A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3 { m } \times 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 .
In the past measurements , axion mass up to 0.27 eV have been scanned with this helioscope .
It has been upgraded to handle dispersion-matching gas ( ^ { 4 } He ) of higher density to explore higher mass region .
From December 2007 through April 2008 , the axion mass region 0.84 < m _ { a } < 1.00 eV was newly explored , where the axions in the “ photon-coupling vs. mass ” parameter region ( g _ { a \gamma } - m _ { a } ) of the preferred axion models were newly searched by this experiment .
From the absence of any evidence , a limit on axion-photon coupling constant was set to be g _ { a \gamma } < \hbox { 5.6 - -13.4 } \times 10 ^ { -10 } { GeV } ^ { -1 } at 95 % confidence level in the above mass region .