The CMB Polarization Observation Experiment GroundBIRD
University of Tsukuba
The Cosmic Microwave Background Radiation (CMB), the afterglow of the Big Bang that has expanded with the evolution of the universe, contains 13.8 billion years of history. Currently, studies on the detailed observation of the CMB polarization fluctuation patterns are attracting a great deal of attention. Many research groups are working to achieve new results from polarized light observations, such as the discovery of primordial gravitational waves, which provide evidence for inflationary cosmology, and the first measurement of neutrino mass sums. GroundBIRD is an ambitious project to observe the sky at an extraordinary speed to realize CMB polarization observations over a wide sky area, which has never been achieved on the ground. GroundBIRD will measure the optical thickness of the cosmic re>ionization phase by observing the E-mode polarization pattern intensity over a large angular region for three years. This parameter is strongly correlated with the sum of neutrino masses, and independent measurement of the optical thickness during the cosmic reionization period will improve the accuracy of the determination of the sum of neutrino masses. In this talk, I will give an overview of CMB polarimetry, introduce the GroundBIRD telescope, and present our research on the optical thickness measurement of the cosmic reionization phase. Figure. Simulated GroundBIRD maps map (145 GHz band). From K. Lee et al. (2021) ApJ 915 88.