Search for 𝐵⁰→𝐾*⁰𝜏⁺⁢𝜏⁻ Decays at the Belle II Experiment

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2025

Authors

Adachi, I.
Adamczyk, K.
Aggarwal, L.
Ahmed, H.
Aihara, H.
Akopov, N.
Alhakami, M.
Aloisio, A.
Althubiti, N.
Angelsmark, M.

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Physical Review Letters, 2025; 135(15):151801-1-151801-8

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Belle II Collaboration

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Abstract

We present a search for the rare flavor-changing neutral-current decay 𝐵0→𝐾*0⁢𝜏+⁢𝜏− 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 ϒ⁡(4⁢𝑆) resonance. One of the 𝐵 mesons produced in the ϒ⁡(4⁢𝑆)→𝐵0⁢ ¯ 𝐵 0 process is fully reconstructed in a hadronic decay mode, while its companion 𝐵 meson is required to decay into a 𝐾*0 and two 𝜏 leptons of opposite charge. The 𝜏 leptons are reconstructed in final states with a single electron, muon, charged pion or charged 𝜌 meson, and additional neutrinos. We set an upper limit on the branching fraction of ℬ⁡(𝐵0→𝐾*0⁢𝜏+⁢𝜏−)<1.8×10−3 at the 90% confidence level, which is the most stringent constraint reported to date.

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Published 6 October 2025

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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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