Newtonian gravitational noise from seismic fields will become a limiting noise source at low frequency for second-generation, gravitational-wave detectors. It is planned to use seismic sensors surrounding the detectors' test masses to coherently subtract Newtonian noise using Wiener filters derived from the correlations between the sensors and detector data. In this Letter, we use data from a seismometer array deployed at the corner station of the Laser Interferometer Gravitational Wave Observatory (LIGO) Hanford detector combined with a tiltmeter for a detailed characterization of the seismic field and to predict achievable Newtonian-noise subtraction levels. As was shown previously, cancellation of the tiltmeter signal using seismometer data serves as the best available proxy of Newtonian-noise cancellation. According to our results, a relatively small number of seismometers is likely sufficient to perform the noise cancellation due to an almost ideal two-point spatial correlation of seismic surface displacement at the corner station, or alternatively, a tiltmeter deployed under each of the two test masses of the corner station at Hanford will be able to efficiently cancel Newtonian noise. Furthermore, we show that the ground tilt to differential arm-length coupling observed during LIGO's second science run is consistent with gravitational coupling.
Bibliographical noteFunding Information:
M. C. was supported by the David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. N. M. acknowledges the Council of Scientific and Industrial Research (CSIR), India for providing financial support as Senior Research Fellow. B. S. was supported by ARC Future Fellowship FT130100329 and D. M. and B. S. are supported by the ARC Centre of Excellence for Gravitational Wave Discovery. Thanks to the Seismic Working Group of the LIGO Scientific Collaboration for the suspension model. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation and operates under cooperative Agreement No. PHY-0757058. The authors thank the LIGO Scientific Collaboration for access to the data and gratefully acknowledge the support of the U.S. National Science Foundation (NSF) for the construction and operation of the LIGO Laboratory and Advanced LIGO, as well as the Science and Technology Facilities Council (STFC) of the United Kingdom and the Max-Planck-Society (MPS) for support of the construction of Advanced LIGO. Additional support for Advanced LIGO was provided by the Australian Research Council. This Letter has been assigned LIGO document number LIGO-P1800049.
© 2018 American Physical Society.