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 < ell <
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 find
that the SPT and WMAP data are consistent with each other and, when combined,
are well fit by a spatially flat, LCDM cosmological model. The SPT+WMAP
constraint on the spectral index of scalar fluctuations is ns = 0.9663 +/-
0.0112. We detect, at ~5-sigma significance, the effect of gravitational
lensing on the CMB power spectrum, and find its amplitude to be consistent with
the LCDM cosmological model. We explore a number of extensions beyond the LCDM
model. Each extension is tested independently, although there are degeneracies
between some of the extension parameters. We constrain the tensor-to-scalar
ratio to be r < 0.21 (95% CL) and constrain the running of the scalar spectral
index to be dns/dlnk = -0.024 +/- 0.013. We strongly detect the effects of
primordial helium and neutrinos on the CMB; a model without helium is rejected
at 7.7-sigma, while a model without neutrinos is rejected at 7.5-sigma. The
primordial helium abundance is measured to be Yp = 0.296 +/- 0.030, and the
effective number of relativistic species is measured to be Neff = 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 Neff = 3.86 +/- 0.42. The SPT+WMAP data show...
