BICEP2 and Keck Array: upgrades and improved beam characterization

• Published in: SPIE Proceedings, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII
• Main Authors: Zmuidzinas, Jonas, Buder, I., Ade, Peter A. R., Ahmed, Z., Aikin, R. W., Alexander, K. D., Amiri, M., Barkats, D., Benton, S. J., Bischoff, C. A., Bock, J. J., Bonetti, J. A., Brevik, J. A., Bullock, E., Burger, B., Crill, B. P., Davis, G., Dowell, C. D., Duband, L., Filippini, J. P., Fliescher, S., Golwala, S. R., Gordon, M. S., Halpern, M., Hasselfield, M., Hildebrandt, S. R., Hilton, G. C., Hristov, V. V., Hui, H., Irwin, K. D., Karkare, K. S., Kaufman, J. P., Keating, B. G., Kefeli, S., Kernasovskiy, S. A., Kovac, J. M., Kuo, C. L., Leitch, E. M., Lueker, M., Mason, P., Megerian, K. G., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Orlando, A., Pryke, C., Reintsema, C. D., Richter, S., Schwarz, R.
• Format: Conference Object
• Language: unknown
• Published: Society of Photo-optical Instrumentation Engineers 2014
• Subjects: QB Astronomy; South Pole; South pole
• Online Access: https://orca.cardiff.ac.uk/id/eprint/89799/; https://doi.org/10.1117/12.2055713

Searching for evidence of inflation by measuring B-modes in the cosmic microwave background (CMB) polarization at degree angular scales remains one of the most compelling experimental challenges in cosmology. BICEP2 and the Keck Array are part of a program of experiments at the South Pole whose main goal is to achieve the sensitivity and systematic control necessary for measurements of the tensor-to-scalar ratio at σ(r) ~0:01. Beam imperfections that are not sufficiently accounted for are a potential source of spurious polarization that could interfere with that goal. The strategy of BICEP2 and the Keck Array is to completely characterize their telescopes' polarized beam response with a combination of in-lab, pre-deployment, and on-site calibrations. We Sereport the status of these experiments, focusing on continued improved understanding of their beams. Far-field measurements of the BICEP2 beam with a chopped thermal source, combined with analysis improvements, show that the level of residual beam-induced systematic errors is acceptable for the goal of σ(r) ~ 0:01 measurements. Beam measurements of the Keck Array side lobes helped identify a way to reduce optical loading with interior cold baffles, which we installed in late 2013. These baffles reduced total optical loading, leading to a ~ 10% increase in mapping speed for the 2014 observing season. The sensitivity of the Keck Array continues to improve: for the 2013 season it was 9:5 μK _/s noise equivalent temperature (NET). In 2014 we converted two of the 150-GHz cameras to 100 GHz for foreground separation capability. We have shown that the BICEP2 and the Keck Array telescope technology is sufficient for the goal of σ(r) ~ 0:01 measurements. Furthermore, the program is continuing with BICEP3, a 100-GHz telescope with 2560 detectors. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.