The ALTAIR cryogenic gravitational-wave experiment

Summary We report on the experimental results obtained with the cryogenic Gravitational-Wave resonant detector ALTAIR located in Frascati (Italy) at the Istituto di Fisica dello Spazio Interplanetario of Consiglio Nazionale delle Ricerche. The peculiarity of this experiment is its working frequency. The first longitudinal mode of resonance of the antenna is at 1.8 kHz. The antenna, now equipped with a resonant capacitive transducer and a d.c. SQUID preamplifier, after a first test in November 1989, has operated almost continuously from May 1990. The best sensitivity, recently reached, expressed in terms of the effective noise temperatureT _eff, is 20 mK, corresponding, for a short pulse of gravitational wave, to a metric perturbationh of 3×10⁻¹⁸. In the last period of measurements (from April 1991 to March 1992) two other antennas were operating: the Explorer antenna (2300 kg,T=2.0 K) at CERN in Geneva and the LSU antenna (2500 kg,T=4.2 K) at Louisiana State University in USA, both having a resonant frequency below 1 kHz. The data of these three detectors can be remote observed, in real time, by the international computer network. Coincidence analysis between the data of these three detectors is in progress. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990 (updated version).