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

The MEG Collaboration, Null; Baldini, A. M.; Bao, Y.; Baracchini, E.; Bemporad, Carlo; Berg, F.; Biasotti, M.; Boca, G.; Cattaneo, P. W.; Cavoto, G.; Cei, Fabrizio; Chiarello, G.; Chiri, C.; de Bari, A.; De Gerone, M.; D’Onofrio, A.; Dussoni, Simeone; Fujii, Y.; Galli, Luca; Gatti, F.; Grancagnolo, F.; Grassi, M.; Graziosi, A.; Grigoriev, D. N.; Haruyama, T.; Hildebrandt, M.; Hodge, Z.; Ieki, K.; Ignatov, F.; Iwamoto, T.; Kaneko, D.; Kang, Tae Im; Kettle, P. R.; Khazin, B. I.; Khomutov, N.; Korenchenko, A.; Kravchuk, N.; Lim, G. M. A.; Mihara, S.; Molzon, W.; Mori, Toshinori; Mtchedlishvili, A.; Nakaura, S.; Nicolo', Donato; Nishiguchi, H.; Nishimura, M.; Ogawa, S.; Ootani, W.; Panareo, M.; Papa, A.; Pepino, A.; Piredda, G.; Pizzigoni, G.; Popov, A.; Renga, F.; Ripiccini, E.; Ritt, S.; Rossella, M.; Rutar, G.; Sawada, R.; Sergiampietri, F.; Signorelli, Giovanni; Tassielli, G. F.; Tenchini, Francesco; Uchiyama, Y; Venturini, Marco; Voena, C.; Yamamoto, A.; Yoshida, K.; You, Z.; Yudin, Y. u. V.

doi:10.1140/epjc/s10052-016-3947-6

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.