Improved Measurements of the CMB Power Spectrum with ACBAR

We report improved measurements of temperature anisotropies in the cosmic background (CMB) radiation made with the Arcminute Cosmology Array Receiver (ACBAR). In this paper, we use a new analysis and include 30% more data from the 2001 and 2002 observing seasons the first release to derive a new set of band-power measurements with smaller uncertainties. The planet-based calibration used has been replaced by comparing the flux of RCW38 as measured by and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR. resulting power spectrum is consistent with the theoretical predictions for spatially flat, dark energy dominated LCDM cosmology including the effects of lensing. Despite the exponential damping on small angular scales, primary CMB fluctuations are detected with a signal-to-noise ratio of than 4 up to multipoles of l=2000. This increase in the precision of fine-scale CMB power spectrum leads to only a modest decrease in the on the parameters of the standard cosmological model. At high resolution, secondary anisotropies are predicted to be a significant to the measured anisotropy. A joint analysis of the ACBAR results 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000 that the power, reported by CBI in excess of the predicted primary, has a frequency spectrum consistent with the thermal-Zel'dovich effect and inconsistent with primary CMB. The results here are derived from a subset of the total ACBAR data set; the final power spectrum at 150 GHz will include 3. 7 times more effective time and 6. 5 times more sky coverage than is used here.