Preliminary results on the operation of a 2270 kg cryogenic gravitational-wave antenna with a resonant capacitive transducer and a dc SQUID amplifier

In November 1985 the gravitational-wave antenna of the Rome group, installed at CERN, has started operating. It consists of a 5056 aluminium cilinder 3 m long, 2270 kg heavy, cooled at 4.2 K. The antenna vibrations are detected by means of a resonant capacitive transducer that together with the bar makes a two-coupled-oscillator system. The low-noise amplification is obtained with a d.c. SQUID amplifier. The frequencies of the two resonant modes are:v -=907.116 Hz andv +=923.083 Hz, with merit factorsQ -=3.2·106 andQ +=5.6·106. The sensitivity to short gravitational bursts, expressed in terms of effective noise temperature, is 18 mK. This corresponds to a change in the metric tensor whose Fourier transform isH=1.1·10-21 Hz-1. For monochromatic waves the antenna is sensitive (SNR=1) toh~2·10-25 in a band width of about 1/3 Hz, with a three months integration time.