First measurement of the low-momentum negative-muon beam for the muon-to-electron conversion experiment at J-PARC
Year: 2026
Type: preprint
Abstract: The COMET Phase-$α$ experiment, the initial beam-operation stage of the COMET muon-to-electron conversion programme at J-PARC, took place in 2023 and marked the first beam operation at the COMET facility. It served to commission the delivery of a bunched, slow-extracted 8 GeV proton beam and the muon beamline. Its objective was to demonstrate experimentally that low-momentum negative muons could be transported to the experimental area through the Transport Solenoid (TS). We report a measurement of the transported muon beam using the Range Counter, a dedicated detector that identifies stopped negative muons by detecting delayed electrons emitted after the muons stop in a copper absorber. From the measured decay-time spectra, we reconstruct the number of stopped muons, the corresponding momentum spectrum, and the transverse beam profile. The observation of the stopped-muon component demonstrates that slow negative muons were transported through the TS to the experimental area. The reconstructed momentum spectrum indicates that the transported beam is concentrated in the low-momentum region. The non-uniform transverse profile is qualitatively consistent with charge drift in the curved solenoidal magnetic field. A Geant4-based simulation reproduces the overall dependence on degrader thickness and detector position; the measured yields are systematically higher by roughly 30%. These results provide the first experimental benchmark of low-momentum negative-muon transport in COMET and establish the basis for future beam characterisation and production studies.
Source: arXiv (Cornell University)
Authors: The COMET Collaboration, Oishi, K., Abramishvili, R., Adamov, G., Angelique, J. C., Aoki, K., Aoki, M., Arimoto, Y., Az, A. N. B., Bagaturia, I., Bauer, D., Bouillaud, T., Del Buono, L., Cârloganu, C., Chadeau, N., Chen, Y., Chetry, P., Chokheli, D., Clouvel, T., Dauncey, P. D., Dekkers, S., Derveni, R., Devidze, G., Dornan, P. J., Dubouchet, M. T., Epshteyn, L. B., Evtoukhovitch, I., Evtoukhovitch, P., Faure, G., Fayer, S., Fedotovich, G. V., Fujii, Y., Fukao, Y., George, E., Gillies, E. L., Gouzevitch, M., Grigoriev, D. N., Hamada, E., Hashim, I. H., Hashimoto, S., Higashide, M., Higuchi, Y., Hiroshima, N., Igarashi, Y., Ignatov, F. V., Iio, M., Ikeno, M., Ishibashi, K., Itahashi, T., Jansen, A., Jeena, R., Jeremy, O., Jiang, X., Jonsson, P. M., Kageyama, Y., Kalinnikov, V., Kaneva, E., Kapusta, F., Kawagoe, K., Kawashima, R., Kazak, N., Khvedelidze, A., Kojima, Y., Kozyrev, A. N., Krikler, B., Kuno, Y., Kuribayashi, S., Kurochkin, Y., Kurosawa, N., Kurup, A., Ladhams, K., Lebrun, P., Lee, M. J., Li, H., Li, W., Litchfield, R. P., Lomidze, D., Lomidze, I., Macharashvili, G., Makida, Y., Makimura, S., Matsumoto, G., Matsumoto, S., Melnik, A., Miao, H., Mihara, S., Miles, A., Miyataki, M., Miyazaki, Y., Mizuno, T., Moritsu, M., Muto, R., Nagai, R., Nagashima, H., Nakai, Y., Nakamoto, T., Nakamura, Y., Nakatsugawa, Y., Nakazawa, Y., Nash, J., Nasrullah, M. A. S., Nguyen, T. M., Niess, V., Ning, Y. S., Nishiguchi, H., Nishihara, M., Noguchi, K., Nor, N. H. M., Norjoharuddeen, N., Ogitsu, T., Ohata, H., Ohuchi, N., Okabe, K., Okamura, T., Okurano, H., Oonaka, M., Pasternak, J., Paulau, A., Pieters, D., Raspal, V., Razali, R., Razquin, A., Roth, W., Sabirov, B., Saito, T., Sakamoto, H., Sarin, P., Sasaki, K. I., Sasaki, R., Sato, A., Sato, J., Sendai, H., Shigyo, N., Shinjo, M., Shioya, Z., Shoji, M., Shoukavy, Dz., Da Silva, W., Simonenko, A., Stöckinger, D., Sumi, N., Sumimura, A., Sun, S., Suzuki, J., Takami, S., Tanaka, S., Tang, J., Tojo, J., Tomizawa, M., Toriashvili, T., Tran, N., Tsamalaidze, Z., Tsverava, N., Uchida, T., Uchida, Y., Uchiyama, Y., Ueda, S., Ueno, K., Uesaka, Y., Vasileuskaya, D., Velicheva, E., Wong, M. L., Wong, T. S., Wu, C., Xing, T., Xu, Y., Yamada, C., Yamaguchi, H., Yamanaka, M., Yang, Y., Yao, W., Yeo, B., Yoshida, H., Yoshida, M., Yoshii, M., Yoshikawa, D., Yoshioka, T., Yuan, Y., Yudin, Yu. V., Yussup, N., Yusuff, I., Zhang, J., Zhang, Y., Zhang, Z., Zhou, Y., Zuber, K.
Institutions: High Energy Accelerator Research Organization, Imperial College London, Georgian Technical University, Centre National de la Recherche Scientifique, École Nationale Supérieure d'Ingénieurs de Caen, Laboratoire de Physique Corpusculaire de Caen, Institut National de Physique Nucléaire et de Physique des Particules, Université de Caen Normandie, The University of Osaka, University of Technology Malaysia, Kyushu University, Université Clermont Auvergne, Laboratoire de Physique de Clermont Auvergne, Toshiko Yuasa Laboratory, Sun Yat-sen University, Indian Institute of Technology Bombay, Joint Institute for Nuclear Research, Monash University, Tbilisi State University, Institut de Physique des 2 Infinis de Lyon, Budker Institute of Nuclear Physics, Institut de Physique, Yokohama National University, Technische Universität Dresden, Institute of High Energy Physics, University of Chinese Academy of Sciences, Université Paris Cité, Sorbonne Université, Laboratoire de Physique Nucléaire et de Hautes Énergies, National Academy of Sciences of Belarus, B.I. Stepanov Institute of Physics, Sungkyunkwan University, University of Glasgow, National Institute of Technology, Akashi College, Wakayama Medical University, Shiga University, FPT University, University of Malaya, Hiroshima Institute of Technology, Korea Advanced Institute of Science and Technology, Malaysian Nuclear Agency, National University of Malaysia
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Natural Science Foundation of Guangzhou City, European Commission, National Research Foundation, Deutsche Forschungsgemeinschaft, National Natural Science Foundation of China, Chinese Academy of Sciences, Joint Institute for Nuclear Research, Shota Rustaveli National Science Foundation, Universiti Teknologi Malaysia, Ministry of Science and Higher Education of the Russian Federation, Science and Technology Facilities Council, Institut National de Physique Nucléaire et de Physique des Particules, Basic and Applied Basic Research Foundation of Guangdong Province
Awards: G1001717021, G1868831564, Probes of new physics and technological advancements from particle and gravitational wave physics experiments. A cooperative Europe - United States - Asia effort., G2928488918, G4305232107, G5656979059, G6856879406, G7101266724, Designing, Optimising and Validating the Beam Measurement Programme at the New Intense Muon Beam Line for the COMET Muon-to-Electron Search Experiment, G8873840955
OpenAlex ID: W7220360227