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Search for Feebly Interacting Particles in B Decays with Missing Energy at Belle

M. Abumusabh, I. Adachi, L. Aggarwal, H. Ahmed, Y. Ahn, H. Aihara, N. Akopov, S. Alghamdi, M. Alhakami et al. (The Belle and Belle II Collaborations)

M. Alhakami, A. Aloisio, N. Althubiti, K. Amos, N. Anh Ky, C. Antonioli, D. M. Asner, H. Atmacan, T. Aushev, R. Ayad, V. Babu, H. Bae, N. K. Baghel, S. Bahinipati, P. Bambade, Sw. Banerjee, M. Barrett, M. Bartl, J. Baudot, A. Beaubien, F. Becherer, J. Becker, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, F. Bianchi, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, A. Bondar, G. Bonvicini, J. Borah, A. Boschetti, A. Bozek, M. Bračko, P. Branchini, N. Brenny, T. E. Browder, A. Budano, S. Bussino, Q. Campagna, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, P. Chang, P. Cheema, C. Chen, L. Chen, B. G. Cheon, C. Cheshta, H. Chetri, K. Chilikin, J. Chin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, S. Chutia, J. Cochran, J. A. Colorado-Caicedo, I. Consigny, L. Corona, J. X. Cui, E. De La Cruz-Burelo, S. A. De La Motte, G. de Marino, G. De Nardo, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, R. Dhayal, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, X. Dong, G. Dujany, P. Ecker, D. Epifanov, R. Farkas, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, F. Forti, B. G. Fulsom, A. Gabrielli, A. Gale, E. Ganiev, M. Garcia-Hernandez, R. Garg, L. Gärtner, G. Gaudino, V. Gaur, V. Gautam, A. Gellrich, G. Ghevondyan, D. Ghosh, H. Ghumaryan, G. Giakoustidis, R. Giordano, A. Giri, P. Gironella Gironell, A. Glazov, B. Gobbo, R. Godang, O. Gogota, P. Goldenzweig, E. Graziani, D. Greenwald, K. Gudkova, I. Haide, Y. Han, H. Hayashii, S. Hazra, C. Hearty, M. T. Hedges, A. Heidelbach, G. Heine, I. Heredia de la Cruz, M. Hernández Villanueva, T. Higuchi, M. Hoek, M. Hohmann, R. Hoppe, P. Horak, X. T. Hou, C.-L. Hsu, T. Humair, T. Iijima, G. Inguglia, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, P. Jackson, W. W. Jacobs, E.-J. Jang, Q. P. Ji, S. Jia, Y. Jin, A. Johnson, A. B. Kaliyar, J. Kandra, K. H. Kang, S. Kang, G. Karyan, F. Keil, C. Ketter, C. Kiesling, D. Y. Kim, J.-Y. Kim, K.-H. Kim, H. Kindo, K. Kinoshita, P. Kodyš, T. Koga, S. Kohani, K. Kojima, A. Korobov, S. Korpar, E. Kovalenko, R. Kowalewski, P. Križan, P. Krokovny, T. Kuhr, D. Kumar, K. Kumara, T. Kunigo, A. Kuzmin, Y.-J. Kwon, S. Lacaprara, T. Lam, J. S. Lange, T. S. Lau, M. Laurenza, R. Leboucher, F. R. Le Diberder, H. Lee, M. J. Lee, C. Lemettais, P. Leo, P. M. Lewis, C. Li, H.-J. Li, L. K. Li, Q. M. Li, W. Z. Li, Y. Li, Y. B. Li, Y. P. Liao, J. Libby, J. Lin, S. Lin, Z. Liptak, M. H. Liu, Q. Y. Liu, Z. Liu, D. Liventsev, S. Longo, A. Lozar, C. Lyu, J. L. Ma, Y. Ma, M. Maggiora, S. P. Maharana, R. Maiti, G. Mancinelli, R. Manfredi, E. Manoni, M. Mantovano, D. Marcantonio, M. Marfoli, C. Marinas, C. Martellini, A. Martens, T. Martinov, L. Massaccesi, M. Masuda, D. Matvienko, S. K. Maurya, M. Maushart, J. A. McKenna, Z. Mediankin Gruberová, R. Mehta, F. Meier, D. Meleshko, M. Merola, C. Miller, M. Mirra, K. Miyabayashi, H. Miyake, R. Mizuk, G. B. Mohanty, S. Moneta, A. L. Moreira de Carvalho, H.