Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors

Abstract

Searches for a stochastic gravitational-wave background (SGWB) using terrestrial detectors typically involve cross-correlating data from pairs of detectors. The sensitivity of such cross-correlation analyses depends, among other things, on the separation between the two detectors: the smaller the separation, the better the sensitivity. Hence, a co-located detector pair is more sensitive to a gravitational-wave background than a nonco-located detector pair. However, co-located detectors are also expected to suffer from correlated noise from instrumental and environmental effects that could contaminate the measurement of the background. Hence, methods to identify and mitigate the effects of correlated noise are necessary to achieve the potential increase in sensitivity of co-located detectors. Here we report on the first SGWB analysis using the two LIGO Hanford detectors and address the complications arising from correlated environmental noise. We apply correlated noise identification and mitigation techniques to data taken by the two LIGO Hanford detectors, H1 and H2, during LIGO's fifth science run. At low frequencies, 40 − 460 Hz, we are unable to sufficiently mitigate the correlated noise to a level where we may confidently measure or bound the stochastic gravitational-wave signal. However, at high frequencies, 460 − 1000 Hz, these techniques are sufficient to set a 95% confidence level (C.L.) upper limit on the gravitational-wave energy density of Ω(f ) < 7.7 × 10 −4 (f /900 Hz) 3 , which improves on the previous upper limit by a factor of ∼ 180. In doing so, we demonstrate techniques that will be useful for future searches using advanced detectors, where correlated noise (e.g., from global magnetic fields) may affect even widely separated detectors.

Detection methods for stochastic gravitational-wave backgrounds: a unified treatment

“…2014):The bounds for are (Aasi et al. 2014, 2015):We note that the bound for the frequency band comes from a correlation analysis using the colocated 2 km and 4 km Hanford detectors (Aasi et al. 2015).…”

Stochastic gravitational wave backgrounds

“…In reality, the two detectors will be displaced from one another, so the detected signal will not be quite the same; the consequences of this will be articulated below. Also, having two co-located detectors typically leads to common noise, as was the case for initial LIGO when it used two co-located detectors to attempt to measure the stochastic background [55]; Advanced LIGO does not have co-located detectors. As a consequence, LIGO and Virgo are attempting to measure the stochastic background through the correlation of the output of detectors displaced thousands of kilometers from one another.…”

First search for a stochastic gravitational-wave background from ultralight bosons

“…In this work we will focus on the case of two detectors for simplicity, but the formalism can be extended to handle a larger network of detectors [42,43]. Following the notation of [67], we define a cross-correlation estimator for each frequency bin [43,68] as,Ĉ…”