A search for with the first dataset of the MEG II experiment

K. Afanaciev; A. M. Baldini; S. Ban; V. Baranov; H. Benmansour; M. Biasotti; G. Boca; P. W. Cattaneo; G. Cavoto; F. Cei; M. Chiappini; G. Chiarello; A. Corvaglia; F. Cuna; 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; K. Ieki; F. Ignatov; F. Ikeda; T. Iwamoto; S. Karpov; P.-R. Kettle; N. Khomutov; S. Kobayashi; A. Kolesnikov; N. Kravchuk; V. Krylov; N. Kuchinskiy; W. Kyle; T. Libeiro; V. Malyshev; A. Matsushita; M. Meucci; S. Mihara; W. Molzon; Toshinori Mori; M. Nakao; D. Nicolò; H. Nishiguchi; A. Ochi; S. Ogawa; R. Onda; W. Ootani; A. Oya; D. Palo; M. Panareo; A. Papa; V. Pettinacci; A. Popov; F. Renga; S. Ritt; M. Rossella; A. Rozhdestvensky; P. Schwendimann; K. Shimada; G. Signorelli; M. Takahashi; G. F. Tassielli; K. Toyoda; Y. Uchiyama; M. Usami; A. Venturini; B. Vitali; C. Voena; K. Yamamoto; K. Yanai; T. Yonemoto; K. Yoshida; Yu. V. Yudin

doi:10.1140/epjc/s10052-024-12416-2

2024 Impact factor 4.8

Particles and Fields

Open Access

This article has an erratum: [https://doi.org/10.1140/epjc/s10052-024-13352-x]

Eur. Phys. J. C (2024) 84: 216
https://doi.org/10.1140/epjc/s10052-024-12416-2

Regular Article - Experimental Physics

A search for $μ^{+} \to e^{+} γ$ $\upmu ^+ \rightarrow \textrm{e}^+ \upgamma$ with the first dataset of the MEG II experiment

K. Afanaciev¹, A. M. Baldini², S. Ban⁴, V. Baranov¹, H. Benmansour²^,3, M. Biasotti⁵, G. Boca⁷^,8, P. W. Cattaneo¹^,7^h, G. Cavoto⁹^,10, F. Cei²^,3, M. Chiappini²^,3, G. Chiarello¹¹^,23, A. Corvaglia¹¹, F. Cuna¹¹^,12^,24, G. Dal Maso¹³^,14, A. De Bari⁷, M. De Gerone⁵, L. Ferrari Barusso⁵^,6, M. Francesconi¹⁵, L. Galli², G. Gallucci⁵, F. Gatti⁵^,6, L. Gerritzen⁴, F. Grancagnolo¹¹, E. G. Grandoni²^,3, M. Grassi², D. N. Grigoriev¹⁶^,17^,18, M. Hildebrandt¹³, K. Ieki⁴, F. Ignatov¹⁹, F. Ikeda⁴, T. Iwamoto⁴, S. Karpov¹⁶^,18, P.-R. Kettle¹³, N. Khomutov¹, S. Kobayashi⁴, A. Kolesnikov¹, N. Kravchuk¹, V. Krylov¹, N. Kuchinskiy¹, W. Kyle²⁰, T. Libeiro²⁰, V. Malyshev¹, A. Matsushita⁴, M. Meucci⁹^,10, S. Mihara²¹, W. Molzon²⁰, Toshinori Mori⁴, M. Nakao⁴, D. Nicolò²^,3, H. Nishiguchi²¹, A. Ochi²², S. Ogawa⁴, R. Onda⁴, W. Ootani⁴, A. Oya⁴, D. Palo²⁰, M. Panareo¹¹^,12, A. Papa²^,3^,13, V. Pettinacci⁹, A. Popov¹⁶^,18, F. Renga⁹, S. Ritt¹³, M. Rossella⁷, A. Rozhdestvensky¹, P. Schwendimann¹³, K. Shimada⁴, G. Signorelli², M. Takahashi²², G. F. Tassielli¹¹^,12^,25, K. Toyoda⁴, Y. Uchiyama⁴^,22, M. Usami⁴, A. Venturini²^,3, B. Vitali²^,10, C. Voena⁹^,10, K. Yamamoto⁴, K. Yanai⁴, T. Yonemoto⁴, K. Yoshida⁴, Yu. V. Yudin¹⁶^,18 and MEG II Collaboration

