BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array

TL;DR

This paper reports the detection of B-mode polarization in the CMB at degree scales using the Keck Array, confirming previous findings with improved sensitivity and consistency checks, advancing our understanding of early universe physics.

Contribution

The study presents new measurements of B-mode polarization at 150 GHz with the Keck Array, confirming previous BICEP2 results and improving the detection significance.

Findings

Detection of B-mode power > 5σ over 30 < ℓ < 150

Final combined maps with 57 nK deg depth

B-mode detection significance > 6σ

Abstract

The Keck Array is a system of cosmic microwave background (CMB) polarimeters, each similar to the BICEP2 experiment. In this paper we report results from the 2012 and 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as BICEP2. We again find an excess of B-mode power over the lensed-$\Lambda$CDM expectation of $> 5 \sigma$ in the range $30 < \ell < 150$ and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with BICEP2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 $\mu$K arcmin) over an effective area of 400 deg$^2$ for an equivalent survey weight of 250,000 $\mu$K$^{-2}$. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of $> 6\sigma$.