Search for $B^0 \to K^{*0}\tau^+\tau^-$ decays at the Belle II experiment

Adachi, Ichiro (author), Adamczyk, Karol (author), Bračko, Marko (author), Korpar, Samo (author), Križan, Peter (author), Pestotnik, Rok (author), Podobnik, Tomaž (author), Šantelj, Luka (author), Starič, Marko (author), Zhukova, Valentina (author)

We 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.

• Language: English
• Keywords: experimental physics, physics of elementary particles, particle decays
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: Str. 151801-1-151801-8
• Numbering: Vol. 135, iss. 15
• PID: 20.500.12556/RUL-178833
• UDC: 539.1
• ISSN on article: 0031-9007
• DOI: 10.1103/v1q3-9dy8
• COBISS.SI-ID: 266682627
• Publication date in RUL: 30.01.2026

Record is a part of a journal

• Title: Physical review letters
• Shortened title: Phys. rev. lett.
• Publisher: American Physical Society
• ISSN: 0031-9007
• COBISS.SI-ID: 1282575

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: eksperimentalna fizika, fizika osnovnih delcev, razpadi delcev

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: J1-9124
• Name: Napredne metode za identifikacijo hadronov pri eksperimentu Belle II

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P1-0135
• Name: Eksperimentalna fizika osnovnih delcev