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

Akito Kusaka, John Appel, Thomas Essinger-Hileman, James A. Beall, Luis E. Campusano, Hsiao Mei Cho, Steve K. Choi, Kevin Crowley, Joseph W. Fowler, Patricio Gallardo, Matthew Hasselfield, Gene Hilton, Shuay Pwu P. Ho, Kent Irwin, Norman Jarosik, Michael D. Niemack, Glen W. Nixon, Michael Snolta, Lyman A. Page, Gonzalo A. PalmaLucas Parker, Srinivasan Raghunathan, Carl D. Reintsema, Jonathan Sievers, Sara M. Simon, Suzanne T. Staggs, Katerina Visnjic, Ki Won Yoon

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29 Scopus citations


The Atacama B-mode Search is an experiment designed to measure the cosmic microwave background polarization at large angular scales (0ℓ>4). It observes at 145 GHz from a site at 5,190 m elevation in northern Chile. The noise equivalent polarization temperature, or NEQ, is 41 μKs. One of the unique features of ABS is its use of a rapidly rotating ambient-temperature half-wave plate (HWP) {as the first optical element}. {The HWP spins} at 2.55 Hz to modulate the incident polarized signal at frequencies above where instrument white noise dominates over atmospheric fluctuations and other sources of low-frequency noise. We report here on the analysis of data from a 2,400 deg2 region of sky. We perform a blind analysis to reduce potential bias. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky, {with a derived calibration factor of 00.89 ± 0.1}. We marginally detect polarized dust emission {(at 3.2 σ for EE and 2.2 σ for BB)} and give an upper limit on the tensor-to-scalar ratio of r<2.3 (95% confidence level) 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 for calibration and data analysis associated with HWP-based observations.

Original languageEnglish (US)
Article number005
JournalJournal of Cosmology and Astroparticle Physics
Issue number9
StatePublished - Sep 4 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics


  • CMBR experiments
  • CMBR polarization
  • gravitational waves and CMBR polarization
  • physics of the early universe


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