Direct search for solar axions by using strong magnetic field and X-ray detectors

We have searched for axions which could be produced in the solar core by exploiting their conversion to X rays in a strong laboratory magnetic field. The signature of the solar axion is an increase in the rate of the X rays detected in a magnetic helioscope when the sun is within its acceptance. From the absence of such a signal we set a 95% confidence level limit on the axion coupling to two photons gaγγ≡1/M<6.0×10−10 GeV−1, provided the axion mass ma<0.03 eV. The limit on the coupling is factor 4.5 more stringent than the recent experimental result. This is the first experiment whose sensitivity to gaγγ is higher than the limit constrained by the solar age consideration.