The B icep 2 and Keck Array experiments are designed to measure the polarization of the cosmic microwave background ( CMB ) on angular scales of 2-4 degrees ( \ell = 50 –100 ) .
This is the region in which the B -mode signal , a signature prediction of cosmic inflation , is expected to peak .
B icep 2 was deployed to the South Pole at the end of 2009 and is in the middle of its third year of observing with 500 polarization-sensitive detectors at 150 ~ { } \mathrm { GHz } .
The Keck Array was deployed to the South Pole at the end of 2010 , initially with three receivers—each similar to B icep 2 .
An additional two receivers have been added during the 2011-12 summer .
We give an overview of the two experiments , report on substantial gains in the sensitivity of the two experiments after post-deployment optimization , and show preliminary maps of CMB polarization from B icep 2 .