CMB Stage 4

CMB Stage 4 (CMB-S4) was a proposed ground-based mm-wave observatory to search for gravitational waves from cosmic inflation, test for the presence of new light relativistic particles in the early universe, measure the total mass in the neutrino sector, constrain a variety of dark matter and dark energy models, map matter throughout the cosmos using gravitational lensing of the CMB, and conduct a unique wide-field time-domain survey in the millimeter band. CMB-S4 was canceled in the design stage, but had been slated to receive joint support from the DOE and NSF. It was the highest-ranked new project recommended by the decadal survey of US particle physics by the Particle Physics Project Prioritization Panel, and it was also recommended as a "high priority" new project by the decadal survey of US astronomy and astrophysics by the National Academies of Engineering, Science, and Medicine. The observatory would have been sensitive to wavelengths from 20 GHz to 300 GHz with ~500,000 detectors across a combination of large-aperture (~6 meter) and small-aperture (~0.5 meter) telescopes.

Our group's work on CMB-S4 centered on the design of its small-aperture telescopes, which would provide ultra-deep maps of ~5% of the sky with sensitivity to degree-scale polarization anisotropies of the CMB in order to search for signatures of cosmic inflation.  We planned to integrate and test many of the small aperture telescopes at LBNL before shipping them to remote millimeter-wave observing sites at high elevation.

Learn more about the observatory through its public website.