Bicep2. Ii. Experiment and Three-Year Data Set

Abstract

We report on the design and performance of the Bicep2 instrument and on its three-year data set. Bicep2 was designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 1 •-5 • (= 40-200), near the expected peak of the B-mode polarization signature of primordial gravitational waves from cosmic inflation. Measuring B-modes requires dramatic improvements in sensitivity combined with exquisite control of systematics. The Bicep2 telescope observed from the South Pole with a 26 cm aperture and cold, on-axis, refractive optics. Bicep2 also adopted a new detector design in which beam-defining slot antenna arrays couple to transition-edge sensor (TES) bolometers, all fabricated on a common substrate. The antenna-coupled TES detectors supported scalable fabrication and multiplexed readout that allowed Bicep2 to achieve a high detector count of 500 bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree angular scales. After optimization of detector and readout parameters, Bicep2 achieved an instrument noise-equivalent temperature of 15.8 μK √ s. The full data set reached Stokes Q and U map depths of 87.2 nK in square-degree pixels (5. 2 μK) over an effective area of 384 deg 2 within a 1000 deg 2 field. These are the deepest CMB polarization maps at degree angular scales to date. The power spectrum analysis presented in a companion paper has resulted in a significant detection of B-mode polarization at degree scales.

Inflation and String Theory

“…Joint constraints for a quadratic potential.-In the important special case where V (φ) = 1 2 m 2 φ 2 , the above results can be combined to place strong limits on the model parameters [243] (see also [722] 139) where the inequality uses the Planck upper limits on r and f equil NL . Because ∆ 2 R (k ) = 2.2 × 10 −9 , we conclude that…”

“…There are many experiments looking for B-modes on degree scales, including KeckArray [139], EBEX [140], SPIDER [141], ABS [142], and CLASS [143]); and on arcminute scales, including POLARBEAR [144], SPTpol [145], and ACTpol [146]). Finally, given the size of the signal seen by the BICEP2 collaboration, the Planck satellite has a chance to see the reionization peak in the B-mode spectrum at low .…”

The powers of monodromy

“…In particular, in the context of inflation [2][3][4][5], an observation of a tensor-to-scalar ratio r 10 −2 implies an unprecedented connection between empirical observations and quantum gravity, for two reasons: it provides a measurement of the quantum mechanical variance of the tensor modes of the metric [6][7][8][9][10][11][12][13], and it indicates a super-Planckian field excursion [14,15]. An impressive variety of observational efforts are approaching the sensitivity required to detect r in this range [16], with a recent report of a detection of B-mode polarization [17,18] that may contain a signal of primordial origin corresponding to inflationary tensor modes [19,20], depending on the outcome of important foreground measurements generalizing [21,22].…”

Survey strategy optimization for the Atacama Cosmology Telescope

“…1 Polarization measurements can provide important additional information able to break degeneracies between cosmological parameters and constrain extensions of the ΛCDM model, such as the tensor-to-scalar ratio r and the neutrino mass sum m ν . Several ground based experiments, such as the Atacama Cosmology Telescope Polarimeter (ACTPol), 2 POLARBEAR, 3 SPTpol, 4 BICEP2, 5 Keck-array 6 and CLASS, 7 are measuring the E-mode and B-mode polarization signals.…”