Experimental sensitivity at 1763 HZ of the Frascati cryogenic gravitational wave antenna

The experimental results obtained with a 389 kg cryogenic antenna equipped with a resonant capacitive transducer, coupled to a dc SQUID via a resonant circuit are reported. This apparatus operated in an unusual configuration with each of the three system oscillators only loosely tuned to the others. Indeed, the transducer was accidentally detuned of 160 Hz while the electrical resonance of the SQUID coupling circuit was within 120 Hz from the antenna mode. A detailed analysis shows that this setup gives an overall system sensitivity comparable to that reachable with antenna and transducer closely tuned. The best measured sensitivity to short gravitational bursts, expressed in terms of a detection noise temperature, was 70 mK, corresponding to a perturbation of the metric tensor with a given Fourier component.