Search for lepton-flavor-violating decay modes $B^0 \to K^0_S \tau^{\pm}\ell^{\mp}$ with hadronic B tagging at Belle and Belle IIAdachi, Ichiro (Avtor) Adamczyk, Karol (Avtor) Bračko, Marko (Avtor) Korpar, Samo (Avtor) Križan, Peter (Avtor) Pestotnik, Rok (Avtor) Podobnik, Tomaž (Avtor) Prudiiev, Ihor (Avtor) Šantelj, Luka (Avtor) Starič, Marko (Avtor) Zhukova, Valentina (Avtor) experimental physicsphysics of elementary particlesparticle decaysWe present the first search for the lepton-flavor-violating decay modes $B^0 \to K^0_S\tau^{\pm}\ell^{\mp}(\ell = \mu, e)$ 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 $\tau$ decays to either light leptons, one charged hadron, or one charged hadron and a neutral pion. We find no evidence for $B^0 \to K^0_S\tau^{\pm}\ell^{\mp}$ decays and set 90 % confidence level upper limits on the branching fractions in the range of [0.8,3.6] × 10$^{-5}$. 20252026-01-30 10:01:35Članek v reviji178825UDK: 539.1ISSN pri članku: 0031-9007DOI: 10.1103/yzvh-v3hmCOBISS_ID: 266690819sl