Detection of cosmic microwave background structure in a second field with the Cosmic Anisotropy Telescope

We describe observations at frequencies near 15 GHz of the second 2 x 2 deg(2) field imaged with the Cambridge Cosmic Anisotropy Telescope (CAT), After the removal of discrete radio sources, structure is detected in the images on characteristic scales of about half a degree, corresponding to spherical harmonic multipoles in the range l approximate to 330-680, A Bayesian analysis confirms that the signal arises predominantly from the cosmic microwave background (CMB) radiation for multipoles in the lower half of this range; the average broad-band power in a bin with centroid l = 422 (theta approximate to 51 arcmin) is estimated to be Delta T/T = 2.1(-0.5)(+0.4) X 10(-5). For multipoles centred on l = 615 (theta approximate to 35 arcmin), we find contamination from Galactic emission is:significant, and constrain the CMB contribution to the measured power in this bin to be Delta T/T < 2.0 x 10(-5) (1 sigma upper limit). These new results are consistent with the first detection made by CAT in a completely different area of sky. Together with data from other experiments, this new CAT detection adds weight to earlier evidence from CAT for a downturn in the CMB power spectrum on scales smaller than 1 deg. improved limits on the values of H-0 and Omega are determined using the new CAT data.