Measurements of B-mode Polarization of the Cosmic Microwave Background from 500 Square Degrees of SPTpol Data

Abstract

We report a B-mode power spectrum measurement from the cosmic microwave background (CMB) polarization anisotropy observations made using the SPTpol instrument on the South Pole Telescope. This work uses 500 deg\(^2\) of SPTpol data, a five-fold increase over the last SPTpol B-mode release. As a result, the bandpower uncertainties have been reduced by more than a factor of two, and the measurement extends to lower multipoles: \(52 < \ell < 2301\). Data from both 95 and 150 GHz are used, allowing for three cross-spectra: 95 GHz x 95 GHz, 95 GHz x 150 GHz, and 150 GHz x 150 GHz. B-mode power is detected at very high significance; we find \(P(BB < 0) = 5.8 \times 10^{-71}\), corresponding to a \(18.1 \sigma\) detection of power. An upper limit is set on the tensor-to-scalar ratio, \(r < 0.44\) at 95% confidence (the expected \(1 \sigma\) constraint on \(r\) given the measurement uncertainties is 0.22). We find the measured B-mode power is consistent with the Planck best-fit \(\Lambda\)CDM model predictions. Scaling the predicted lensing B-mode power in this model by a factor Alens, the data prefer Alens = \(1.17 \pm 0.13\). These data are currently the most precise measurements of B-mode power at \(\ell > 320\).