[in2p3-01077230] Searching for stochastic gravitational waves using data from the two co-located LIGO Hanford detectors

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 non-co-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 CL upper limit on the gravitational-wave energy density of \Omegaf77 x 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 eg from global magnetic fields may affect even widely separated detectors



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