GroundBIRD: an experiment for CMB polarization measurements at a large angular scale from the ground

Abstract

Odd-parity patterns in the cosmic microwave background (CMB) polarization, <i>B</i>-modes, could provide important cosmological information. Detection of the primordial <i>B</i>-mode power at a large angular scale would be a smoking gun signature of the inflationary universe. In particular, detecting a reionization bump (at a multipole of &le; 10) should be a clear evidence of it. GroundBIRD is designed to detect the <i>B</i>-mode signal at this large angular scale from the ground. We will use superconducting detector arrays with small telescope that will also be cooled down to 4K. Therefore, the basic design can be extended to a satellite experiment. GroundBIRD employs a high-speed (20 rpm) rotation scan instead of the usual left–right azimuthal scan; this allows us to maintain a high-speed scan without any deceleration, resulting in a significant expansion of the scan range to 60&deg; without any effect of the detector 1/<i>f</i> noise. Our target is measuring the CMB polarization power in a multipole (<i>l</i>) range of 6 &le; <i>l</i> &le; 300. We plan to start commissioning the instruments in Japan in early 2014; they will then be moved to the Atacama Desert in Chile for scientific observations.