Upper limits on a stochastic gravitational-wave background using LIGO   and Virgo interferometers at 600-1000 Hz
  A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of $\Omega_{\rm GW}(f) = \Omega_3 (f/900 \mathrm{Hz})^3$, of $\Omega_3 < 0.33$, assuming a value of the Hubble parameter of $h_{100}=0.72$. These new limits are a factor of seven better than the previous best in this frequency band. 
J. Abadie, B. P. Abbott, R. Abbott, T. D. Abbott, M. Abernathy, T.   Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt...
gr-qc