POLARBEAR

POLARBEAR
Josquin.errard · CC BY-SA 3.0 · source
Name	POLARBEAR
Type	Cosmic microwave background polarimeter
Location	Atacama Desert, Chile
Established	2012
Operator	POLARBEAR Collaboration

POLARBEAR

POLARBEAR is a ground-based cosmic microwave background experiment focused on measuring CMB polarization anisotropies to study inflation, gravitational lensing, and primordial gravitational waves. Deployed in the Atacama Desert high plateau, it operated alongside contemporaries to complement surveys from Planck (spacecraft), BICEP2, and the South Pole Telescope. The instrument integrates technologies developed by teams affiliated with institutions such as UC Berkeley, Princeton University, Lawrence Berkeley National Laboratory, and KEK.

Overview

The POLARBEAR project originated from collaborations among researchers at University of California, Berkeley, Stanford University, Columbia University, and NIST, with site operations coordinated with the ALMA region authorities near San Pedro de Atacama. The experiment sought small-scale polarization signals first targeted by earlier missions like WMAP and later refined by Planck (spacecraft), and worked contemporaneously with projects such as BICEP2, SPTpol, and ACTPol. POLARBEAR’s instrument platform was designed to measure E-mode and B-mode polarization over angular scales that probe both recombination-era signatures and lensing from large-scale structure traced by surveys including Sloan Digital Sky Survey, Dark Energy Survey, and CFHTLenS.

Scientific goals and instrumentation

POLARBEAR aimed to detect and characterize B-mode polarization signatures induced by primordial gravitational waves predicted by inflationary models advanced by theorists connected to institutions like Princeton University, Harvard University, and Cambridge University. Secondary goals included measuring lensing B-modes produced by intervening matter distributions studied by collaborations such as Planck (spacecraft), Herschel Space Observatory, and Euclid (spacecraft), and cross-correlating with galaxy catalogs from SDSS and WISE. The instrument employed transition-edge sensor (TES) bolometers developed with support from NIST, coupled to antenna-coupled detector arrays inspired by designs from Jet Propulsion Laboratory and Caltech. POLARBEAR used a cryogenic receiver, a rotating half-wave plate similar to approaches used by ABS (experiment) and EBEX, and a Gregorian telescope optics scheme comparable to designs deployed by SPTpol and ACTPol. Readout systems used multiplexing techniques pioneered at SLAC National Accelerator Laboratory and Argonne National Laboratory.

Observations and data processing

Observations were conducted from the Atacama Large Millimeter Array region, leveraging dry, high-altitude conditions shared with facilities like ALMA and APEX. Survey strategies included deep fields overlapping areas observed by Herschel Space Observatory and Spitzer Space Telescope to enable multiwavelength cross-correlation with catalogs from 2MASS and WISE. Data acquisition followed protocols developed in coordination with teams at Lawrence Berkeley National Laboratory, Jet Propulsion Laboratory, and Caltech, while time-domain filtering and map-making pipelines drew on algorithms used by Planck (spacecraft) and WMAP. Systematics mitigation incorporated beam characterization techniques refined in experiments such as BICEP2 and QUaD, and polarization calibration compared to polarized sources cataloged by VLA and ATCA. Data processing used high-performance computing facilities at National Energy Research Scientific Computing Center and analysis tools referencing methods from HEALPix developers and statistical approaches common in work by Max Planck Institute for Astrophysics teams.

Key results and publications

POLARBEAR produced measurements of small-scale B-mode power consistent with gravitational lensing predictions and set upper limits on inflationary tensor-to-scalar ratio r at its targeted angular scales, results that were placed in context with constraints from Planck (spacecraft), BICEP2, and Keck Array. Key publications appeared in journals frequented by researchers from Physical Review Letters, Astrophysical Journal, and Journal of Cosmology and Astroparticle Physics, with author lists including members from UC Berkeley, Princeton University, Stanford University, Columbia University, and University of Chicago. Published analyses discussed delensing prospects relevant to future missions like LiteBIRD, CMB-S4, and Simons Observatory, and compared foreground mitigation strategies with studies by WMAP and Planck (spacecraft). POLARBEAR’s data releases informed joint analyses combining maps from SPTpol and ACTPol teams, and were cited in theoretical work by groups at Perimeter Institute, Institute for Advanced Study, and CERN.

Collaboration and funding

The POLARBEAR Collaboration encompassed institutions including University of California, Berkeley, Princeton University, Stanford University, Columbia University, University of Chicago, University of Colorado Boulder, KEK, and National Astronomical Observatory of Japan. Funding agencies supporting POLARBEAR included grants from National Science Foundation (United States), Department of Energy (United States), Japan Society for the Promotion of Science, and institutional contributions from Lawrence Berkeley National Laboratory. Collaborative governance followed models used by multi-institution experiments like Planck (spacecraft), ALMA, and South Pole Telescope, coordinating observing time allocations and data access agreements among partner institutions such as NIST and SLAC National Accelerator Laboratory.

Category:Cosmic microwave background experiments