Measurement of the radiative decay of polarized muons in the MEG experiment

We studied the radiative muon decay (Formula presented.) by using for the first time an almost fully polarized muon source. We identified a large sample ((Formula presented.) 13,000) of these decays in a total sample of (Formula presented.) positive muon decays collected in the MEG experiment in the years 2009–2010 and measured the branching ratio (Formula presented.) for (Formula presented.) and (Formula presented.) , consistent with the Standard Model prediction. The precise measurement of this decay mode provides a basic tool for the timing calibration, a normalization channel, and a strong quality check of the complete MEG experiment in the search for (Formula presented.) process.