Decoding the $B\to K\nu \nu$ excess at Belle II: kinematics, operators, and masses

Abstract

An excess in the branching fraction for $B^{+}\to K^{+}\nu \nu$ recently measured at Belle II may be a hint of new physics. We perform thorough likelihood analyses for different new physics scenarios such as $B\to KX$ with a new invisible particle $X$, or $B\to K\chi \chi$ through a scalar, vector, or tensor current with $\chi$ being a new invisible particle or a neutrino. We find that vector-current 3-body decay with $m_X\simeq 0.6$ GeV - which may be dark matter - is most favored, while 2-body decay with $m_X\simeq 2$ GeV is also competitive. The best-fit branching fractions for the scalar and tensor cases are a few times larger than for the 2-body and vector cases. Past BaBar measurements provide further discrimination, although the best-fit parameters stay similar.

7 pages, 6 figures, matches published version

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Cited by in corpus (20)

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• Impact of new invisible particles on $B\to K^{(\ast )}{E}_{\mathrm{miss}}$ observables
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• $B\to K+$invisible, dark matter, and $CP$ violation in hyperon decays
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• Analysis of $q_{\mathrm{rec}}^2$-distribution for $B\to K{M}_X$ and $B\to K^{\ast }{M}_X$ decays in a scalar-mediator dark-matter scenario
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• Resonant ALP-Portal Dark Matter Annihilation as a Solution to the $B^{\pm }\to K^{\pm }\nu \bar{\nu }$ Excess
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• Dark Matter emission at Belle II and NA62 in Minimal Flavor Violation framework
• Feasibility Study of Lepton Number Violation in Rare $B$ and $K$ Meson Decays
• Characterizing Dark Bosons at Chiral Belle
• Model-agnostic likelihood for the reinterpretation of the $B^{+}\to K^{+}\nu \bar{\nu }$ measurement at Belle II
• Belle II Constraints on the Non-Minimal Universal Extra Dimensional Model
• Analysis of $B\to K{M}_X$ and $B\to K^{\ast }{M}_X$ decays in scalar- and vector-mediator dark-matter scenarios
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