The POLARBEAR Cosmic Microwave Background Polarization Experiment

The polarbear cosmic microwave background (CMB) polarization experiment has been observing since early 2012 from its 5,200 m site in the Atacama Desert in Northern Chile. polarbear ’s measurements will characterize the expected CMB polarization due to gravitational lensing by large scale structure, and search for the possible B-mode polarization signature of inflationary gravitational waves. polarbear ’s 250 mK focal plane detector array consists of 1,274 polarization-sensitive antenna-coupled bolometers, each with an associated lithographed band-defining filter and contacting dielectric lenslet, an architecture unique in current CMB experiments. The status of the polarbear instrument, its focal plane, and the analysis of its measurements are presented.