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

Abstract

The Atacama B-mode Search (ABS) is an experiment designed to measure cosmic microwave background (CMB) polarization at large angular scales ( > 40). It operated from the ACT site at 5190 m elevation in northern Chile at 145 GHz with a net sensitivity (NEQ) of 41 µK √ 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 • and right ascension 25 • . 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.The ABS instrument, shown in Fig. 1a, is a 145 GHz polarization-sensitive bolometric receiver and cryogenic telescope. Its key characteristics are presented in Table 1. It is integrated into a standard shipping container for rapid deployment. A hoist system elevates the az-el mounted cryostat onto the roof of the container from where it scans the sky. A co-moving ground screen that shields the receiver from terrestrial radiation is attached after the mount is hoisted into position. The ground screen supplements a conical baffle at the window to the cryostat.1 The array NET is calculated from the median NET of each detector that passes the data selection; the number quoted here refers to observations of Field A.2 The PWV is estimated with data from the Atacama Pathfinder EXperiment (APEX) Weather Monitor: http://www.apex-telescope.org/weather/Historical_weather/index.htm.3 All reported temperatures for the CMB and detector-related quantities are relative to the CMB.

Improved Constraints on Primordial Gravitational Waves using Planck , WMAP, and BICEP/ Keck Observations through the 2018 Observing Season

“…[50] with the purple region being natural inflation. [20,39,[51][52][53][54][55][56][57][58][59][60] and detections [61][62][63]. Theoretical predictions are shown for the lensing B modes (solid red) that peak at arcminute scales (multipole l ∼ 1000), and for gravitational wave B modes (dashed red) for two values of r peaking at degree scales ðl ∼ 80Þ.…”

Constraints on Primordial Gravitational Waves Using Planck , WMAP, and New BICEP2/ Keck Observations through the 2015 Season

“…Probing for these primordial gravitational waves through the faint B-mode polarization patterns that they would imprint on the CMB is recognized as one of the most important goals in cosmology today, with the potential to either confirm inflation, and establish its energy scale, or to powerfully limit the space of allowed inflationary models [5]. Multiple groups are making measurements of CMB polarization, some focused on the gravitational wave goal at larger angular scales, and others focused on other science at smaller angular scalesexamples include [6][7][8][9].…”

The Simons Observatory Large Aperture Telescope Receiver

“…High-resolution (~¢ 1 ) experiments, such as the Atacama Cosmology Telescope (ACT; Thornton et al 2016) and the South Pole Telescope (SPT; Carlstrom et al 2011;Sayre et al 2020) have made measurements of both the primordial temperature power spectrum (Wu et al 2019) as well as secondary anisotropies such as the thermal and kinematic Sunyaev-Zel'dovich (SZ) effects (Sunyaev & Zeldovich 1970, 1972Hilton et al 2018) and gravitational lensing effects (Story et al 2015). Lowresolution experiments (∼0°.5), such as the BICEP and Keck Arrays (Ade et al 2014a;Keck Array and BICEP2 Collaborations et al 2018), the SPIDER (Gualtieri et al 2018), the Atacama B-mode Survey (ABS; Kusaka et al 2018), the POLARBEAR (Ade et al 2014b;Polarbear Collaboration et al 2020), and the Cosmology Large Angular Scale Surveyor (CLASS; Harrington et al 2016;) aim to improve measurements on B-mode polarization, one of the two components in CMB polarization (Hu & White 1997), at larger angular scales (ℓ  200).…”