Model-agnostic likelihood for the reinterpretation of the $B^+ \to K^+\nu\bar{\nu}$ measurement at Belle II

Abumusabh, M. (author), Borah, Jyotirmoi (author), Bračko, Marko (author), Korpar, Samo (author), Križan, Peter (author), Lozar, Andrej (author), Pestotnik, Rok (author), Podobnik, Tomaž (author), Šantelj, Luka (author), Starič, Marko (author)

We recently measured the branching fraction of the $B^+ \to K^+\nu\bar{\nu}$⁢ decay using 362  fb$^{-1}$ of on-resonance $e^+e^-$ collision data under the assumption of Standard Model kinematics, providing the first evidence for this decay. To facilitate future reinterpretations and maximize the scientific impact of this measurement, we publicly release the full analysis likelihood along with all necessary material required for reinterpretation under arbitrary theoretical models sensitive to this measurement. In this work, we demonstrate how the measurement can be reinterpreted within the framework of the weak effective theory. Using a kinematic reweighting technique in combination with the published likelihood, we derive marginal posterior distributions for the Wilson coefficients, construct credible intervals, and assess the goodness of fit to the Belle II data. For the weak effective theory Wilson coefficients, the posterior mode of the magnitudes |$C_{\mathrm{VL}}+C_{\mathrm{VR}}$|, |$C_{\mathrm{SL}}+C_{\mathrm{SR}}$|, and |$C_{\mathrm{TL}}$| corresponds to the point (11.3, 0.0, 8.2). The respective 95% credible intervals are [1.9, 16.2], [0.0, 15.4], and [0.0, 11.2].

• Language: English
• Keywords: experimental nuclear physics, physics of elementary particles
• 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. 092016-1-092016-10
• Numbering: Vol. 112, iss. 9
• PID: 20.500.12556/RUL-178836
• UDC: 539.1
• ISSN on article: 2470-0010
• DOI: 10.1103/pr66-sd36
• COBISS.SI-ID: 266634243
• Publication date in RUL: 30.01.2026

Record is a part of a journal

• Title: Physical review
• Shortened title: Phys. rev., D
• Publisher: American Physical Society
• ISSN: 2470-0010
• COBISS.SI-ID: 29757223

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 jedrska fizika, fizika osnovnih delcev

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: J1-50010
• Name: Eksperimentalno preverjanje leptonske univerzalnosti in izboljšava metod identifikacije delcev pri eksperimentu Belle II

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