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arXiv · 2504.15711

New limit on the \mu+->e+\gamma decay with the MEG II experiment

K. Afanaciev·A. M. Baldini·S. Ban·H. Benmansour·G. Boca·P. W. Cattaneo·G. Cavoto·F. Cei·M. Chiappini·A. Corvaglia·G. Dal Maso·A. De Bari·M. De Gerone·L. Ferrari Barusso·M. Francesconi·L. Galli·G. Gallucci·F. Gatti·L. Gerritzen·F. Grancagnolo·E. G. Grandoni·M. Grassi·D. N. Grigoriev·M. Hildebrandt·F. Ignatov·F. Ikeda·T. Iwamoto·S. Karpov·P. -R. Kettle·N. Khomutov·A. Kolesnikov·N. Kravchuk·V. Krylov·N. Kuchinskiy·F. Leonetti·W. Li·V. Malyshev·A. Matsushita·S. Mihara·W. Moltzon·Toshinori Mori·D. Nicolo'·H. Nishiguchi·A. Ochi·H. Ogawa·W. Ootani·A. Oya·D. Palo·M. Panareo·A. Papa·D. Pasciuto·A. Popov·F. Renga·S. Ritt·M. Rossella·A. Rozhdestvensky·S. Scarpellini·G. Signorelli·H. Suzuki·M. Takahashi·Y. Uchiyama·R. Umakoshi·A. Venturini·B. Vitali·C. Voena·K. Yamamoto·R. Yokota·T. Yonemoto
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Abstract

This letter reports the result of the search for the decay \mu+->e+\gamma undertaken at the Paul Scherrer Institut in Switzerland with the MEG II experiment using the data collected in the 2021- 2022 physics runs. The sensitivity of this search is 2.2x10-13, a factor of 2.4 better than that of the full MEG dataset and obtained in a data taking period of about one fourth that of MEG, thanks to the superior performances of the new detector. The result is consistent with the expected background, yielding an upper limit on the branching ratio of B(\mu+->e+\gamma)<1.5 x 10-13 (90 % C.L.). Additional improvements are expected with the data collected during the years 2023-2024. The data-taking will continue in the coming years.

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K. Afanaciev, A. M. Baldini, S. Ban, H. Benmansour, G. Boca, P. W. Cattaneo, G. Cavoto, F. Cei, M. Chiappini, A. Corvaglia, G. Dal Maso, A. De Bari, M. De Gerone, L. Ferrari Barusso, M. Francesconi, L. Galli, G. Gallucci, F. Gatti, L. Gerritzen, F. Grancagnolo, E. G. Grandoni, M. Grassi, D. N. Grigoriev, M. Hildebrandt, F. Ignatov, F. Ikeda, T. Iwamoto, S. Karpov, P. -R. Kettle, N. Khomutov, A. Kolesnikov, N. Kravchuk, V. Krylov, N. Kuchinskiy, F. Leonetti, W. Li, V. Malyshev, A. Matsushita, S. Mihara, W. Moltzon, Toshinori Mori, D. Nicolo', H. Nishiguchi, A. Ochi, H. Ogawa, W. Ootani, A. Oya, D. Palo, M. Panareo, A. Papa, D. Pasciuto, A. Popov, F. Renga, S. Ritt, M. Rossella, A. Rozhdestvensky, S. Scarpellini, G. Signorelli, H. Suzuki, M. Takahashi, Y. Uchiyama, R. Umakoshi, A. Venturini, B. Vitali, C. Voena, K. Yamamoto, R. Yokota, T. Yonemoto. 2025-04-22. New limit on the \mu+->e+\gamma decay with the MEG II experiment. https://arxiv.org/abs/2504.15711

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