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Enabling Co-Located Interferometric Detectors for Upper Limits on Stochastic Gravitational Waves

This presentation discusses advancements in co-located interferometric detectors, focusing on the H1-H2 configuration to achieve upper limits on the stochastic gravitational wave background. Notable improvements in sensitivity, especially at higher frequencies, are reported despite environmental correlations. Techniques like the coherence squared function and vetoing environmental influences are detailed, leading to valuable insights into instrument noise. The impact of enhanced detector capabilities on astrophysical source detection and future publication of results are also explored, advancing the field of gravitational wave research.

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Enabling Co-Located Interferometric Detectors for Upper Limits on Stochastic Gravitational Waves

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  1. Toward Enabling Co-Located Interferometric Detectors to Provide Upper Limits on the Stochastic Gravitational Wave Background Nick Fotopoulos, MIT On Behalf of the LIGO Scientific Collaboration 2005-12-15 GWDAW-10 @ UT Brownsville

  2. Co-Located Interferometers: Overlap Reduction Function H1-H2 promises significantly enhanced sensitivity over H1-L1, especially at higher frequencies BUT Co-located detectors are subject to environmental correlation

  3. H1-H2 Coherence (S4) Coherence squared f (Hz) Very coherent in the instrument’s “sweet spot”. N = 109821 1/N ≈ 9.1·10-6 S1-S4 measurements of eff not consistent with zero

  4. S1 Results S1

  5. Squaring Coherence Sensitivity Theorem: For all Z{PEM channels}, coh(H1,H2)≥coh(H1,Z)•coh(H2,Z) Corollary: coh(H1,H2)≥ coh(H1,Z)•coh(H2,Z) max Z 1/N 1/N 1/N2

  6. Tracking Environmental Coupling in H1-H2 S4 had 107PEM channels in RDS_R_L1 S5 will have roughly the same

  7. Maximum of PEM Coherence Products: Frequency Veto Vetoed regions (H1-H2 1/N ~ 10-5, PEM-IFO 1/N ~10-4 due to resolution choices) Threshold10-5.5 1/N2 • Maximum of PEM coherence products follows H1-H2 measured • coherence very closely (within error) • With this (semi-arbitrary) threshold, 56% bins lost in [50,350]Hz • and 48% bins lost in [50,500]Hz, 30% in [50,1024]Hz

  8. coh(H1,H2) post-vetohistogram  exp(-N2) Success! • This (unreviewed) pipeline results in noticeably reduced • significance for the point estimate • We have physical basis for veto We are one step closer to setting upper limits with the H1-H2 pair!

  9. Detector Characterization Have determined environmental coupling out to 1kHz. Can identify strongest sources at each frequency!

  10. A Few Words on instr eff = instr+ GW • We must estimate or bound instr • Attempts to take this into account in S3 resulted in an GW upper limit a few times worse than the H1-L1 upper limit • As we have flagged and eliminated the major sources of instrumental correlation, instr is greatly reduced • Other sources: Incomplete PEM coverage, non-linear environmental couplings…

  11. H1-H2 and the Future • The new technique: Take maximum across coherence products coh(H1,Z)*coh(H2,Z). • The new capability: H1-H2 can provide upper limits at high frequencies, which are inaccessible to H1-L1. • S4 was playground and proof of concept; will not publish upper limit from H1-H2. • S5 will have “blind” frequency vetoes and the resulting point estimate is planned for publication. • With some confidence in H1-H2, we can begin looking for astrophysical sources of stochastic radiation, which is expected to peak at frequencies >200Hz.

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