Search for solar axions with mass around 1 eV using coherent conversion of axions into photons

A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3-m long 4 T superconducting magnet, a gas container to hold dispersion-matching gas, PIN-photodiode X-ray detectors, and a telescope mount mechanism to track the sun. A mass region around ma=1 eV was newly explored. From the absence of any evidence, analysis sets a limit on axion–photon coupling constant to be gaγγ<5.6–13.4×10−10 GeV−1 for the axion mass of 0.84<ma<1.00 eV at 95% confidence level. It is the first result to search for the axion in the gaγγ–ma parameter region of the preferred axion models with a magnetic helioscope.