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Explaining Belle data on $B \to K^{(*)} ν \bar{ν}$ decays via dark $Z$ resonances

T. M. Aliev ¹, A. Elpe ¹, L. Selbuz ², and I. Turan ¹

¹Department of Physics, Middle East Technical University, Ankara 06800, Turkey
²Department of Engineering Physics, Ankara University, TR06100 Ankara, Turkey

Phys. Rev. D 112, 015025 – Published 25 July, 2025

DOI: https://doi.org/10.1103/6j6r-9vsl

Abstract

The Belle II Collaboration reported the first measurement on $Br (B^{+} \to K^{+} ν \bar{ν})$ , which lies $2.7 σ$ away from the Standard Model expectation. This result may be manifestation of new physics beyond the Standard Model. In present work, motivated by the Belle II measurement, we investigate the effect of a dark photon/dark $Z$ on the rare $B$ meson decay $B^{+} \to K^{+} ν \bar{ν}$ and show that the $Br (B^{+} \to K^{+} ν \bar{ν})$ excess from Belle II over the Standard Model expectation explained by the appearance of the dark $Z$ especially in resonances. We also derive constraints on various parameters of the two-Higgs-doublet model extended with a dark Abelian gauge group, in light of the measurement of the $Br (B^{+} \to K^{+} ν \bar{ν})$ by the Belle-II Collaboration as well as the upper bound on $Br (B^{0} \to K^{* 0} ν \bar{ν})$ decay, set by the Belle data. Our results indicate that there exists a common region where both experimental results are satisfied for a dark $Z$ mass around 4.5 GeV with suitable values of the other parameters.

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Phys. Rev. D 112, 015025– Published 25 July, 2025

Vol. 112, Iss. 1 — 1 July 2025

Received 5 April 2025
Accepted 1 July 2025

DOI: https://doi.org/10.1103/6j6r-9vsl

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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Explaining Belle data on $B \to K^{(*)} ν \bar{ν}$ decays via dark $Z$ resonances

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Explaining Belle data on B→K(*)νν¯ decays via dark Z resonances

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Explaining Belle data on $B \to K^{(*)} ν \bar{ν}$ decays via dark $Z$ resonances