Catalog · Beauty · B023

B023 $\mathcal{B}(B\to K^*\nu\bar{\nu})$

Invisible rare B $ \to $ K*(892) $\nu \bar{\nu}$ decays

Status REVIEWED VERIFIED High Code: NO Priority Low

PDG / equivalent values

Observable	Value	Year	Experiment / source	Provenance
Combined BR(B $ \to K* \nu \bar{\nu}$)	<2.7e-5 branching fraction	2017	Belle2017:B023:combined_vector_limit	source ↑
SM BR(B0 $ \to $ K*(892)0 $\nu \bar{\nu}$)	9.2e-6 branching fraction	2015	Buras2015:B023:sm_b0_kstar0_nunu	source ↑

Why this constrains the RS scan

These modes probe the $\Delta B=1$ FCNC transition $b\to s\nu\bar{\nu}$. In RS/anarchic-flavor models they are sensitive to flavor-changing $Z$, heavy electroweak-gauge, or other neutral-current couplings generated after fermion localization and mass-basis rotation. They are complementary to $B_s$ mixing because the final state tests a semileptonic neutral current, not a $\Delta F=2$ four-quark amplitude, and the $K^*$ final state can also separate left- and right-handed short-distance structures through polarization.

What's changed since the original paper

The CFW 2008 baseline predates all current $B\to K^*\nu\bar{\nu}$ limits. (CsakiFalkowskiWeiler2008:CompositeFlavor). Belle's 2013 full-$\Upsilon(4S)$ hadronic-tag analysis set the charged-mode limit $B^+\to K^{*+}\nu\bar{\nu} <4.0\times10^{-5}$ (Belle2013:BHnunuHadronic). BaBar's 2013 hadronic-tag result found no significant excess and remains useful as superseded input history (BaBar2013:BKstarNunu). Belle's 2017 semileptonic-tag search improved the neutral mode to $<1.8\times10^{-5}$ and quoted a combined vector limit of $<2.7\times10^{-5}$ (Belle2017:BHnunuSemileptonic). Buras--Girrbach-Noe--Niehoff--Straub 2015 updated the SM treatment using form factors and electroweak corrections, quoting $\mathcal{B}(B^0\to K^{*0}\nu\bar{\nu})=(9.2\pm1.0)\times10^{-6}$, and framed the right-handed-current observables used in later new-physics studies (BurasGirrbachNoeNiehoffStraub2015:BKstarNunu).

Validity and model dependence

Experimentally this is a clean missing-energy upper limit, but it is not a drop-in bound for the present quark scan. A production constraint needs the $b\to s\nu\bar{\nu}$ weak Hamiltonian, $B\to K^*$ form factors, treatment of right-handed currents and polarization, and either an experimental likelihood or a conservative reinterpretation of the published upper limits.

Code coverage in this repo

NO. Targeted greps over quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, and tests/ found no $B\to K^*\nu\bar{\nu}$, $b\to s\nu\bar{\nu}$, or invisible-$B$ implementation. The modern phenomenology surface is limited to $\epsilon_K$, $K$, $B_d$, $B_s$, and $D^0$ at quarkConstraints/modern/phenomenology.py:23. The legacy default inputs are $\Delta F=2$ at quarkConstraints/deltaf2.py:209, with $B_d$ and $B_s$ mixing evaluators at quarkConstraints/deltaf2.py:903 and quarkConstraints/deltaf2.py:922. The only live lepton-flavor routine found is $\mu\to e\gamma$ at flavorConstraints/muToEGamma.py:75.

Linked evidence (opens GitHub blob at flavor-catalog-website/2026q2):

Implementation difficulty

HIGH. Implementing B023 requires a new $\Delta B=1$ $b\to s\nu\bar{\nu}$ operator basis, RS matching for neutral-current left- and right-handed coefficients, $B\to K^*$ form-factor and polarization treatment, and an upper-limit likelihood or validated CL reinterpretation.

Key references

PDG2025:B0KstarNunu, PDG2025:BpKstarNunu, HFLAV2025Dec:B0KstarNunu, HFLAV2025Dec:BpKstarNunu, Belle2017:BHnunuSemileptonic, Belle2013:BHnunuHadronic, BaBar2013:BKstarNunu, BurasGirrbachNoeNiehoffStraub2015:BKstarNunu, and CsakiFalkowskiWeiler2008:CompositeFlavor.

fallback_value_uncertainty B0 -> K*(892)0 nu nubar = 1.8e-5 90%

AMBIGUOUS

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fallback_value_uncertainty B+ -> K*(892)+ nu nubar = 4e-5 90%

AMBIGUOUS

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L14:    "description": "G(B+ --> K*(892)+ nu nubar)/G(total)",
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fallback_value_uncertainty Combined BR(B -> K* nu nubar) = 2.7e-5 90% CL

RESOLVED

Match snapshot line 24

L21: Source-extracted combined-limit text from arXiv TeX source:
L22: The analysis combines charged and neutral modes by adding negative log
L23: likelihoods, scaling neutral modes by tau(B+)/tau(B0), and obtains
L24: B(B -> K* nu nubar) < 2.7 x 10^{-5} at 90% C.L.

fallback_value_uncertainty SM BR(B0 -> K*(892)0 nu nubar) = (9.2 +- 1)e-6

RESOLVED

Match snapshot line 17

L14: The paper combines lattice-QCD and light-cone-sum-rule form factors with
L15: complete two-loop electroweak corrections to obtain
L16: BR(B+ -> K+ nu nubar) = (4.0 +/- 0.5) x 10^{-6} and
L17: BR(B0 -> K*0 nu nubar) = (9.2 +/- 1.0) x 10^{-6}.
L18: 
L19: Source-extracted model-dependence note:
L20: The analysis relates new-physics effects in b -> s nu nubar to b -> s l+l-