Experimental Results on the Radiativeπ−μDecay

A total of 93 045 $\pi -\mu -e$ decays have been examined in Ilford G-5 plates, where both the $\pi$ meson and the $\mu$-meson decays take place in the emulsion, in order to study the $\pi \to \mu +\nu +\gamma$ decay. From the total number of short muon tracks thus found, all cases possibly due to pion decays in flight were eliminated. Accurate corrections were carried out taking into account the straggling effects on the normal muons, so as to establish a safe upper limit in the anomalous muon range determination. After carefully correcting for the geometrical losses and experimental biases, the value (1.24±0.25)×${10}^{-4\mathrm{}}$ was obtained for the probability of a pion decaying into a muon whose track is shorter than 435 μ. This result is in fair agreement with the theoretical predictions on the pion radiative decay.