The cosmic microwave background power spectrum out to  = 1400 measured by the Very Small Array

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2° at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles ℓ = 160 and 1400. Such measurements at high ℓ are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall-off in power at high ℓ and starts to constrain the position and height of a fourth peak.