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 GW(f) = 3 (f=900Hz)3, of 3 < 0:33, assuming a value of the Hubble parameter of h100 = 0:72. These new limits are a factor of seven better than the previous best in this frequency band.