Search for an Axion-Like Particle in $B\rightarrow K^{(*)} a (\rightarrow\gamma\gamma)$ Decays at Belle

TL;DR

This study searches for axion-like particles in B meson decays at Belle, setting new upper limits on their coupling to W bosons across a broad mass range, with no significant signals observed.

Contribution

First search for axion-like particles in B decays at Belle, providing improved constraints on their coupling to W bosons over previous experiments.

Findings

No significant axion-like particle signals detected.

Established upper limits on coupling constants, improving previous bounds.

Extended mass range for axion-like particle searches.

Abstract

We report a search for an axion-like particle $a$ in $B\rightarrow K^{(*)} a (\rightarrow\gamma\gamma)$ decays using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. The search is based on a $711 \mathrm{fb^{-1}}$ data sample collected at the $\Upsilon 4S$ resonance energy, corresponding to a sample of $772\times10^6$ $\Upsilon 4S$ events. In this study, we search for the decay of the axion-like particle into a pair of photons, $a \rightarrow \gamma\gamma$. We scan the two-photon invariant mass in the range $0.16\ \mathrm{GeV/}c^2-4.50\ \mathrm{GeV}/c^2$ for the $K$ modes and $0.16\ \mathrm{GeV/}c^2-4.20\ \mathrm{GeV}/c^2$ for the $K^{*}$ modes. No significant signal is observed in any of the modes, and 90\% confidence level upper limits are established on the coupling to the $W$ boson, $g_aW$, as a function of $a$ mass. The limits range from $3 \times 10^{-6} \mathrm{GeV}^{-1}$ to $3 \times 10^{-5} \mathrm{GeV}^{-1}$, improving the current constraints on $g_aW$ by a factor of two over the most stringent previous experimental results.