-G. Moser, M. Mrvar, H. Murakami, I. Nakamura, M. Nakao, Y. Nakazawa, M. Naruki, Z. Natkaniec, A. Natochii, M. Nayak, M. Neu, S. Nishida, R. Nomaru, S. Ogawa, H. Ono, F. Otani, G. Pakhlova, A. Panta, S. Pardi, K. Parham, J. Park, K. Park, S.-H. Park, A. Passeri, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, M. Piccolo, L. E. Piilonen, P. L. M. Podesta-Lerma, T. Podobnik, C. Praz, S. Prell, E. Prencipe, M. T. Prim, S. Privalov, H. Purwar, P. Rados, S. Raiz, K. Ravindran, J. U. Rehman, M. Reif, S. Reiter, L. Reuter, D. Ricalde Herrmann, I. Ripp-Baudot, G. Rizzo, S. H. Robertson, J. M. Roney, A. Rostomyan, N. Rout, S. Saha, L. Salutari, D. A. Sanders, S. Sandilya, L. Santelj, C. Santos, V. Savinov, B. Scavino, S. Schneider, G. Schnell, M. Schnepf, K. Schoenning, C. Schwanda, A. J. Schwartz, Y. Seino, K. Senyo, J. Serrano, M. E. Sevior, C. Sfienti, W. Shan, G. Sharma, X. D. Shi, T. Shillington, T. Shimasaki, J.-G. Shiu, D. Shtol, A. Sibidanov, F. Simon, J. Skorupa, M. Sobotzik, A. Soffer, A. Sokolov, E. Solovieva, S. Spataro, K. Špenko, B. Spruck, M. Starič, P. Stavroulakis, S. Stefkova, L. Stoetzer, R. Stroili, M. Sumihama, K. Sumisawa, M. Takahashi, M. Takizawa, U. Tamponi, S. Tanaka, S. S. Tang, K. Tanida, F. Tenchini, F. Testa, A. Thaller, T. Tien Manh, O. Tittel, R. Tiwary, E. Torassa, K. Trabelsi, F. F. Trantou, I. Tsaklidis, I. Ueda, K. Unger, Y. Unno, K. Uno, S. Uno, P. Urquijo, Y. Ushiroda, S. E. Vahsen, R. van Tonder, K. E. Varvell, M. Veronesi, V. S. Vismaya, L. Vitale, V. Vobbilisetti, R. Volpe, M. Wakai, S. Wallner, M.-Z. Wang, A. Warburton, M. Watanabe, S. Watanuki, C. Wessel, E. Won, X. P. Xu, B. D. Yabsley, W. Yan, W. Yan, J. Yelton, K. Yi, J. H. Yin, K. Yoshihara, J. Yuan, L. Zani, F. Zeng, M. Zeyrek, B. Zhang, V. Zhilich, J. S. Zhou, Q. D. Zhou, L. Zhu, and R. Žlebčík (The Belle and Belle II Collaborations)

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Phys. Rev. Lett. 136, 231802 – Published 12 June, 2026

DOI: https://doi.org/10.1103/1rl4-j3np

Abstract

We present a search for an invisible hidden-sector particle Xinv, produced in B0→D¯0Xinv and B±→hXinv decays, where h=π±, K±, Ds±, p±. The search is performed using e+e− collision data recorded with the Belle detector, corresponding to 711  fb−1. No significant signal is observed. We set 90% confidence level upper limits ranging between 10−4 and 10−6 on the branching fraction B(B→hXinv) as a function of mXinv. Corresponding limits are set on B(B→hX)×B(X→γγ) for lifetimes cτX between 10  μm and 10 m. Many of these limits are the first direct constraints on their respective decays. Our results provide the most stringent exclusion limits to date on the branching fractions for all search channels, and exclude previously unexplored regions of parameter space relevant to several new physics models.

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Phys. Rev. Lett. 136, 231802– Published 12 June, 2026
  • Received 11 January 2026
  • Accepted 23 April 2026
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