$\mu \to e\gamma$ Search with Polarized Muons

Abstract

A search for the lepton-flavor violating ${\mu }^{+}\to e^{+}\gamma$ decay using polarized muons is proposed. By measuring the angular distribution of $e^{+}$s with respect to the muon spin direction, in particular antiparallel $e^{+}$s, the serious physics background from ${\mu }^{+}\to e^{+}\nu \overline{\nu }\gamma$ as well as accidental background from normal muon decay accompanied by a high-energy photon can be suppressed significantly. In addition to the enhancement of the sensitivity, the angular distribution would discriminate among different extensions to the Standard Model, once the signal is observed.

Comments: 11 pages, 2 figures, also available via anonymous ftp at ftp://ftp.kek.jp/kek/preprints/TH/TH-478