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 magnet ic 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% confid ence level limit on the axion coupling to two photons g(a gamma gamma) 1/M < 6.0 x 10(-10) GeV-1, provided the axion mass m(a) < 0.03 eV. Th e limit on the coupling is factor 4.5 more stringent than the recent e xperimental result. This is the first experiment whose sensitivity to g(a gamma gamma) is higher than the limit constrained by the solar age consideration. (C) 1998 Elsevier Science B.V. All rights reserved.