Adachi, I.Adamczyk, K.Aggarwal, L.Ahmed, H.Aihara, H.Akopov, N.Aloisio, A.Anh Ky, N.Asner, D. M.Atmacan, H.Aushev, T.Aushev, V.Aversano, M.Babu, V.Bae, H.Bahinipati, S.Bambade, P.Banerjee, S.Bansal, S.Barrett, M.Baudot, J.Bauer, M.Baur, A.Beaubien, A.Becker, J.Behera, P. K.Bennett, J. V.Bernieri, E.Bernlochner, F. U.Bertacchi, V.Bertemes, M.Bertholet, E.Bessner, M.Bettarini, S.Bhardwaj, V.Bhuyan, B.Bianchi, F.Bilka, T.Bilokin, S.Biswas, D.Bobrov, A.Bodrov, D.Bolz, A.Borah, J.Bozek, A.Bračko, M.Branchini, P.Browder, T. E.Budano, A.Bussino, S.Campajola, M.Cao, L.Casarosa, G.Cecchi, C.Cerasoli, J.Chang, M. C.Chang, P.Cheaib, R.Cheema, P.Chekelian, V.Chen, Y. Q.Cheon, B. G.Chilikin, K.Chirapatpimol, K.Cho, H. E.Cho, K.Cho, S. J.Choi, S. K.Choudhury, S.Cinabro, D.Cochran, J.Corona, L.Cremaldi, L. M.Cunliffe, S.Czank, T.Das, S.Dattola, F.De La Cruz-Burelo, E.De La Motte, S. A.De Marino, G.De Nardo, G.De Nuccio, M.De Pietro, G.De Sangro, R.Destefanis, M.Dey, S.De Yta-Hernandez, A.Dhamija, R.Di Canto, A.Di Capua, F.Dingfelder, J.DoleŽal, Z.Domínguez Jiménez, I.Dong, T. V.Dorigo, M.Dort, K.Dossett, D.Dreyer, S.Dubey, S.Dujany, G.2023-12-082023-12-082023-09-222023-09-210031-9007https://hdl.handle.net/10919/117149We report the first search for a nonstandard-model resonance decaying into τ pairs in e+e-→μ+μ-τ+τ- events in the 3.6-10 GeV/c2 mass range. We use a 62.8 fb-1 sample of e+e- collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axionlike particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into τ pairs, ranging from 0.7 to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/c2 and for the axionlike particle model over the entire mass range.Pages 121802PrintIn CopyrightBelle II Collaboration5106 Nuclear and Plasma Physics5107 Particle and High Energy Physics4902 Mathematical Physics49 Mathematical Sciences51 Physical Sciences40 EngineeringArticle - Refereedhttps://doi.org/10.1103/PhysRevLett.131.12180213112Piilonen, Leo [0000-0001-6836-0748]378029421079-7114