GroundBIRD: A CMB Polarization Experiment with MKID Arrays

GroundBIRD is a ground-based experiment for a precise observation of the cosmic microwave background (CMB) polarizations. To achieve high sensitivity at large angular scales, we adopt three features in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID), and cold optics. The rotation scanning strategy has the advantage to suppress 1/f noise. It also provides a large sky coverage of 40%, which corresponds to the large angular scales of $$l \sim 6$$ . This allows us to constrain the tensor-to-scalar ratio by using low l B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 145 GHz and 23 are for 220 GHz. This array is currently under development, and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment.