POLARBEAR-2: a new CMB polarization receiver system for the Simons array (Conference Presentation)

POLARBEAR-2 is a new receiver system, which will be deployed on the Simons Array telescope platform, for the measurement of Cosmic Microwave Background (CMB) polarization. The science goals with POLARBEAR-2 are to characterize the B-mode signal both at degree and sub-degree angular-scales. The degree-scale polarization data can be used for quantitative studies on inflation, such as the reconstruction of the energy scale of inflation. The sub-degree polarization data is an excellent tracer of large-scale structure in the universe, and will lead to precise constraints on the sum of the neutrino masses. In order to achieve these goals, POLARBEAR-2 employs 7588 polarization-sensitive antenna-coupled transition-edge sensor (TES) bolometers on the focal plane cooled to 0.27K with a three-stage Helium sorption refrigerator, which is ~6 times larger array over the current receiver system. The large TES bolometer array is read-out by an upgraded digital frequency-domain multiplexing system capable of multiplexing 40 bolometers through a single superconducting quantum interference device (SQUID). The first POLARBEAR-2 receiver, POLARBEAR-2A is constructed and the end-to-end testing to evaluate the integrated performance of detector, readout, and optics system is being conducted in the laboratory with various types of test equipments. The POLARBEAR-2A is scheduled to be deployed in 2018 at the Atacama desert in Chile. To further increase measurement sensitivity, two more POLARBEAR-2 type receivers will be deployed soon after the deployment (Simons Array project). The Simons Array will cover four frequency bands at 95GHz, 150GHz, 220GH and 270GHz for better control of the foreground signal. The projected constraints on a tensor-to-scalar ratio (amplitude of inflationary B-mode signal) is σ(r=0.1) = $6.0 \times 10^{-3}$ after foreground removal ($4.0 \times 10^{-3}$ (stat.)), and the sensitivity to the sum of the neutrino masses when combined with DESI spectroscopic galaxy survey data is 40 meV at 1-sigma after foreground removal (19 meV(stat.)). We will present an overview of the design, assembly and status of the laboratory testing of the POLARBEAR-2A receiver system as well as the Simons Array project overview.