Picoradiant tiltmeter and direct ground tilt measurements at the Sos Enattos site

Abstract We report the tilt sensitivity reached by ARCHIMEDES tiltmeter in 2–20 Hz frequency region, where seismic noise is expected to give an important limitation next future Gravitational Waves detection, particularly through Newtonian noise. The level $$\tilde{\theta }(f)$$ θ ~ ( f ) about $$10^{-12} \mathrm{rad}/\sqrt{\mathrm{Hz}}$$ 10 - 12 rad / Hz most of band, reaching minimum } = 7\cdot 10^{-13} = 7 · 13 around 9 Hz. a beam balance with 0.5 m suspended arm and interferometric optical readout, working closed loop. results have been obtained direct measurement ground at Sos Enattos site (Sardinia, Italy). This requirement use as part effective reduction system for present detectors, also confirms that among quietest sites world, suitable host third-generation detector Einstein Telescope.