A Measurement of the Cosmic Microwave Background B-mode Polarization Power Spectrum at Subdegree Scales from Two Years of polarbear Data

Abstract

We report an improved measurement of the cosmic microwave background B -mode polarization power spectrum with the Polarbear  experiment at 150 GHz. By adding new data collected during the second season of observations (2013–2014) to re-analyzed data from the first season (2012–2013), we have reduced twofold the band-power uncertainties. The band powers are reported over angular multipoles , where the dominant B -mode signal is expected to be due to the gravitational lensing of E -modes. We reject the null hypothesis of no B -mode polarization at a confidence of 3.1 σ  including both statistical and systematic uncertainties. We test the consistency of the measured B -modes with the Λ Cold Dark Matter (ΛCDM) framework by fitting for a single lensing amplitude parameter A L  relative to the Planck  2015 best-fit model prediction. We obtain  ± 0.14(foreground) ± 0.04(multi), where is the fiducial ΛCDM value.