Results from the Atacama B-mode Search (ABS) Experiment

TL;DR

The ABS experiment measured large-scale CMB polarization, finding consistency with Planck data, marginal dust detection, and setting an upper limit on tensor-to-scalar ratio, while introducing new HWP-based analysis methods.

Contribution

This paper presents new measurements of CMB polarization at large scales, including a novel analysis approach using a rotating sapphire half-wave plate.

Findings

Agreement with Planck TE and EE measurements

Marginal detection of polarized dust emission

Upper limit on tensor-to-scalar ratio of r<2.3

Abstract

The Atacama B-mode Search (ABS) is an experiment designed to measure cosmic microwave background (CMB) polarization at large angular scales ($\ell>40$). It operated from the ACT site at 5190~m elevation in northern Chile at 145 GHz with a net sensitivity (NEQ) of 41 $\mu$K$\sqrt{\rm s}$. It employed an ambient-temperature sapphire half-wave plate rotating at 2.55 Hz to modulate the incident polarization signal and reduce systematic effects. We report here on the analysis of data from a 2400 deg$^2$ patch of sky centered at declination $-42^\circ$ and right ascension $25^\circ$. We perform a blind analysis. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky. We marginally detect polarized dust emission and give an upper limit on the tensor-to-scalar ratio of $r<2.3$ (95% cl) with the equivalent of 100 on-sky days of observation. We also present a new measurement of the polarization of Tau A and introduce new methods associated with HWP-based observations.