BICEP2. II. EXPERIMENT AND THREE-YEAR DATA SET

Abstract

We report on the design and performance of the BICEP2 instrument and on its\nthree-year data set. BICEP2 was designed to measure the polarization of the\ncosmic microwave background (CMB) on angular scales of 1 to 5 degrees\n($\\ell$=40-200), near the expected peak of the B-mode polarization signature of\nprimordial gravitational waves from cosmic inflation. Measuring B-modes\nrequires dramatic improvements in sensitivity combined with exquisite control\nof systematics. The BICEP2 telescope observed from the South Pole with a 26~cm\naperture and cold, on-axis, refractive optics. BICEP2 also adopted a new\ndetector design in which beam-defining slot antenna arrays couple to\ntransition-edge sensor (TES) bolometers, all fabricated on a common substrate.\nThe antenna-coupled TES detectors supported scalable fabrication and\nmultiplexed readout that allowed BICEP2 to achieve a high detector count of 500\nbolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree\nangular scales. After optimization of detector and readout parameters, BICEP2\nachieved an instrument noise-equivalent temperature of 15.8 $\\mu$K sqrt(s). The\nfull data set reached Stokes Q and U map depths of 87.2 nK in square-degree\npixels (5.2 $\\mu$K arcmin) over an effective area of 384 square degrees within\na 1000 square degree field. These are the deepest CMB polarization maps at\ndegree angular scales to date. The power spectrum analysis presented in a\ncompanion paper has resulted in a significant detection of B-mode polarization\nat degree scales.\n