Model-independent bounds on light pseudoscalars from rare B-meson decays

TL;DR

This paper establishes model-independent bounds on light pseudoscalars, like axion-like particles, from rare B-meson decay experiments, updating and comparing experimental sensitivities and providing new constraints.

Contribution

It introduces a model-independent approach for constraining light spin-0 bosons in B decays, updating bounds from existing experiments and analyzing their complementarity.

Findings

Updated bounds from LHCb, CHARM, NA62, and SHiP experiments.

Provided upper limits on B→K A and A→μ+μ− branching ratios.

Demonstrated the complementarity of different experimental geometries.

Abstract

New light pseudoscalars, such as axion-like particles, appear in many well-motivated extensions of the Standard Model and provide an exciting target for present and future experiments. We study the experimental sensitivity for such particles by revising the CHARM exclusion contour, updating bounds from LHCb and presenting prospects for NA62 and SHiP. We first consider a simplified model of a light pseudoscalar $A$ and then propose a model-independent approach applicable to any spin-0 boson light enough to be produced in B-meson decays. As illustration, we provide upper bounds on $\text{BR}(B \to K\,A) \times \text{BR}(A \to \mu^+\mu^-)$ as a function of the boson lifetime and mass for models that satisfy minimal flavour violation. Our results demonstrate the important complementarity between different experiments resulting from their different geometries.