$B\to K^{(*)}\nu\bar\nu$ decays in the Standard Model and beyond

TL;DR

This paper provides precise Standard Model predictions for rare B decays involving neutrinos, explores potential new physics effects using effective operators, and constrains various beyond Standard Model scenarios through experimental data correlations.

Contribution

It offers the most accurate SM predictions for $B o K^{(*)} uar u$ decays and analyzes new physics models using a model-independent effective theory approach.

Findings

SM branching ratio predictions are more precise than previous estimates.

Constraints on NP effects are derived from experimental data on related decays.

Correlations among observables provide powerful tests for specific NP models.

Abstract

We present an analysis of the rare exclusive $B$ decays $B\to K\nu\bar\nu$ and $B\to K^{*}\nu\bar\nu$ within the Standard Model (SM), in a model-independent manner, and in a number of new physics (NP) models. Combining new form factor determinations from lattice QCD with light-cone sum rule results and including complete two-loop electroweak corrections to the SM Wilson coefficient, we obtain the SM predictions $\text{BR}(B^+\to K^+\nu\bar\nu) = (4.0 \pm 0.5) \times 10^{-6}$ and $\text{BR}(B^0\to K^{* 0}\nu\bar\nu) = (9.2\pm1.0) \times 10^{-6}$, more precise and more robust than previous estimates. Beyond the SM, we make use of an effective theory with dimension-six operators invariant under the SM gauge symmetries to relate NP effects in $b\to s\nu\bar\nu$ transitions to $b\to s\ell^+\ell^-$ transitions and use the wealth of experimental data on $B\to K^{(*)}\ell^+\ell^-$ and related modes to constrain NP effects in $B\to K^{(*)}\nu\bar\nu$. We then consider several specific NP models, including $Z'$ models, the MSSM, models with partial compositeness, and leptoquark models, demonstrating that the correlations between $b\to s\nu\bar\nu$ observables among themselves and with $B_s\to\mu^+\mu^-$ and $b\to s\ell^+\ell^-$ transitions offer powerful tests of NP with new right-handed couplings and non-MFV interactions.