Optical characterization of the Keck Array and BICEP3 CMB Polarimeters from 2016 to 2019
Abstract
The BICEP/Keck experiment (BK) is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background (CMB) polarization from the South Pole in search of a primordial -mode signature. This -mode signal arises from primordial gravitational waves interacting with the CMB, and has amplitude parametrized by the tensor-to-scalar ratio . Since 2016, BICEP3 and the Keck Array have been observing with 4800 total antenna-coupled transition-edge sensor detectors, with frequency bands spanning 95, 150, 220, and 270 GHz. Here we present the optical performance of these receivers from 2016 to 2019, including far-field beams measured in situ with an improved chopped thermal source and instrument spectral response measured with a field-deployable Fourier Transform Spectrometer. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We generate per-detector far-field beam maps and the corresponding differential beam mismatch that is used to estimate the temperature-to-polarization leakage in our CMB maps and to give feedback on detector and optics fabrication. The differential beam parameters presented here were estimated using improved low-level beam map analysis techniques, including efficient removal of non-Gaussian noise as well as improved spatial masking. These techniques help minimize systematic uncertainty in the beam analysis, with the goal of constraining the bias on induced by temperature-to-polarization leakage to be subdominant to the statistical uncertainty. This is essential as we progress to higher detector counts in the next generation of CMB experiments.
Keywords
Cite
@article{arxiv.2002.05197,
title = {Optical characterization of the Keck Array and BICEP3 CMB Polarimeters from 2016 to 2019},
author = {Keck Collaboration and T. St Germaine and P. A. R. Ade and Z. Ahmed and M. Amiri and D. Barkats and R. Basu Thakur and C. A. Bischoff and J. J. Bock and H. Boenish and E. Bullock and V. Buza and J. Cheshire and J. Connors and J. Cornelison and M. Crumrine and A. Cukierman and M. Dierickx and L. Duband and S. Fatigoni and J. P. Filippini and S. Fliescher and J. A. Grayson and G. Hall and M. Halpern and S. Harrison and S. R. Hildebrandt and G. C. Hilton and H. Hui and K. D. Irwin and J. Kang and K. S. Karkare and E. Karpel and S. Kefeli and S. A. Kernasovskiy and J. M. Kovac and C. L. Kuo and K. Lau and E. M. Leitch and K. G. Megerian and L. Moncelsi and T. Namikawa and C. B. Netterfield and H. T. Nguyen and R. O'Brient and R. W. Ogburn and S. Palladino and C. Pryke and B. Racine and C. D. Reintsema and S. Richter and A. Schillaci and R. Schwarz and C. D. Sheehy and A. Soliman and B. Steinbach and R. V. Sudiwala and K. L. Thompson and J. E. Tolan and C. Tucker and A. D. Turner and C. Umilta and A. G. Vieregg and A. Wandui and A. C. Weber and D. V. Wiebe and J. Willmert and C. L. Wong and W. L. K. Wu and E. Yang and K. W. Yoon and E. Young and C. Yu and C. Zhang},
journal= {arXiv preprint arXiv:2002.05197},
year = {2020}
}
Comments
8 pages, 3 figures. Accepted by the Journal of Low Temperature Physics (Proceedings of the 18th International Workshop on Low Temperature Detectors)