BICEP Array

BICEP Array
Name	BICEP Array
Type	Ground-based microwave polarimeter
Location	South Pole Station
Wavelength	Millimeter

BICEP Array is a ground-based microwave polarimeter deployed at the South Pole Station to measure the polarization of the cosmic microwave background (CMB). The project seeks to detect or constrain primordial gravitational waves from cosmic inflation by observing degree-scale B-mode polarization patterns in the CMB. BICEP Array continues a program of instruments following the BICEP2 and Keck Array experiments, integrating advances in detector technology, cryogenics, and readout systems.

Overview

BICEP Array is part of a lineage including BICEP1, BICEP2, Keck Array, and the South Pole Telescope program, operating from the Amundsen–Scott South Pole Station on the Antarctic plateau. The experiment is principally associated with teams from institutions such as the California Institute of Technology, Harvard University, Stanford University, and Cardiff University, and it collaborates with initiatives like the Planck (spacecraft), WMAP, and proposed projects including CMB-S4. The instrument targets multipole ranges sensitive to inflationary tensor modes first predicted in models by Alan Guth, Andrei Linde, and Alexei Starobinsky, while also constraining foregrounds such as polarized dust traced by observations from Planck Collaboration and synchrotron emission mapped by experiments like WMAP and QUIJOTE CMB Experiment.

Instrument Design and Detectors

The BICEP Array comprises multiple cryostats each housing focal planes of transition-edge sensor (TES) bolometers coupled to planar antenna arrays and coupled optics derived from designs used in BICEP2 and the Keck Array. Detector fabrication relies on facilities and expertise at institutions including Jet Propulsion Laboratory (JPL), NIST, and university cleanrooms such as those at Caltech and Stanford University. Readout employs superconducting quantum interference device (SQUID) multiplexing techniques developed in concert with groups at NIST, Brookhaven National Laboratory, and SLAC National Accelerator Laboratory. The optics include refracting lenses, anti-reflection coatings, and cold stops similar to those used in POLARBEAR and ACT (Atacama Cosmology Telescope), while cryogenic systems leverage pulse-tube and sorption-cooler technology akin to hardware deployed in SPTpol.

Observing Strategy and Site

Observations are conducted from the Amundsen–Scott South Pole Station, chosen for its high altitude, low precipitable water vapor, and stable atmosphere, attributes also exploited by the South Pole Telescope (SPT) and earlier CMB programs like DASI and Python (telescope). The scanning strategy emphasizes deep integration on low-foreground regions of the southern sky used previously by BICEP2 and Keck Array, with coordinated multi-frequency coverage to separate Galactic polarized dust emission characterized by Planck Collaboration and synchrotron components constrained by surveys including S-PASS and Haslam map. Logistics and support involve collaboration with the United States Antarctic Program and infrastructure shared with observatories such as the IceCube Neutrino Observatory.

Data Analysis and Systematics

Data processing pipelines build on analysis frameworks developed in prior experiments like BICEP2, Keck Array, and Planck (spacecraft), combining map-making, power-spectrum estimation, and likelihood analyses. Foreground separation integrates external templates and component-separation methods informed by analyses from the Planck Collaboration and cross-correlation techniques used with datasets from WMAP and SPTpol. Systematic error control addresses instrumental polarization, beam asymmetries, gain calibration, and bandpass mismatches; mitigation strategies echo approaches from POLARBEAR, ACT, and SPTpol, including jackknife tests, null tests, and end-to-end simulations developed with computational resources at institutions like NERSC and CERN. Ancillary calibration uses celestial sources such as Jupiter and the Crab Nebula (Tau A), and ties to absolute temperature scales established by measurements from COBE and WMAP.

Scientific Results and Constraints

BICEP Array aims to improve constraints on the tensor-to-scalar ratio r, refining limits set by combined analyses of BICEP2/Keck Array and Planck Collaboration data. The program also measures lensing B-modes, constrains cosmological parameters in conjunction with datasets from Planck (spacecraft), WMAP, and ACT, and characterizes polarized Galactic foregrounds relevant to models by Draine & Lazarian and studies of interstellar magnetic fields traced by Planck Collaboration. Results inform theoretical work by researchers including Alan Guth, Andrei Linde, and Viatcheslav Mukhanov, and contribute to forecasts and design choices for next-generation facilities like CMB-S4 and proposed space missions such as LiteBIRD.

Collaborations and Operations

The BICEP Array collaboration comprises scientists, engineers, and institutions including California Institute of Technology, Harvard University, Stanford University, Cardiff University, University of Chicago, Kavli Institute for Particle Astrophysics and Cosmology, Jet Propulsion Laboratory (JPL), and national laboratories such as Brookhaven National Laboratory and SLAC National Accelerator Laboratory. Operations involve coordination with the United States Antarctic Program and the National Science Foundation (United States), while data releases and joint analyses are often performed alongside teams from the Planck Collaboration, SPT, and ACT. The collaboration maintains ties to broader cosmology efforts and workshops such as meetings organized by the Kavli Institute for Theoretical Physics and the Perimeter Institute.

Category:Cosmic microwave background experiments