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arXiv · 2005.00339

Search for lepton flavour violating muon decay mediated by a new light particle in the MEG experiment

A. M. Baldini·F. Berg·M. Biasotti·G. Boca·P. W. Cattaneo·G. Cavoto·F. Cei·M. Chiappini·G. Chiarello·C. Chiri·A. Corvaglia·A. de Bari·M. De Gerone·M. Francesconi·L. Galli·F. Gatti·F. Grancagnolo·M. Grassi·D. N. Grigoriev·M. Hildebrandt·Z. Hodge·K. Ieki·F. Ignatov·R. Iwai·T. Iwamoto·S. Kobayashi·P. -R. Kettle·W. Kyle·N. Khomutov·A. Kolesnikov·N. Kravchuk·N. Kuchinskiy·T. Libeiro·G. M. A. Lim·V. Malyshev·N. Matsuzawa·M. Meucci·S. Mihara·W. Molzon·Toshinori Mori·A. Mtchedilishvili·M. Nakao·H. Natori·D. Nicolò·H. Nishiguchi·M. Nishimura·S. Ogawa·R. Onda·W. Ootani·A. Oya·D. Palo·M. Panareo·A. Papa·V. Pettinacci·G. Pizzigoni·A. Popov·F. Renga·S. Ritt·A. Rozhdestvensky·M. Rossella·R. Sawada·P. Schwendimann·G. Signorelli·A. Stoykov·G. F. Tassielli·K. Toyoda·Y. Uchiyama·M. Usami·C. Voena·K. Yanai·Yu. V. Yudin
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Abstract

We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, $\mu^+ \to \mathrm{e}^+\mathrm{X}, \mathrm{X} \to \gamma\gamma$. This search uses a dataset resulting from $7.5\times 10^{14}$ 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 $\mathcal{O}(10^{-11})$ at 90\% confidence level.

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A. M. Baldini, F. Berg, M. Biasotti, G. Boca, P. W. Cattaneo, G. Cavoto, F. Cei, M. Chiappini, G. Chiarello, C. Chiri, A. Corvaglia, A. de Bari, M. De Gerone, M. Francesconi, L. Galli, F. Gatti, F. Grancagnolo, M. Grassi, D. N. Grigoriev, M. Hildebrandt, Z. Hodge, K. Ieki, F. Ignatov, R. Iwai, T. Iwamoto, S. Kobayashi, P. -R. Kettle, W. Kyle, N. Khomutov, A. Kolesnikov, N. Kravchuk, N. Kuchinskiy, T. Libeiro, G. M. A. Lim, V. Malyshev, N. Matsuzawa, M. Meucci, S. Mihara, W. Molzon, Toshinori Mori, A. Mtchedilishvili, M. Nakao, H. Natori, D. Nicolò, H. Nishiguchi, M. Nishimura, S. Ogawa, R. Onda, W. Ootani, A. Oya, D. Palo, M. Panareo, A. Papa, V. Pettinacci, G. Pizzigoni, A. Popov, F. Renga, S. Ritt, A. Rozhdestvensky, M. Rossella, R. Sawada, P. Schwendimann, G. Signorelli, A. Stoykov, G. F. Tassielli, K. Toyoda, Y. Uchiyama, M. Usami, C. Voena, K. Yanai, Yu. V. Yudin. 2020-05-01. Search for lepton flavour violating muon decay mediated by a new light particle in the MEG experiment. https://doi.org/10.1140/epjc/s10052-020-8364-1

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