}evv\ifmmode\bar\else\textasciimacron\fi{})4.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ (90% C.L.), \ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma})/\ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}evv\ifmmode\bar\else\textasciimacron\fi{})7.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ (90% C.L.), and \ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}eee)/\ensuremath{\Gamma}(\ensuremath{\mu}\ensuremath{\rightarrow}evv\ifmmode\bar\else\textasciimacron\fi{})3.${510}^{\mathrm{\ensuremath{-}}11}$ (90% C.L.). In addition, a limit for the emission of a light scalar or pseudoscalar boson in radiative muon decay is given.