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Phys Rev Lett. 2014 Jun 20;112(24):241101. Epub 2014 Jun 19.

Detection of B-mode polarization at degree angular scales by BICEP2.

Author information

1
School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom.
2
Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
3
Joint ALMA Observatory, Vitacura, Santiago, Chile.
4
Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada.
5
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 42, Cambridge, Massachusetts 02138, USA.
6
Department of Physics, California Institute of Technology, Pasadena, California 91125, USA and Jet Propulsion Laboratory, Pasadena, California 91109, USA.
7
Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
8
Jet Propulsion Laboratory, Pasadena, California 91109, USA.
9
Service des Basses Températures, Commissariat à l'Energie Atomique, 38054 Grenoble, France.
10
Department of Physics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
11
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.
12
National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
13
National Institute of Standards and Technology, Boulder, Colorado 80305, USA and Department of Physics, Stanford University, Stanford, California 94305, USA and Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
14
Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
15
Department of Physics, Stanford University, Stanford, California 94305, USA.
16
Department of Physics, Stanford University, Stanford, California 94305, USA and Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
17
University of Chicago, Chicago, Illinois 60637, USA.
18
Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada and Canadian Institute for Advanced Research, Toronto, Ontario, M5G 1Z8, Canada.
19
Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA and Department of Physics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
20
Department of Physics, University of Minnesota, Minneapolis, Minnesota 55455, USA and University of Chicago, Chicago, Illinois 60637, USA.
21
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 42, Cambridge, Massachusetts 02138, USA and University of Chicago, Chicago, Illinois 60637, USA.

Abstract

We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around ℓ∼80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of ≈300  μK(CMB)√s. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of B-mode power over the base lensed-ΛCDM expectation in the range 30 < ℓ < 150, inconsistent with the null hypothesis at a significance of >5σ. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power ∼(5-10)× smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3σ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at 1.7σ. The observed B-mode power spectrum is well fit by a lensed-ΛCDM+tensor theoretical model with tensor-to-scalar ratio r = 0.20_(-0.05)(+0.07), with r = 0 disfavored at 7.0σ. Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets.

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