Search for. mu. /sup +/. -->. e/sup +/. gamma

TLDR: In this article, a kinematically complete search for the muon decay was performed using a magnetic spectrometer outfitted with proportional chambers to measure the positron momentum vector and a large segmented NaI(Tl) array to determine the gamma-ray energy and impact point.

Abstract: This paper describes a kinematically complete search for the muon decay ..mu../sup +/..-->..e/sup +/..gamma... The experiment used a magnetic spectrometer outfitted with proportional chambers to measure the positron momentum vector and a large segmented NaI(Tl) array to determine the ..gamma..-ray energy and impact point. The positrons were mostly from normal muon decay while the ..gamma.. rays were mostly from internal and external bremsstrahlung. Approximately 3 x 10/sup 12/ muons were stopped in a 50-mg/cm/sup 2/ polyethylene target. The relative timing between the positron and the ..gamma.. ray was measured with a resolution of 1.9 ns full width at half maximum (FWHM) by the use of a plastic-scintillator hodoscope for the positron and by NaI(Tl) constant-fraction timing for the ..gamma.. ray. The positron energy resolution averaged over all data was 8.8% FWHM, and the ..gamma..-ray energy resolution was 8% FWHM, both at 52.8 MeV. When the ..gamma.. ray is assumed to originate at the same place in the target as the positron, the rms error in the measurement of the angle between the positron and ..gamma..-ray momentum vectors was 37 mrad. The acceptance of the apparatus for ..mu../sup +/..-->..e/sup +/..gamma.. events was (1.75 +- 0.04)%. A maximum-likelihood analysis established a 90%-confidencemore » upper limit for the branching ratio GAMMA(..mu../sup +/..-->..e/sup +/..gamma..)/GAMMA(..mu../sup +/..-->..e..nu nu..) of 1.7 x 10/sup -10/.« less