Background Imaging of Cosmic Extragalactic Polarization ( Bicep ) is a bolometric polarimeter designed to measure the inflationary B -mode polarization of the cosmic microwave background ( CMB ) at degree angular scales .
During three seasons of observing at the South Pole ( 2006 through 2008 ) , Bicep mapped \sim 2 \% of the sky chosen to be uniquely clean of polarized foreground emission .
Here , we present initial results derived from a subset of the data acquired during the first two years .
We present maps of temperature , Stokes Q and U , E and B modes , and associated angular power spectra .
We demonstrate that the polarization data are self-consistent by performing a series of jackknife tests .
We study potential systematic errors in detail and show that they are sub-dominant to the statistical errors .
We measure the E -mode angular power spectrum with high precision at 21 \leq \ell \leq 335 , detecting for the first time the peak expected at \ell \sim 140 .
The measured E -mode spectrum is consistent with expectations from a \Lambda CDM model , and the B -mode spectrum is consistent with zero .
The tensor-to-scalar ratio derived from the B -mode spectrum is r = 0.02 ^ { +0.31 } _ { -0.26 } , or r < 0.72 at 95 % confidence , the first meaningful constraint on the inflationary gravitational wave background to come directly from CMB B -mode polarization .