FIRST SEASON QUIET OBSERVATIONS : MEASUREMENTS OF CMB POLARIZATION POWER SPECTRA AT 43 GHZ IN THE MULTIPOLE RANGE 25 ≤ l ≤ 475 QUIET Collaboration —

The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and 95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the CMB. QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, over 10,000hours of data were collected, first with the 19-element 43-GHz array (3458hours) and then with the 90-element 95-GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ≈ 1000 square degrees. This paper reports initial results from the 43-GHz receiver which has an array sensitivity to CMB fluctuations of 69μK √ s. The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB, and EB power spectra in the multipole range l = 25–475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3-σ significance, the E-mode spectrum is consistent with the ΛCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r = 0.35 −0.87. The combination of a new time-stream “double-demodulation” technique, side-fed Dragonian optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r = 0.1. Subject headings: cosmic background radiation—Cosmology: observations—Gravitational waves— inflation—Polarization 1 Kavli Institute for Cosmological Physics, Department of Physics, Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA; send correspondence to A. Kusaka, akito@kicp.uchicago. edu 2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany 3 High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 4 Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan 5 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E. California Blvd M/C 249-17, Pasadena, CA 91125, USA 6 Department of Physics and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA 7 Department of Physics, University of Miami, 1320 Campo Sano Drive, Coral Gables, FL 33146, USA 8 Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, Norway 9 Department of Physics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway 10 Department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK 11 Oxford Martin School, 34 Broad Street, Oxford OX1 3BD, UK 12 Department of Physics and Astronomy, University College London, Gower Street, London WC1E, UK 13 Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile 14 Departamento de Astronomı́a, Universidad de Concepción, Casilla 160-C, Concepción, Chile 15 Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Varian Physics Building, 382 Via Pueblo Mall, Stanford, CA 94305, USA 16 Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK 17 Centre of Mathematics for Applications, University of Oslo, P.O. Box 1053 Blindern, N-0316 Oslo, Norway 18 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA 91109 19 Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, MI 48109, USA 20 Fermi National Accelerator Laboratory, Batavia, IL 60510, USA 21 Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA 22 Current address: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 43, Cambridge, MA 02138, USA 23 Current address: Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA 24 Current address: Micro Encoder Inc., Kirkland, WA 98034, USA 2 The QUIET Collaboration