Detection of B-mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope

TL;DR

This paper reports the first detection of gravitational lensing B modes in the cosmic microwave background using data from the South Pole Telescope, confirming theoretical predictions and providing a new cosmological observable.

Contribution

First measurement of gravitational lensing B modes in the CMB using SPTpol data, combining polarization measurements with lensing potential estimates from Herschel-SPIRE.

Findings

Detected lensing B modes with 7.7 sigma significance

Measured correlation amplitude consistent with theoretical models

Robust detection across different analysis choices

Abstract

Gravitational lensing of the cosmic microwave background generates a curl pattern in the observed polarization. This "B-mode" signal provides a measure of the projected mass distribution over the entire observable Universe and also acts as a contaminant for the measurement of primordial gravity-wave signals. In this Letter we present the first detection of gravitational lensing B modes, using first-season data from the polarization-sensitive receiver on the South Pole Telescope (SPTpol). We construct a template for the lensing B-mode signal by combining E-mode polarization measured by SPTpol with estimates of the lensing potential from a Herschel-SPIRE map of the cosmic infrared background. We compare this template to the B modes measured directly by SPTpol, finding a non-zero correlation at 7.7 sigma significance. The correlation has an amplitude and scale-dependence consistent with theoretical expectations, is robust with respect to analysis choices, and constitutes the first measurement of a powerful cosmological observable.