Search for Lepton-Flavor-Violating Decay Modes B0 → KS0 τ±ℓ∓ with Hadronic B Tagging at Belle and Belle II

I Adachi; K Adamczyk; L Aggarwal; H Ahmed; H Aihara; N Akopov; M Alhakami; A Aloisio; N Althubiti; NA Ky; DM Asner; H Atmacan; V Aushev; M Aversano; R Ayad; V Babu; H Bae; NK Baghel; S Bahinipati; P Bambade; S Banerjee; S Bansal; M Barrett; M Bartl; J Baudot; A Baur; A Beaubien; F Becherer; J Becker; JV Bennett; FU Bernlochner; V Bertacchi; M Bertemes; E Bertholet; M Bessner; S Bettarini; V Bhardwaj; B Bhuyan; F Bianchi; D Biswas; A Bobrov; D Bodrov; A Bolz; A Boschetti; A Bozek; M Bračko; P Branchini; RA Briere; TE Browder; A Budano; S Bussino; Q Campagna; M Campajola; L Cao; G Casarosa; C Cecchi; J Cerasoli; MC Chang; P Chang; R Cheaib; P Cheema; BG Cheon; K Chilikin; K Chirapatpimol; HE Cho; K Cho; SJ Cho; SK Choi; S Choudhury; J Cochran; L Corona; JX Cui; E De La Cruz-Burelo; SA De La Motte; G De Marino; G De Nardo; G De Pietro; R De Sangro; M Destefanis; S Dey; R Dhamija; A Di Canto; F Di Capua; J Dingfelder; Z DoleŽal; ID Jiménez; TV Dong; X Dong; M Dorigo; D Dossett; S Dubey; K Dugic; G Dujany; P Ecker; P Feichtinger; T Ferber; T Fillinger; C Finck; G Finocchiaro; A Fodor

Journal article

Search for Lepton-Flavor-Violating Decay Modes B0 → KS0 τ±ℓ∓ with Hadronic B Tagging at Belle and Belle II

I Adachi, K Adamczyk, L Aggarwal, H Ahmed, H Aihara, N Akopov, M Alhakami, A Aloisio, N Althubiti, NA Ky, DM Asner, H Atmacan, V Aushev, M Aversano, R Ayad, V Babu, H Bae, NK Baghel, S Bahinipati, P Bambade Show all

Physical Review Letters | American Physical Society (APS) | Published : 2025

DOI: 10.1103/yzvh-v3hm

Abstract

We present the first search for the lepton-flavor-violating decay modes B0→KS0τ±ℓ∓ (ℓ=μ,e) using the 711 and 365 fb-1 data samples recorded by the Belle and Belle II detectors, respectively. We use a hadronic B-tagging technique to fully reconstruct a B meson and search for signal decays in the system recoiling against the tagged meson, considering τ decays to either light leptons, one charged hadron, or one charged hadron and a neutral pion. We find no evidence for B0→KS0τ±ℓ∓ decays and set 90% confidence level upper limits on the branching fractions in the range of [0.8,3.6]×10-5.