Improved Measurements of the CMB Power Spectrum with ACBAR

We report improved measurements of temperature anisotropies in the cosmicmicrowave background (CMB) radiation made with the Arcminute CosmologyBolometer Array Receiver (ACBAR). In this paper, we use a new analysistechnique and include 30% more data from the 2001 and 2002 observing seasonsthan the first release to derive a new set of band-power measurements withsignificantly smaller uncertainties. The planet-based calibration usedpreviously has been replaced by comparing the flux of RCW38 as measured byACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR.The resulting power spectrum is consistent with the theoretical predictions fora spatially flat, dark energy dominated LCDM cosmology including the effects ofgravitational lensing. Despite the exponential damping on small angular scales,the primary CMB fluctuations are detected with a signal-to-noise ratio ofgreater than 4 up to multipoles of l=2000. This increase in the precision ofthe fine-scale CMB power spectrum leads to only a modest decrease in theuncertainties on the parameters of the standard cosmological model. At highangular resolution, secondary anisotropies are predicted to be a significantcontribution to the measured anisotropy. A joint analysis of the ACBAR resultsat 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000shows that the power, reported by CBI in excess of the predicted primaryanisotropy, has a frequency spectrum consistent with the thermalSunyaev-Zel'dovich effect and inconsistent with primary CMB. The resultsreported here are derived from a subset of the total ACBAR data set; the finalACBAR power spectrum at 150 GHz will include 3.7 times more effectiveintegration time and 6.5 times more sky coverage than is used here.Comment: 19 pages, 9 figures, Ap