Abstract
We report the experimental results of a prototype balance for the Archimedes experiment, devoted to measure the interaction between quantum vacuum energy and gravity. The prototype is a beam balance working at room temperature which shares with the final balance several mechanical and optical components. The balance sensitivity has been tested at the site of the Virgo gravitational wave detector in order to benefit from its quiet environment and control facilities. This allowed also the test of the coherence of the balance data with the Virgo interferometer signal and with the environmental data. In the low-frequency regime, the balance has shown a sensitivity of about 8times 10^{-12} {text {Nm}}/sqrt{text {Hz}}, which is among the best in the world, and it is very promising toward the final Archimedes measurement. In the high-frequency region, above a few Hz, relying on the behavior of the balance as a rotational sensor, the ground tilt has been measured in view of the next work devoted to Newtonian noise subtraction (NNS) in Virgo. The measured ground tilt reaches a minimum of about 8times 10^{-11} {text {rad}}/sqrt{{text {Hz}}} in the few Hz region and ranges from 10^{-10} to 10^{-9} {text {rad}}/sqrt{{text {Hz}}} in the 10–20 Hz region, where a very interesting coherence, at some frequencies, with the Virgo interferometer signal is shown.
Highlights
Within the framework of macroscopic detectors of small forces, Archimedes collaboration recently proposed a beam balance to measure the force exerted by the gravitational field on a rigid Casimir cavity
The force to be measured is called the Archimedes force of vacuum, as it corresponds to the weight of the vacuum fluctuation modes that are expelled by the Casimir cavity [16,17]
The second condition has been fulfilled by designing the interferometer in such a way that the angular and translation separations of the two interfering beams are of the second order with respect to the arm tilts
Summary
The final apparatus will work in a cryogenic environment that implies a long recovery time for each intervention on the balance For this reason, the readout of the prototype balance has already been designed to be robust and to have a high dynamic range, in order to pledge its capability in recovering the correct interferometer signal even in case of high deviations from the working point. The balance has been initially assembled and tested in the Naples laboratory; it has been installed at the Virgo site, which is seismically more quiet, in the North-end building In this setup, the balance has been tested for the torque sensitivity in the low-frequency regime, while at high frequencies it has been operated as a tiltmeter (rotational sensor).
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