Clover - Measuring the Cosmic Microwave Background B-mode Polarization

Clover is a UK-led experiment to measure the Bmode polarization of the cosmic microwave background. The instruments are currently under construction and deployment to the Pampa La Bola site in the Atacama Desert is planned for 2010. It consists of two 2-m class telescopes feeding background limited imaging arrays of ~100 dual polarization pixels at each of 97, 150 and 225 GHz. The waveguide and antenna fed TES bolometers are limited by unavoidable photon noise from the atmosphere, and read-out using NIST’s time domain multiplexing scheme. The entire instrument has been designed for exceptionally low systematic errors in polarization measurements, which has necessitated novel designs for the instrument optics, horn arrays, OMTs and detector feeds, as well as careful development of the scan strategy, field location and data analysis methods. The experiment aims to measure the polarization of the CMB with an angular resolution of 5.5′ − 8′ across 1000 deg2 of sky(angular multipole range 20 < l < 1000) to a sensitivity of 8 μK-arcmin after foreground cleaning. If all systematics are adequately controlled this will allow the detection of the primordial B-mode CMB anisotropies down to tensor to scalar ratios of 0.03, as well as providing extremely accurate measurements of the CMB temperature, E-mode polarization, and B-mode lensing polarization. Detecting or constraining the level of the primordial B-mode signal will allow constraints to be placed on the energy scale of inflation, providing an unprecedented insight into the physics of the early Universe. We describe the current status of the Clover project, including the current instrument design and construction status, and the development of the novel technology involved.