New perspective in searching for axion-like particles from flavor physics

TL;DR

This paper introduces a novel approach to searching for axion-like particles (ALPs) using flavor physics measurements, focusing on specific B meson decay processes and the muon's anomalous magnetic moment to explore previously inaccessible parameter regions.

Contribution

It proposes new flavor physics observables as complementary probes for ALPs, especially at the pion mass scale, to fill existing gaps in the parameter space.

Findings

Enhanced experimental sensitivity at the pion mass scale for ALP detection.

Identification of 'sweetest' spots where ALP signals are maximized.

Potential to cover previously unexplored ALP parameter regions.

Abstract

We propose new perspective in searching for axion-like particles (ALPs) from quark and lepton flavor physics: measurements of the time-dependent CP asymmetry in $B^0 \to K_S^0 \pi^0 \gamma$ and the branching ratio of $B_s \to e^\pm \mu^\mp$ decay possess, along with the anomalous magnetic moment of muon. In the mass range of sub-GeV, accessible by the flavorful ALPs search, the experimental sensitivity for these flavor observables reaches the maximum at around the pion mass scale (called the {\it sweetest} spots), where a couple of loopholes (unexplored regions) for the ALP parameter space have heretofore been present, because of an unavoidable contamination with pion background events. The proposed complementary probes can precisely determine the ALP coupling to photon at these {\it sweetest} spots/loopholes, and will significantly help cover whole parameter spaces in the ALP search including the present loopholes in the future.