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| POLARBEAR-2 | |
|---|---|
| Name | POLARBEAR-2 |
| Country | Japan |
| Institution | University of Tokyo |
| Collaboration | Simons Array |
| Established | 2017 |
| Telescope type | Millimeter-wave polarimeter |
POLARBEAR-2
The POLARBEAR-2 project is a ground-based millimeter-wave polarimeter designed to measure the polarization of the cosmic microwave background with high sensitivity. Conceived within the context of modern observational cosmology, the instrument builds on technologies developed for the BICEP/Keck Array, ACT, and SPT programs and operates at a site shared with experiments such as the Simons Array and ALMA. Its deployment involved international teams from institutions including the University of Tokyo, KEK, University of California, and the Simons Foundation.
POLARBEAR-2 was conceived to probe polarization signatures predicted by inflationary scenarios and structure-formation models tested by missions like Planck, WMAP, and COBE. The instrument follows a lineage that includes the original POLARBEAR experiment and contemporaneous facilities such as the Atacama Cosmology Telescope, South Pole Telescope, and the BICEP series. Major scientific questions addressed connect to probes made by collaborations like Simons Observatory and projects allied with agencies such as JAXA, NASA, and national funding bodies like the Japan Society for the Promotion of Science.
POLARBEAR-2 employs a large-aperture refracting telescope coupled to arrays of transition-edge sensor bolometers manufactured with techniques used by groups affiliated with NIST, Lawrence Berkeley National Laboratory, and KEK. The optical chain integrates anti-reflection coated lenses analogous to designs from ALMA receivers and cryogenic systems similar to those in instruments supported by ESRF and CERN collaborations. Readout uses superconducting quantum interference devices and multiplexing schemes pioneered in projects at Stanford University and Princeton University laboratories. Frequency bands were chosen to complement measurements from Planck and WMAP and to mitigate contamination studied by teams from Caltech and MIT.
The experiment operates from the Atacama Plateau near ALMA and Paranal Observatory in northern Chile, a site shared with observatories such as APEX, ACT, and optical telescopes like Very Large Telescope. Observing strategies leverage techniques developed by the Keck Array and BICEP2 teams, including deep-field integration and scan patterns coordinated with sky surveys from SDSS and DES. Site selection considered atmospheric conditions characterized by measurements from NOAA and local research stations affiliated with the Universidad de Chile and international consortia.
Primary goals include constraining primordial B-mode polarization predicted by inflationary models tested against datasets from Planck and WMAP, measuring lensing B-modes connected to large-scale structure studies by SDSS and DES, and characterizing foregrounds similar to analyses undertaken by IRAS and Herschel. Results have contributed to joint analyses with BICEP/Keck, cross-correlations with data from ACT and SPTpol, and parameter constraints relevant to groups at Harvard and Princeton. Science outcomes inform theoretical frameworks developed by researchers associated with Perimeter Institute and Institute for Advanced Study.
Data pipelines incorporate map-making algorithms and component-separation methods related to software used in Planck analysis and simulators developed at NERSC and CITA. Time-ordered data calibration builds on techniques from LIGO and detector characterization methods established at NIST and LBL. Analysis workflows utilize computing resources from centers such as CERN and national supercomputing facilities linked to the European Space Agency and U.S. NSF programs. Cross-checks and null tests draw on methodologies from collaborations like BICEP and SPT.
POLARBEAR-2 is part of an international collaboration including institutions such as the University of Tokyo, KEK, Stanford University, Princeton University, and the Simons Foundation. Financial and logistical support has come from agencies and foundations including the Japan Society for the Promotion of Science, MEXT, NSF, and private foundations tied to astronomy initiatives like the Simons Foundation and philanthropic support channeled through universities such as Harvard and Caltech.
The technological advances from POLARBEAR-2 feed into successor projects and larger arrays, influencing designs for the Simons Observatory, CMB-S4, and instrument concepts reviewed by panels of the National Academies and advisory committees in Japan and the United States. Continued cross-correlation with datasets from Euclid and future missions endorsed by ESA and NASA will refine constraints on inflationary physics and neutrino properties studied by collaborations at CERN and national laboratories. The project's instrumentation heritage propagates through detector fabrication groups at NIST, cryogenics teams at Lawrence Berkeley National Laboratory, and analysis consortia connected to Perimeter Institute.