Search for $B^0 \to K^{*0}\tau^+\tau^-$ decays at the Belle II experimentAdachi, Ichiro (Avtor) Adamczyk, Karol (Avtor) Bračko, Marko (Avtor) Korpar, Samo (Avtor) Križan, Peter (Avtor) Pestotnik, Rok (Avtor) Podobnik, Tomaž (Avtor) Šantelj, Luka (Avtor) Starič, Marko (Avtor) Zhukova, Valentina (Avtor) experimental physicsphysics of elementary particlesparticle decaysWe present a search for the rare flavor-changing neutral-current decay $B^0 \to K^{\ast 0}\tau^+\tau^-$ with data collected by the Belle II experiment at the SuperKEKB electron-positron collider. The analysis uses a 365  fb$^{−1}$ data sample recorded at the center-of-mass energy of the $\Upsilon(4⁢S)$ resonance. One of the $B$ mesons produced in the $\Upsilon(4S)\to B^0 \bar{B}^0$ process is fully reconstructed in a hadronic decay mode, while its companion $B$ meson is required to decay into a $K^{\ast 0}$ and two $\tau$ leptons of opposite charge. The $\tau$ leptons are reconstructed in final states with a single electron, muon, charged pion or charged $\rho$ meson, and additional neutrinos. We set an upper limit on the branching fraction of $\mathcal{B}(B^0 \to K^{\ast 0} \tau^+ \tau^-) < 1.8 \times 10^{-3}$ at the 90% confidence level, which is the most stringent constraint reported to date.20252026-01-30 10:33:03Članek v reviji178833sl