Analysis of Temperature-to-Polarization Leakage in BICEP3 and Keck CMB Data from 2016 to 2018

The BICEP/Keck Array experiment is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background polarization from the South Pole in search of a primordial Bmode signature. As a pair differencing experiment, an important systematic that must be controlled is the differential null response between the co-located, orthogonally polarized detectors. We use high-fidelity, in-situ measurements of the null...