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Deciphering the Belle II data on $B\to K \nu \bar\nu$ decay in the (dark) SMEFT with minimal flavour violation

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arxiv 2402.19208 v2 pith:BZR76LB4 submitted 2024-02-29 hep-ph hep-ex

classification hep-phhep-ex
keywords belleoperatorsdarkdecayssmeftdatafirstflavour
verification ladder T0 review T1 audit T2 compute T3 formal

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abstract

Recently, the Belle II collaboration announced the first measurement of $\mathcal B(B^+\to K^+\nu\bar\nu)$, which is found to be about $2.7\sigma$ higher than the SM prediction. We decipher the data with two new physics scenarios: the underlying $b\to s \nu\bar\nu$ transition is, besides the SM contribution, further affected by heavy new mediators that are much heavier than the EW scale, or amended by an additional decay channel with undetected light final states like dark matter or axion-like particles. These two scenarios can be most conveniently analyzed in the SMEFT and the dark SMEFT (DSMEFT) framework, respectively. We consider the flavour structures of the resulting effective operators to be either generic or satisfy the minimal flavour violation (MFV) hypothesis, both for the quark and lepton sectors. In the first scenario, once the MFV is assumed, only one SM-like low-energy effective operator induced by the SMEFT dim-6 operators can account for the Belle II excess, the parameter space of which is, however, excluded by the Belle upper bound on $\mathcal B(B^0\to K^{*0}\nu\bar\nu)$. In the second scenario, it is found that the Belle II excess can be accommodated by 22 of the DSMEFT operators involving one or two scalar, fermionic, or vector dark matters as well as ALPs. These operators also receive dominant constraints from the $B^0\to K^{*0}+$inv and $B_s\to$inv decays. In the MFV hypothesis, the number of viable operators is reduced to 14, and the $B^+\to\pi^+ +$inv and $K^+\to\pi^++$inv decays start to put further constraints. Within the parameter space allowed by all the current experimental data, the $q^2$ distributions (and $F_L$) of the $B\to K^{(*)}+$inv decays are studied for each viable operator. In addition, we, for the first time, calculate systematically the longitudinal polarization fraction $F_L$ of $K^*$ in the $B\to K^*+$inv decays within the DLEFT.

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Forward citations

Cited by 12 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Radiative generation of chiral vector operators in $b\to s \nu\bar{\nu}$ transition

    hep-ph 2026-01 conditional novelty 6.0 of 10

    Minimal one-loop models that generate both chiral vector operators for b→sνν̄ are systematically classified but cannot quantitatively explain the Belle II anomaly.

  2. Gauged $\tau$-lepton chiral currents and $B \to K^{(*)} E_{\rm miss}$

    hep-ph 2025-05 conditional novelty 6.0 of 10

    Gauging chiral tau lepton number with a light X boson of mass about 2.1 GeV explains the Belle II B to K missing-energy excess and survives existing bounds.

  3. $B\to K{+}$invisible, dark matter, and $CP$ violation in hyperon decays

    hep-ph 2025-02 conditional novelty 6.0 of 10

    In a two-Higgs-doublet plus scalar dark matter model, hyperon decay CP asymmetries can reach parts in a thousand, far above the standard model, while still satisfying kaon and dark matter constraints.

  4. New Strategies for New Physics Search with $\Lambda_b \to \Lambda \nu \bar\nu$ Decays

    hep-ph 2025-01 conditional novelty 6.0 of 10

    For longitudinally polarized Lambda_b at future Z-pole machines, Lambda_b -> Lambda nu nubar has a forward-backward asymmetry that is independent of new physics at its zero crossing and complements the branching ratio...

  5. Are the new particles heavy or light in $b \to s E_{\mathrm{miss}}$?

    hep-ph 2024-12 conditional novelty 6.0 of 10

    The K* longitudinal polarization fraction separates heavy NP, light vector, and ALP explanations of the Belle-II B+ to K+ missing-energy excess, while the Lambda_b to Lambda polarization tags operator chirality.

  6. Flavor Violations in $B$-Mesons within Non-Minimal SU(5)

    hep-ph 2024-12 conditional novelty 6.0 of 10

    A non-minimal SU(5) model with R2 leptoquark and S6 diquark is fitted to B-decay anomalies in b→cτν, B→Kπ, and B→Kνν, but the benchmark B→Kνν rate rises only about 3.5% above the Standard Model.

  7. On the Interplay of Constraints from $B_s$, $D$, and $K$ Meson Mixing in $Z^\prime$ Models with Implications for $b\to s \nu\bar\nu$ Transitions

    hep-ph 2024-12 conditional novelty 6.0 of 10

    In Z' models with suppressed B_s mixing, SU(2)L and SMEFT RG correlations tie the B_s, D, and K sectors together and predict B to K(K*) nu nu enhancements of up to 20% when b to s mu mu rates are suppressed.

  8. Precision calculations of $B\to K^*$ form factors from SCET sum rules beyond leading-power contributions

    hep-ph 2024-12 conditional novelty 6.0 of 10

    New subleading-power corrections to B to K* form factors from SCET sum rules yield SM branching fractions BR(Bbar0 to Kbar*0 nu nubar)=8.09(96)e-6 and F_L=0.44(4).

  9. A Unified Dark Matter Explanation for $\boldsymbol{B^+ \!\to K^+\nu\bar{\nu}}$ and the Super-Kamiokande Antineutrino Excess

    hep-ph 2026-07 conditional novelty 5.0 of 10

    A UV-complete complex scalar DM model under gauged U(1)Lμ−Lτ accommodates the SK antineutrino excess, the Belle II B+→K+νν̄ excess, and the DM relic density with one light dark sector.

  10. Probing ALP couplings to electroweak gauge bosons

    hep-ph 2025-01 conditional novelty 5.0 of 10

    Rare two-body meson decays give the strongest current bounds on the ALP-W coupling for light ALPs, with Z-boson decays and future lepton colliders extending the reach to heavier masses.

  11. Probing $B^+ \to K^+$ semi-leptonic FCNC decay with new physics effects under PQCD approach

    hep-ph 2024-12 conditional novelty 5.0 of 10

    An improved PQCD plus lattice calculation of B to K semileptonic FCNC form factors confirms a 2.7 sigma excess in B+ to K+ nu nubar and a deficit in B+ to K+ l+ l-, and rules out single-leptoquark explanations using B...

  12. The rare decay $B^+ \to K^+\ell^+\ell^-(\nu\bar{\nu})$ under the QCD sum rules approach

    hep-ph 2024-11 conditional novelty 4.0 of 10

    A QCD light-cone sum-rule calculation with the authors' kaon distribution amplitudes predicts B(B+ to K+ nu nubar) = 4.14 x 10^-6 and B(B+ to K+ l+l-) around 6.6 x 10^-7, consistent with other SM estimates.

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