Impact of correlated seismic and correlated Newtonian noise on the Einstein Telescope

TL;DR

This study investigates how correlated seismic and Newtonian noise could hinder the detection of the gravitational wave background at the Einstein Telescope, especially from body waves, and explores mitigation strategies.

Contribution

It provides the first detailed analysis of correlated seismic and Newtonian noise impacts on the Einstein Telescope's sensitivity and proposes limits for seismic coupling to mitigate these effects.

Findings

Correlated seismic noise from Rayleigh waves affects the detector up to ~5 Hz.

Newtonian noise from body waves could be 5-7 orders of magnitude above sensitivity below 40 Hz.

NN cancellation could reduce noise effects above 30 Hz.

Abstract

Correlated noise could impact the search for the gravitational wave background at future Earth-based gravitational-wave detectors. Due to the small distance ($\sim$ 400 m) between the different interferometers of the Einstein Telescope, correlated seismic noise could have a significant effect. To this extent, we study the seismic correlations at the Earth's surface, as well as underground, between seismometers and geophones separated by several hundreds of meters, in the frequency range 0.05 Hz - 50 Hz. Based on these correlated seismic fields we predict the levels of correlated Newtonian noise (NN). We construct upper limits on the allowed seismic coupling function such that correlated seismic noise does not affect the search for an isotropic gravitational wave background. Assuming a facility located 300 m below the surface, the impact on the search for a gravitational wave background of correlated NN from Rayleigh waves are found to be problematic up to $\sim$ 5 Hz. The NN from body waves, however, constitutes a serious threat to the search of a gravitational wave background. Correlated NN from body waves could be up to five to seven orders of magnitude above the planned sensitivity at $\sim$ 3 Hz and it could impede any search for a gravitational wave background below 40 Hz. With a factor 10 of NN reduction via NN cancellation in each interferometer, the effects of the NN on the stochastic search could be eliminated above 30 Hz.