A Measurement of the Degree-scale CMB B-mode Angular Power Spectrum with POLARBEAR

Abstract

We present a measurement of theB-mode polarization power spectrum of the cosmic microwave background (CMB) using data taken from 2014 July to 2016 December with thePolarbearexperiment. The CMB power spectra are measured using observations at 150 GHz with an instantaneous array sensitivity of<CDATA<ion a 670 square degree patch of sky centered at (R.A., decl.) = (+0(h)12(m)0(s), -59 degrees 18 '). A continuously rotating half-wave plate is used to modulate polarization and to suppress low-frequency noise. We achieve 32 mu K arcmin effective polarization map noise with a knee in sensitivity ofl = 90, where the inflationary gravitational-wave signal is expected to peak. The measuredB-mode power spectrum is consistent with a ?CDM lensing and single dust component foreground model over a range of multipoles 50 <= l <= 600. The data disfavor zero sigma using thisl range ofPolarbeardata alone. We cross-correlate our data with Planck full mission 143, 217, and 353 GHz frequency maps and find the low-l B-mode power in the combined data set to be consistent with thermal dust emission. We place an upper limit on the tensor-to-scalar ratior < 0.90 at the 95% confidence level after marginalizing over foregrounds.