Improved search for two body muon decay $\hat{I}{¼}^{+}\to e^{+}{X}_H$

Abstract

Charged lepton flavor violating muon decay $\hat{I}{¼}^{+}\to e^{+}{X}_H$, where $X_H$ is a massive neutral boson, was sought by searching for extra peaks in the muon decay $\hat{I}{¼}^{+}\to e^{+}\hat{I}½\bar{\hat{I}}½$ energy spectrum in the $m_{X_H}$ mass region $47.8-95.1$ MeV/$c^2$. No signal was found and 90% confidence level upper limits were set on the branching ratio $\hat{I}“(\hat{I}{¼}^{+}\to e^{+}{X}_H)/\hat{I}“(\hat{I}{¼}^{+}\to e^{+}\hat{I}½\bar{\hat{I}}½)$ at the level of $10^{-5}$ for this region.

3 pages, 2 figures