A limit for the μ→eγμ→eγ decay from the MEG experiment

Adam, J.; Bai, X.; Baldini, A.; Baracchini, E.; Barchiesi, A.; Bemporad, C.; Boca, G.; Cattaneo, P. W.; Cavoto, G.; Cecchet, G.; Cei, F.; Cerri, C.; De Bari, A.; De Gerone, M.; Dokep, T.; Dussoni, Simeone; Egger, J.; Galli, L.; Gallucci, G.; Gatti, Flavio; Goldenl, B.; Grassi, M.; Grigoriev, D. N.; Haruyama, T.; Hildebrandt, M.; Hisamatsu, Y.; Ignatov, F.; Iwamoto, T.; Kaneko, D.; Kettle, P. R.; Khazin, B. I.; Kiselevn, O.; Korenchenko, A.; Kravchuk, N.; Maki, A.; Mihara, S.; Molzon, W.; Mori, T.; Mzavin, D.; Natori, H.; Nardò, R.; Nicolò, D.; Nishiguchi, H.; Nishimura, Y.; Ootani, W.; Panareo, M.; Papa, A.; Pazzi, R.; Piredda, G.; Popov, A.; Renga, F.; Ritt, S.; Rossella, M.; Sawada, R.; Schneebeli, M.; Sergiampietri, F.; Signorelli, G.; Suzuki, S.; Topchyan, C.; Tumakov, V.; Uchiyama, Y.; Valle, Riccardo; Voena, C.; Xiao, F.; Yamadam, S.; Yamamotom, A.; Yamashita, S.; Yudin, Y. u. V.; Zanello, D.

doi:10.1016/j.nuclphysb.2010.03.030

A search for the decay μ+→e+γ, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(μ+→e+γ)⩽2.8×10−11 (90% C.L.). This corresponds to the measurement of positrons and photons from ∼1014 stopped μ+-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.