Search for solar hadronic axions produced by a bremsstrahlung-like process

TL;DR

This study searches for solar hadronic axions produced via bremsstrahlung-like processes, using an HPGe detector to observe axioelectric interactions, setting an upper limit on axion mass and focusing on axion-electron coupling.

Contribution

It provides the first experimental upper limit on solar hadronic axion mass based on axion-electron coupling without relying on uncertain axion-nucleon coupling estimates.

Findings

Upper limit on axion mass: m_a < 334 eV at 95% C.L.

Experimental approach based on axion-electron coupling.

No detection of axions in the searched parameter space.

Abstract

We have searched for hadronic axions which may be produced in the Sun by a bremsstrahlung-like process, and observed in the HPGe detector by an axioelectric effect. A conservative upper limit on the hadronic axion mass m_a < 334 eV at 95% C.L. is obtained. Our experimental approach is based on the axion-electron coupling and it does not include the axion-nucleon coupling, which suffers from the large uncertainties related to the estimation of the flavor-singlet axial-vector matrix element.