1. Newtonian Noise Mitigation with Tensor Gravitational Wave Detector
Ho Jung Paik Department of Physics, University of Maryland 8th Japan-Korea Joint Workshop June 27, 2015

2. Superconducting tensor gravitational wave detector
(Superconducting Omni-directional Gravitational Radiation Observatory)
SOGRO
Rayleigh NN must be mitigated by 102 at 0.1 Hz for SOGRO 1
Infrasound NN must be mitigated by 103 at 0.1 Hz for SOGRO 1.
Paik

3. Newtonian gravity noise
Seismic and atmospheric density modulations cause Newtonian gravity gradient noise.
At 0.1 Hz, s ~ 35 km >> L.
 Gravity gradient noise  L.
 Detecting and removing the gravity gradient noise appears to be very challenging.
GWs are transverse and cannot have longitudinal components whereas the Newtonian gradient does.
 GW could be distinguished from near-field gradients, if all the tensor components are detected.
Paik

4. NN due to Rayleigh waves
Metric perturbation tensor in the source frame:
Paik

5. Removal of Rayleigh NN az() is measured by the vertical CM channel.
With tensor (SNR 103)
+ vertical CM (SNR 106)
+ 7 seism (5 km, SNR 103)
With tensor
+ vertical CM (0 noise)
Paik

6. Removal of infrasound NN
Infrasound waves come from half space with an additional unknown: polar angle of incidence  .
Microphones are required to measure the air density fluctuations.
With tensor + 15 mikes (0, 0.6, 1 km, SNR 104)
Harms and Paik, PRD (2015)
Satisfies SOGRO 1 requirement
Is there any way that we can mitigate NN by using the tensor channels alone?
Paik

7. NN mitigation by correlation?
Rayleigh and infrasound waves incident in different angles are uncorrelated with each other and with the GW signal.
This allows us to determine autocorrelations of h+() and h() by combining correlations of various tensor outputs.
Fourier transform of autocorrelation is power spectral density.
Problem: It takes a long time to mitigate the NN by using correlation method.
Paik

8. Could SOGRO help advanced detectors mitigate NN? (HW from R. Weiss)
Newtonian noise
Worthy mitigation goal
Worthy mitigation goal:
A factor of ~10 to Hz-1/2 at 10 Hz and Hz-1/2 at 1 Hz.
Paik

9. KAGRA sensitivity curve
The low-frequency noise of KAGRA could benefit from a similar NN rejection.
Paik

10. Sensitivities to GW and NN
At 1-10 Hz, cR = 250 m/s (surface), 3.5 km/s (deep underground).
 NN is uncorrelated between detector test masses.
Paik

11. Incomplete correlation of NN
Mitigation factor S is given by the correlation CSN between the detector and the NN sensor:
Beker et al., GRG 43, 623 (2011)
It is much more challenging to mitigate the NN of ground detectors.
Paik

12. Mini-SOGRO with 5-m arm length
L = 5 m, M = 1 t, T = 0.1 K, Q = 109, n = 2, fD = 1 Hz
Mini-SOGRO with L = 5 m, M = 1 ton, T = 0.1 K could mitigate the NN at 1-10 Hz by a factor  5.
 NN mitigation appears very challenging but not impossible.
Paik