Searching for axions with kaon decay at rest

TL;DR

This paper proposes a new method to search for axions produced in kaon decays at rest, using large volume detectors to identify their decay products, and demonstrates that upcoming experiments like JSNS2 can significantly improve sensitivity in the 40-350 MeV mass range.

Contribution

It introduces a novel search strategy for hadronically coupled axions via kaon decay at rest and evaluates the potential sensitivity of upcoming experiments like JSNS2.

Findings

JSNS2 can achieve world-leading sensitivity to axions in the 40-350 MeV mass range.

Recast of MicroBooNE data constrains axion parameter space.

The proposed method is feasible with existing and near-term detectors.

Abstract

We describe a novel search strategy for axions (or hadronically coupled axion-like particles) in the mass range of $m_a \lesssim 350\,{\rm MeV}$. The search relies on kaon decay at rest, which produces a mono-energetic signal in a large volume detector (e.g.\ a tank of liquid scintillator) from axion decays $a\rightarrow \gamma\gamma$ or $a\rightarrow e^+e^-$. The decay modes $K^+\to \pi^+ a$ and $a \to \gamma \gamma$ are induced by the axion's coupling to gluons, which is generic to any model which addresses the strong CP problem. We recast a recent search from MicroBooNE for $e^+e^-$ pairs, and study prospects at JSNS$^2$ and other near-term facilities. We find that JSNS$^2$ will have world-leading sensitivity to hadronically coupled axions in the mass range of $40\,\mathrm{MeV} \lesssim m_a \lesssim 350\,\mathrm{MeV}$.