¹ Joint Institute for Nuclear Research, 141980, Dubna, Russia
² INFN Sezione di Pisa, Pisa, Italy
³ Dipartimento di Fisica dell’Università, Largo B. Pontecorvo 3, 56127, Pisa, Italy
⁴ ICEPP, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033, Tokyo, Japan
⁵ INFN Sezione di Genova, Genoa, Italy
⁶ Dipartimento di Fisica dell’Università, Via Dodecaneso 33, 16146, Genoa, Italy
⁷ INFN Sezione di Pavia, Pavia, Italy
⁸ Dipartimento di Fisica dell’Università, Via Bassi 6, 27100, Pavia, Italy
⁹ INFN Sezione di Roma, Rome, Italy
¹⁰ Dipartimento di Fisica dell’Università “Sapienza”, Piazzale A. Moro, 00185, Rome, Italy
¹¹ INFN Sezione di Lecce, Lecce, Italy
¹² Dipartimento di Matematica e Fisica dell’Università del Salento, Via per Arnesano, 73100, Lecce, Italy
¹³ Paul Scherrer Institut PSI, 5232, Villigen, Switzerland
¹⁴ Institute for Particle Physics and Astrophysics, ETH Zürich, Otto-Stern-Weg 5, 8093, Zurich, Switzerland
¹⁵ INFN Sezione di Napoli, Via Cintia, 80126, Naples, Italy
¹⁶ Budker Institute of Nuclear Physics of Siberian Branch of Russian Academy of Sciences, 630090, Novosibirsk, Russia
¹⁷ Novosibirsk State Technical University, 630092, Novosibirsk, Russia
¹⁸ Novosibirsk State University, 630090, Novosibirsk, Russia
¹⁹ Oliver Lodge Laboratory, University of Liverpool, L69 7ZE, Liverpool, UK
²⁰ University of California, 92697, Irvine, CA, USA
²¹ KEK, High Energy Accelerator Research Organization, 1-1 Oho, 305-0801, Tsukuba, Ibaraki, Japan
²² Kobe University, 1-1 Rokkodai-cho, Nada-ku, 657-8501, Kobe, Hyogo, Japan
²³ Department of Engineering, University of Palermo, Viale delle Scienze, Building 9, 90128, Palermo, Italy
²⁴ INFN Sezione di Bari, Via Giovanni Amendola, 173, 70126, Bari, Italy
²⁵ Dipartimento di Medicina e Chirurgia, Università LUM “Giuseppe Degennaro”, 70010, Casamassima, Bari, Italy

^h paolo.cattaneo@pv.infn.it

Received: 19 October 2023
Accepted: 5 January 2024
Published online: 1 March 2024

Abstract

The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay $μ^{+} \to e^{+} γ$ $\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma$ 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 $B (μ^{+} \to e^{+} γ) < 7.5 \times 10^{- 13}$ ${\mathcal {B}} (\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma ) < 7.5 \times 10^{-13}$ (90% CL). The combination of this result and the limit obtained by MEG gives $B (μ^{+} \to e^{+} γ) < 3.1 \times 10^{- 13}$ ${\mathcal {B}} (\upmu ^+ \rightarrow {\textrm{e}}^+ \upgamma ) < 3.1 \times 10^{-13}$ (90% CL), 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.

V. Baranov: Deceased.

An erratum to this article is available online at https://doi.org/10.1140/epjc/s10052-024-13352-x.

Erratum to this article: https://doi.org/10.1140/epjc/s10052-024-13352-x

© The Author(s) 2024

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