BICEPKeck

BICEPKeck, short for the BICEP/Keck Collaboration, refers to a series of experiments designed to measure the polarization of the cosmic microwave background (CMB) in order to detect primordial gravitational waves predicted by inflationary cosmology. The collaboration operates at the Amundsen-Scott South Pole Station in Antarctica and combines the BICEP (Background Imaging of Cosmic Extragalactic Polarization) and Keck Array instruments. The goal is to observe B-mode polarization signals, which could provide evidence for gravitational waves from the early universe, while distinguishing them from foreground emission such as dust.

The program began with the BICEP experiments and expanded with the Keck Array, a set of co-located receivers that enhanced sensitivity and frequency coverage. The instruments use polarization-sensitive bolometers, including transition-edge sensor detectors, and operate at multiple frequency channels, typically around 100, 150, and 220 GHz. The multi-frequency approach helps separate cosmological signals from polarized foregrounds, a crucial step in interpreting any detected B-modes.

In 2014, BICEP2 announced the detection of B-mode polarization consistent with primordial gravitational waves. However, subsequent analyses, including data from the Keck Array and Planck, indicated that polarized dust emission could account for the observed signal, and no statistically significant evidence for primordial B-modes remained. The collaboration published joint results through late 2010s, providing improved upper limits on the tensor-to-scalar ratio and highlighting the importance of foreground characterization.

Today, BICEPKeck continues to contribute to CMB polarization research, refining measurements across multiple frequencies and coordinating with other experiments to constrain models of inflation. The work underscores the challenges of foreground contamination and the need for precise, multi-frequency observations in the quest to detect primordial gravitational waves.