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Baldini, A. M.; Berg, F.; Biasotti, M.; Boca, G.; Cattaneo, P. W.; Cavoto, G.; Cei, F.; Chiappini, M.; Chiarello, G.; Chiri, C.; Corvaglia, A.; de Bari, A.; De Gerone, M.; Francesconi, M.; Galli, L.; Gatti, F.; Grancagnolo, F.; Grassi, M.; Grigoriev, D. N.; Hildebrandt, M.; Hodge, Z.; Ieki, K.; Ignatov, F.; Iwai, R.; Iwamoto, T.; Kobayashi, S.; Kettle, P.-R.; Kyle, W.; Khomutov, N.; Kolesnikov, A.; Kravchuk, N.; Kuchinskiy, N.; Libeiro, T.; Lim, G. M. A.; Malyshev, V.; Matsuzawa, N.; Meucci, M.; Mihara, S.; Molzon, W.; Mori, Toshinori; Mtchedilishvili, A.; Nakao, M.; Natori, H.; Nicolò, D.; Nishiguchi, H.; Nishimura, M.; Ogawa, S.; Onda, R.; Ootani, W.; Oya, A.; Palo, D.; Panareo, M.; Papa, A.; Pettinacci, V.; Pizzigoni, G.; Popov, A.; Renga, F.; Ritt, S.; Rozhdestvensky, A.; Rossella, M.; Sawada, R.; Schwendimann, P.; Signorelli, G.; Stoykov, A.; Tassielli, G. F.; Toyoda, K.; Uchiyama, Y.; Usami, M.; Voena, C.; Yanai, K.; Yudin, Yu. V.
The European physical journal. C, Particles and fields, 09/2020, Volume: 80, Issue: 9Journal Article
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, μ + → e + X , X → γ γ . This search uses a dataset resulting from 7.5 × 10 14 stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c 2 for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c 2 , down to O ( 10 - 11 ) at 90% confidence level.
