I Adachi, P Ahlburg, H Aihara, N Akopov, A Aloisio, N Anh Ky, D M Asner, H Atmacan, T Aushev, V Aushev, T Aziz, V Babu, S Baehr, P Bambade, Sw Banerjee, V Bansal, M Barrett, J Baudot, J Becker, P K Behera, J V Bennett, E Bernieri, F U Bernlochner, M Bertemes, M Bessner, S Bettarini, F Bianchi, D Biswas, A Bozek, M Bračko, P Branchini, R A Briere, T E Browder, A Budano, L Burmistrov, S Bussino, M Campajola, L Cao, G Casarosa, C Cecchi, D Červenkov, M-C Chang, R Cheaib, V Chekelian, Y Q Chen, Y-T Chen, B G Cheon, K Chilikin, K Cho, S Cho, S-K Choi, S Choudhury, D Cinabro, L Corona, L M Cremaldi, S Cunliffe, T Czank, F Dattola, E De La Cruz-Burelo, G De Nardo, M De Nuccio, G De Pietro, R de Sangro, M Destefanis, S Dey, A De Yta-Hernandez, F Di Capua, Z Doležal, I Domínguez Jiménez, T V Dong, K Dort, D Dossett, S Dubey, S Duell, G Dujany, S Eidelman, M Eliachevitch, J E Fast, T Ferber, D Ferlewicz, G Finocchiaro, S Fiore, A Fodor, F Forti, B G Fulsom, E Ganiev, M Garcia-Hernandez, R Garg, V Gaur, A Gaz, A Gellrich, J Gemmler, T Geßler, R Giordano, A Giri, B Gobbo, R Godang, P Goldenzweig, B Golob, P Gomis, W Gradl, E Graziani, D Greenwald, Y Guan, C Hadjivasiliou, S Halder, T Hara, O Hartbrich, K Hayasaka, H Hayashii, C Hearty, M T Hedges, I Heredia de la Cruz, M Hernández Villanueva, A Hershenhorn, T Higuchi, E C Hill, M Hoek, C-L Hsu, Y Hu, T Iijima, K Inami, G Inguglia, J Irakkathil Jabbar, A Ishikawa, R Itoh, Y Iwasaki, W W Jacobs, D E Jaffe, E-J Jang, H B Jeon, S Jia, Y Jin, C Joo, K K Joo, J Kahn, H Kakuno, A B Kaliyar, J Kandra, G Karyan, Y Kato, T Kawasaki, B H Kim, C-H Kim, D Y Kim, K-H Kim, S-H Kim, Y K Kim, Y Kim, T D Kimmel, H Kindo, C Kleinwort, P Kodyš, T Koga, S Kohani, I Komarov, S Korpar, N Kovalchuk, T M G Kraetzschmar, P Križan, R Kroeger, P Krokovny, T Kuhr, J Kumar, M Kumar, R Kumar, K Kumara, S Kurz, A Kuzmin, Y-J Kwon, S Lacaprara, C La Licata, L Lanceri, J S Lange, K Lautenbach, I-S Lee, S C Lee, P Leitl, D Levit, L K Li, Y B Li, J Libby, K Lieret, L Li Gioi, Z Liptak, Q Y Liu, D Liventsev, S Longo, T Luo, Y Maeda, M Maggiora, E Manoni, S Marcello, C Marinas, A Martini, M Masuda, T Matsuda, K Matsuoka, D Matvienko, F Meggendorfer, J C Mei, F Meier, M Merola, F Metzner, M Milesi, C Miller, K Miyabayashi, H Miyake, R Mizuk, K Azmi, G B Mohanty, T Moon, T Morii, H-G Moser, F Mueller, F J Müller, Th Muller, G Muroyama, R Mussa, E Nakano, M Nakao, M Nayak, G Nazaryan, D Neverov, C Niebuhr, N K Nisar, S Nishida, K Nishimura, M Nishimura, B Oberhof, K Ogawa, Y Onishchuk, H Ono, Y Onuki, P Oskin, H Ozaki, P Pakhlov, G Pakhlova, A Paladino, A Panta, E Paoloni, H Park, B Paschen, A Passeri, A Pathak, S Paul, T K Pedlar, I Peruzzi, R Peschke, R Pestotnik, M Piccolo, L E Piilonen, V Popov, C Praz, E Prencipe, M T Prim, M V Purohit, P Rados, R Rasheed, S Reiter, M Remnev, P K Resmi, I Ripp-Baudot, M Ritter, G Rizzo, L B Rizzuto, S H Robertson, D Rodríguez Pérez, J M Roney, C Rosenfeld, A Rostomyan, N Rout, G Russo, D Sahoo, Y Sakai, S Sandilya, A Sangal, L Santelj, P Sartori, Y Sato, V Savinov, B Scavino, J Schueler, C Schwanda, R M Seddon, Y Seino, A Selce, K Senyo, C Sfienti, C P Shen, J-G Shiu, B Shwartz, A Sibidanov, F Simon, R J Sobie, A Soffer, A Sokolov, E Solovieva, S Spataro, B Spruck, M Starič, S Stefkova, Z S Stottler, R Stroili, J Strube, M Sumihama, T Sumiyoshi, D J Summers, S Y Suzuki, M Tabata, M Takizawa, U Tamponi, S Tanaka, K Tanida, N Taniguchi, P Taras, F Tenchini, E Torassa, K Trabelsi, T Tsuboyama, M Uchida, K Unger, Y Unno, S Uno, Y Ushiroda, S E Vahsen, R van Tonder, G S Varner, K E Varvell, A Vinokurova, L Vitale, A Vossen, M Wakai, H M Wakeling, W Wan Abdullah, C H Wang, M-Z Wang, A Warburton, M Watanabe, J Webb, S Wehle, C Wessel, J Wiechczynski, H Windel, E Won, B Yabsley, S Yamada, W Yan, S B Yang, H Ye, J H Yin, M Yonenaga, C Z Yuan, Y Yusa, L Zani, Z Zhang, V Zhilich, Q D Zhou, X Y Zhou, V I Zhukova
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z^{'}. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z^{'} in the process e^{+}e^{-}→μ^{+}μ^{-}Z^{'} and of a lepton-flavor-violating Z^{'} in e^{+}e^{-}→e^{±}μ^{∓}Z^{'}. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an L_{μ}-L_{τ} theory, into upper limits on the Z^{'} coupling constant at the level of 5×10^{-2}-1 for M_{Z^{'}}≤6 GeV/c^{2}...
April 10, 2020: Physical Review Letters