Observation of a potential future sensitivity limitation from ground motion at LIGO Hanford

Abstract

A first detection of terrestrial gravity noise in gravitational-wave detectors is a formidable challenge.With the help of environmental sensors, it can in principle be achieved before the noise becomes dominantby estimating correlations between environmental sensors and the detector. The main complication is todisentangle different coupling mechanisms between the environment and the detector. In this paper, weanalyze the relations between physical couplings and correlations that involve ground motion and LIGOstrain data h(t) recorded during its second science run in 2016 and 2017. We find that all noise correlatedwith ground motion was more than an order of magnitude lower than dominant low-frequency instrumentnoise, and the dominant coupling over part of the spectrum between ground and h(t) was residual couplingthrough the seismic-isolation system. We also present the most accurate gravitational coupling model so farbased on a detailed analysis of data from a seismic array. Despite our best efforts, we were not able tounambiguously identify gravitational coupling in the data, but our improved models confirm previouspredictions that gravitational coupling might already dominate linear ground-to-h(t) coupling over parts ofthe low-frequency, gravitational-wave observation band.