Newtonian Noise J A N H A R M S & V U K M A N D I C J O I N T E T / C E S Y M P O S I U M F L O R E N C E,

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1 Newtonian Noise 1 J A N H A R M S & V U K M A N D I C J O I N T E T / C E S Y M P O S I U M F L O R E N C E,

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3 Modelling Seismic NN 3 Density fluctuation inside medium Surface displacement Seismic NN Seismic spectra vary between sites Each shear wave drives surface and cavity wall displacement coherently Each compressional wave drives density changes, and surface as well as cavity wall displacement coherently

4 Seismic Scattering 4 Rf R R M P SV P P S P Plane-wave P S conversion happens at reflection from flat surfaces. Rf waves can also be produced by underground sources, but this requires non-plane wave fronts. Wave conversion happens between all wave types. Scattering matrix is determined by surface topography.

5 Seismic NN 5 Seismic NN in a surface detector Seismic NN in an underground detector Seismic models: Body wave: 3x 12x LNM, Surface: 50x 1000x LNM Rayleigh dispersion model: 1Hz 10Hz Includes contributions from cavity-wall displacement Homogeneous half space (except for Rayleigh dispersion)

6 Global Seismic Records 6 Central Australia (e.g. Warramunga seismic array): 2x LNM in meter-deep vaults above 2Hz Near Ojos del Salado in Andes of Chile and Argentina: 2x LNM above 2Hz Bogoin borehole station in Central African Republic: almost equal to LNM above 1.3Hz Antarctica deep vault, e.g. at Siple Dome: below LNM between 1.3 4Hz

7 Modelling Atmospheric NN 7 Atmospheric NN (So far poorly modelled) quasi-static temperature perturbations advected along (so far poorly modeled) streamlines Sound propagation inside atmosphere and laboratory buildings (scattering not yet simulated)

8 Atmospheric NN 8 Temperature NN Uniform air flow, v=20m/s Infrasound NN Atmospheric NN limits sensitivity of ET-type detectors if built at the surface Going underground very efficiently suppresses atmospheric NN Atmospheric NN will be extremely challenging to cancel

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10 NN Mitigation and R&D 10 Hydrodynamical simulations for atmospheric NN Homestake: composition of seismic field (body-waves, Rayleigh waves), seismic correlations NN cancellation for underground sites: we need an idea of the degree of anisotropy and inhomogeneity of bodywave fields Present: Seismometer development Near future: Alternative sensors (seismic strainmeters, tiltmeters, dilatometers) Distant future: Atmospheric tomography (LIDAR, )

11 Importance of Array Optimization 11 Rayleigh waves, c R =250m/s Body waves (1/3 P, 2/3 S), c P =5km/s Optimization can make a big difference in performance Shear waves are a huge challenge for underground NN cancellation (effectively leading to correlated seismometer noise) We haven t tried optimization of underground arrays yet We need to consider alternative sensors (tiltmeters, strainmeters, dilatometers)

12 The game of gradients Alternative Sensors 12 One tiltmeter can substitute an array of seismometers for Rayleigh NN cancellation in large-scale detectors, but it would not work in gravity gradiometers One seismic strainmeter cannot substitute an underground array of seismometers for P-wave NN cancellation in largescale detectors, but it would work for gravity gradiometers An underground array of strainmeters insignificant advantage over a seismometer array for NN cancellation in large-scale detectors Generally, combining different types of sensors can potentially be helpful for underground NN cancellation

13 Timeline for R&D 13 Numerical simulations of atmospheric perturbations Analytical/numerical work on underground NN cancellation Site characterization Sensor development Results from a first detailed site study 6/30/2017 Array optimization based on seismic correlation measurements 6/30/2017 Infrasound NN model 12/31/2017 Comparison between sites 12/31/2018 Array design including alternative sensors 12/31/2018 Temperature NN model 12/31/2019 Seismometers and possibly strain meters suitable for NN cancellation 12/31/

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15 Surface Constrains on Observatory Designs Wind noise Few meters underground or aerodynamically shaped buildings? Strong seismic noise from local sources Improve design of laboratory infrastructure? How much digging required for 40km arms? Stick ends into mountains Strong mitigation of atmospheric NN Detrimental effects on seismic NN cancellation (necessarily complex topography) Underground Detector infrastructure How to avoid elevated underground seismic noise? 15

16 Topographic Scattering Sweetwater array (TX) Coherence at 0.2Hz 16 Montana, DL=1400m Class. Quantum Grav. 29 (2012) So far, calculations of topographic scattering only carried out in Born approximation Measurements with Sweetwater array confirm that seismic correlations are complicated in regions with rough topography

17 Topography Data 17 h L 2 /(8R)=2m SRTM data can be used to carry out systematic searches, or to characterize specific sites (elevation change along arm, topographic seismic scattering, search sites for stick into mountains configuration) For elevation changes along arms, reference ellipsoid WGS84 and EGM96 geoid separation values need to be taken into account as well (when using SRTM data)

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