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

TL;DR

This paper presents a highly significant detection of B-mode polarization in the CMB using extensive SPTpol data, providing new constraints on cosmological parameters and confirming consistency with the Planck ΛCDM model.

Contribution

It reports the most precise measurements of B-mode polarization at high multipoles, extending previous results with a five-fold increase in data and improved uncertainties.

Findings

High-significance detection of B-mode power ($18.1 \sigma$)

Upper limit on tensor-to-scalar ratio $r < 0.44$

Data favor lensing amplitude Alens = $1.17 \\pm 0.13$

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 $\ell > 320$.