19 August 2014 BICEP2 and Keck array: upgrades and improved beam characterization
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Abstract
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.
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I. Buder, I. Buder, P. A. R. Ade, P. A. R. Ade, Z. Ahmed, Z. Ahmed, R. W. Aikin, R. W. Aikin, K. D. Alexander, K. D. Alexander, M. Amiri, M. Amiri, D. Barkats, D. Barkats, S. J. Benton, S. J. Benton, C. A. Bischoff, C. A. Bischoff, J. J. Bock, J. J. Bock, J. A. Bonetti, J. A. Bonetti, J. A. Brevik, J. A. Brevik, E. Bullock, E. Bullock, B. Burger, B. Burger, B. P. Crill, B. P. Crill, G. Davis, G. Davis, C. D. Dowell, C. D. Dowell, L. Duband, L. Duband, J. P. Filippini, J. P. Filippini, S. Fliescher, S. Fliescher, S. R. Golwala, S. R. Golwala, M. S. Gordon, M. S. Gordon, M. Halpern, M. Halpern, M. Hasselfield, M. Hasselfield, S. R. Hildebrandt, S. R. Hildebrandt, G. C. Hilton, G. C. Hilton, V. V. Hristov, V. V. Hristov, H. Hui, H. Hui, K. D. Irwin, K. D. Irwin, K. S. Karkare, K. S. Karkare, J. P. Kaufman, J. P. Kaufman, B. G. Keating, B. G. Keating, S. Kefeli, S. Kefeli, S. A. Kernasovskiy, S. A. Kernasovskiy, J. M. Kovac, J. M. Kovac, C. L. Kuo, C. L. Kuo, E. M. Leitch, E. M. Leitch, M. Lueker, M. Lueker, P. Mason, P. Mason, K. G. Megerian, K. G. Megerian, C. B. Netterfield, C. B. Netterfield, H. T. Nguyen, H. T. Nguyen, R. O’Brient, R. O’Brient, R. W. Ogburn, R. W. Ogburn, A. Orlando, A. Orlando, C. Pryke, C. Pryke, C. D. Reintsema, C. D. Reintsema, S. Richter, S. Richter, R. Schwarz, R. Schwarz, C. D. Sheehy, C. D. Sheehy, Z. K. Staniszewski, Z. K. Staniszewski, R. V. Sudiwala, R. V. Sudiwala, G. P. Teply, G. P. Teply, K. L. Thompson, K. L. Thompson, J. E. Tolan, J. E. Tolan, A. D. Turner, A. D. Turner, A. G. Vieregg, A. G. Vieregg, A. C. Weber, A. C. Weber, D. V. Wiebe, D. V. Wiebe, P. Wilson, P. Wilson, C. L. Wong, C. L. Wong, K. W. Yoon, K. W. Yoon, } "BICEP2 and Keck array: upgrades and improved beam characterization", Proc. SPIE 9153, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, 915312 (19 August 2014); doi: 10.1117/12.2055713; https://doi.org/10.1117/12.2055713
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