A MEASUREMENT OF THE DAMPING TAIL OF THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM WITH THE SOUTH POLE TELESCOPE

We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) using data from the South Pole Telescope (SPT). The data consist of 790 square degrees of sky observed at 150 GHz during 2008 and 2009. Here we present the power spectrum over the multipole range 650 < ‘ < 3000, where it is dominated by primary CMB anisotropy. We combine this power spectrum with the power spectra from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data release to constrain cosmological models. We nd that the SPT and WMAP data are consistent with each other and, when combined, are well t by a spatially at, CDM cosmological model. The SPT+WMAP constraint on the spectral index of scalar uctuations is ns = 0:9663 0:0112. We detect, at 5 signicance, the eect of gravitational lensing on the CMB power spectrum, and nd its amplitude to be consistent with the CDM cosmological model. We explore a number of extensions beyond the CDM model. Each extension is tested independently, although there are degeneracies between some of the extension parameters. We constrain the tensorto-scalar ratio to be r < 0:21 (95% CL) and constrain the running of the scalar spectral index to be dns=d lnk = 0:024 0:013. We strongly detect the eects of primordial helium and neutrinos on the CMB; a model without helium is rejected at 7.7 , while a model without neutrinos is rejected at 7.5 . The primordial helium abundance is measured to be Yp = 0:296 0:030, and the eective number of relativistic species is measured to be Ne = 3:85 0:62. The constraints on these models are strengthened when the CMB data are combined with measurements of the Hubble constant and the baryon acoustic oscillation feature. Notable improvements include ns = 0:9668 0:0093, r < 0:17 (95% CL), and Ne = 3:86 0:42. The SPT+WMAP data show a mild preference for low power in the CMB damping tail, and while this preference may be accommodated by models that have a negative spectral running, a high primordial helium abundance, or a high eective number of relativistic species, such models are disfavored by the abundance of low-redshift galaxy clusters. Subject headings: cosmology { cosmology:cosmic microwave background { cosmology: observations { large-scale structure of universe