Study of invisible axions in the galaxy

The recent astronomical and astrophysical studies strongly support the existence of non-luminous mass in the universe. As to the constituents of the non-luminous mass, two concepts are opposing: the hot and cold darkmatter. Axions are one of the candidates of the cold dark matter. The present report outlines predicted properties of the galactic axions and the present status of the detection program at KEK. In the program, a cylindrical cavity with 15.0 cm inner diameter is made, which was selected to make full use of the existing 5.2T superconducting solenoid. The TM010 mode of the cavity is tunable from 1,53GHz to 1.14GHz using a 2.0 cm diameter sapphire rod. However, there are several stop bands due to unidentifiable parastic modes. The Q-value of the empty cavity at room temperature is 97.6% of the theoretical value. Though it does not look easy to improve the sensitivity by the order of two, the authors persist in the superheterodyne method for rf signal detection. Two FET amplifiers are made to obtain a noise temperature below 10degK with a gain more than 30dB in the region 1.2-1.7GHz. After the amplification of about 60dB at cryogenic temperature, the signal is modulated to 30MHz by an image rejection mixer and amplified another 60dB. Then the IF is converted to 30kHz. By 64 channel filters, the output signal are spectrum-analyzed, sampled by CAMAC modules and stored in optical disks. The data are processed off-line after an appropriate data storage. (N.K.)