Initial Performance of BICEP3: A Degree Angular Scale 95 GHz Band Polarimeter

TL;DR

BICEP3 is a new 95 GHz polarimeter with a 550mm aperture designed to measure CMB polarization at degree scales, aiming to improve constraints on inflationary gravitational waves.

Contribution

This paper reports the initial deployment and performance of BICEP3, a significantly upgraded instrument enhancing the BICEP/Keck program's mapping speed and sensitivity.

Findings

Successfully deployed and characterized BICEP3 at the South Pole.

Achieved initial observations with 9 detector tiles, aiming for full capacity of 20.

Projected to set upper limits on the tensor-to-scalar ratio r ≤ 0.03.

Abstract

BICEP3 is a $550~mm$ aperture telescope with cold, on-axis, refractive optics designed to observe at the $95~GHz$ band from the South Pole. It is the newest member of the BICEP/Keck family of inflationary probes specifically designed to measure the polarization of the cosmic microwave background (CMB) at degree-angular scales. BICEP3 is designed to house 1280 dual-polarization pixels, which, when fully-populated, totals to $\sim$9$\times$ the number of pixels in a single Keck $95~GHz$ receiver, thus further advancing the BICEP/Keck program's $95~GHz$ mapping speed. BICEP3 was deployed during the austral summer of 2014-2015 with 9 detector tiles, to be increased to its full capacity of 20 in the second season. After instrument characterization measurements were taken, CMB observation commenced in April 2015. Together with multi-frequency observation data from Planck, BICEP2, and the Keck Array, BICEP3 is projected to set upper limits on the tensor-to-scalar ratio to $r$ $\lesssim 0.03$ at $95\%$ C.L..