Decoding the $B$ → $Kvv$ excess at Belle II: Kinematics, operators, and masses

An excess in the branching fraction for B+ → K+⁢vv recently measured at Belle II may be a hint of new physics. We perform thorough likelihood analyses for different new physics scenarios such as B → K⁢X with a new invisible particle χ, or B → K⁢χχ through a scalar, vector, or tensor current with χ b...

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Bibliographic Details
Published in:Physical review. D 2024-06, Vol.109 (11)
Main Authors: Fridell, Kåre, Ghosh, Mitrajyoti, Okui, Takemichi, Tobioka, Kohsaku
Format: Article
Language:English
Subjects:
Bottom mesons
Dark matter
Effective field theory
Kaons
Leptonic, semileptonic & radiative decays
Neutrinos
Rare decays
Signatures with missing energy
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Summary:An excess in the branching fraction for B+ → K+⁢vv recently measured at Belle II may be a hint of new physics. We perform thorough likelihood analyses for different new physics scenarios such as B → K⁢X with a new invisible particle χ, or B → K⁢χχ through a scalar, vector, or tensor current with χ being a new invisible particle or a neutrino. We find that vector-current three-body decay with mχ ≃ 0.6 GeV—which may be dark matter—is most favored, while two-body decay with mχ ≃ 2 GeV is also competitive. The best-fit branching fractions for the scalar and tensor cases are a few times larger than for the two-body and vector cases. Past BABAR measurements provide further discrimination, although the best-fit parameters stay similar.
ISSN:2470-0010