A search for \(\mu^+\to e^+\gamma\) with the first dataset of the MEG II experiment

• Published in: arXiv.org 2023-10
• Main Authors: collaboration, MEG II, Afanaciev, K, Baldini, A M, Ban, S, Baranov, V, Benmansour, H, Biasotti, M, Boca, G, Cattaneo, P W, Cavoto, G, Cei, F, Chiappini, M, Chiarello, G, Corvaglia, A, Cuna, F, G Dal Maso, De Bari, A, De Gerone, M, L Ferrari Barusso, Francesconi, M, Galli, L, Gallucci, G, Gatti, F, Gerritzen, L, Grancagnolo, F, Grandoni, E G, Grassi, M, Grigoriev, D N, Hildebrandt, M, Ieki, K, Ignatov, F, Ikeda, F, Iwamoto, T, Karpov, S, P -R Kettle, Khomutov, N, Kobayashi, S, Kolesnikov, A, Kravchuk, N, Krylov, V, Kuchinskiy, N, Kyle, W, Libeiro, T, Malyshev, V, Matsushita, A, Meucci, M, Mihara, S, Molzon, W, Mori, Toshinori, Nakao, M, Nicolò, D, Nishiguchi, H, Ochi, A, Ogawa, S, Onda, R, Ootani, W, Oya, A, Palo, D, Panareo, M, Papa, A, Pettinacci, V, Popov, A, Renga, F, Ritt, S, Rossella, M, Rozhdestvensky, A, Schwendimann, P, Shimada, K, Signorelli, G, Takahashi, M, Tassielli, G F, Toyoda, K, Uchiyama, Y, Usami, M, Venturini, A, Vitali, B, Voena, C, Yamamoto, K, Yanai, K, Yonemoto, T, Yoshida, K, Yudin, Yu V
• Format: Article
• Language: English
• ISSN: 2331-8422

The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay \(\mu^+\to e^+\gamma\) from data taken in the first physics run in 2021. No excess of events over the expected background is observed, yielding an upper limit on the branching ratio of B(\(\mu^+\to e^+\gamma\)) < \(7.5 \times 10^{-13}\) (90% C.L.). The combination of this result and the limit obtained by MEG gives B(\(\mu^+\to e^+\gamma\)) < \(3.1 \times 10^{-13}\) (90% C.L.), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022-2023, and data-taking will continue in the coming years.