An improved limit on the axion-photon coupling from the CAST experiment

TL;DR

This paper reports an improved experimental limit on the axion-photon coupling constant using the CERN Axion Solar Telescope, setting the most stringent bounds for certain axion mass ranges and surpassing previous astrophysical constraints.

Contribution

The study provides the most restrictive laboratory-based limit on axion-photon coupling for low axion masses, improving upon previous experimental and astrophysical bounds.

Findings

Set an upper limit of 8.8 x 10^{-11} GeV^{-1} on axion-photon coupling

Achieved the best experimental constraints over a broad axion mass range

Surpassed previous limits from globular-cluster star energy-loss arguments

Abstract

We have searched for solar axions or similar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup with improved conditions in all detectors. From the absence of excess X-rays when the magnet was pointing to the Sun, we set an upper limit on the axion-photon coupling of 8.8 x 10^{-11} GeV^{-1} at 95% CL for m_a <~ 0.02 eV. This result is the best experimental limit over a broad range of axion masses and for m_a <~ 0.02 eV also supersedes the previous limit derived from energy-loss arguments on globular-cluster stars.