Search for 14.4 keV solar axions emitted in the M1-transition of 57Fe nuclei with CAST

TL;DR

This study searched for 14.4 keV solar axions emitted from 57Fe nuclei using the CAST experiment, setting new constraints on axion-photon and axion-nucleon couplings based on the absence of detected signals.

Contribution

It provides the first model-independent experimental limits on axion couplings from solar 57Fe nuclear transitions using the CAST setup.

Findings

No excess X-ray signal detected from the Sun.

Set upper limits on axion coupling constants.

Constraints improve previous bounds for low-mass axions.

Abstract

We have searched for 14.4 keV solar axions or more general axion-like particles (ALPs), that may be emitted in the M1 nuclear transition of 57Fe, by using the axion-to-photon conversion in the CERN Axion Solar Telescope (CAST) with evacuated magnet bores (Phase I). From the absence of excess of the monoenergetic X-rays when the magnet was pointing to the Sun, we set model-independent constraints on the coupling constants of pseudoscalar particles that couple to two photons and to a nucleon g_{a\gamma} |-1.19 g_{aN}^{0}+g_{aN}^{3}|<1.36\times 10^{-16} GeV^{-1} for m_{a}<0.03 eV at the 95% confidence level.