Astronomy seminar: "Measurements of Degree-Scale B-mode Polarization with the BICEP/Keck Experiments at South Pole"

Benjamin Racine, Harvard-Smithsonian Center for Astrophysics
- | David Rittehouse Laboratory, A6

The BICEP and Keck experiments, located at the South Pole, are currently observing the polarized microwave sky at the degree scale using refractive telescopes. They are searching for a signature of primordial gravitational waves in the so-called B modes of the cosmic microwave background (CMB), parametrized with the tensor-to-scalar ratio r. In this talk I will introduce our latest analysis which includes BICEP2 and Keck array data up to the end of 2015. These are the deepest CMB polarization maps to date at 95, 150 and for the first time 220GHz. We use these multiple frequency channels in combination with Planck and WMAP data to constrain a model consisting of the lensed-LCDM + r, Galactic dust and synchrotron, which yields r<0.07 at 95% confidence. I will give an update on the subsequent observations from BICEP3 and the Keck array which took place since 2016, and provided more data at 95, 150, 220 and a new 270GHz channel. I will then review the ongoing developments of BICEP Array (BA), the stage 3 upgrade, which will observe with 40,000 detectors, ranging from 30 to 270GHz. BA will improve the sensitivity to the primordial B-mode signal by one order of magnitude. I will conclude with CMB Stage 4 (S4), an ambitious future program with up to half a million detectors, that will observe from South Pole and Chile.