Collaborative Research: Science Observation with BICEP3 CMB Polarization Experiment

Harvard University, Cambridge MA

Investigators

Abstract

Evidence is mounting that the entire observable Universe was spawned in a dramatic superluminal "Inflation" of a sub-nuclear volume. This violent acceleration of matter would have produced a cosmic gravitational-wave background (CGB), the amplitude of which measures the energy scale of Inflation. The CGB imprints a faint signature in the polarization of the Cosmic Microwave Background (CMB) with an amplitude parameterized by the ratio of tensor to scalar modes, r = T/S. Many slow-roll models of Inflation produce r ~ 0.01?0.1, corresponding to peak CMB fluctuations of 30?100 nK rms on degree angular scales. Detecting the polarization signature of the CGB is arguably the most important goal in cosmology today. The Astro2010 Decadal Survey described the search for the CGB as "the most exciting quest of all", and emphasized that "mid-term investment is needed for systems aimed at detecting the (B-mode) polarization of the CMB". In 2005, the Task Force on CMB Research identified this as the highest priority for the field and established a target sensitivity of r = 0.02. The ongoing BICEP/BICEP2/SPUD series of experiments is dedicated to this science goal. They began operating at the South Pole Station (Antarctica) in 2006 and are relentlessly mapping an 800-deg2 region of the sky that uniquely low in Galactic foregrounds - the so-called Southern Hole. The combined sensitivity at 150 GHz (now greater than that of the Planck spacecraft) is concentrated on the Southern Hole increasing the ability to detect the CGB significantly. This award will support for three years the science observations and analysis with a new CMB polarimeter called BICEP3 - a third-generation compact refractor that will represent another breakthrough in per-receiver sensitivity. BICEP3 provides a further ten-fold increase in optical throughput compared to a single BICEP2/SPUD receiver. Populated with 2560 TESs at 95 GHz over three years of observing, BICEP3 will produce the most sensitive degree-scale CMB polarization maps of 95 GHz of any current or planned experiment. BICEP3 observations, when combined with SPUD's deep 150 GHz and 220 GHz coverage, will provide significantly more powerful discrimination between CMB polarization and Galactic foregrounds. Detection of the CGB would be to Inflation what the discovery of the CMB was to the Big Bang. Indeed its impact might be even broader, as Inflation directly bears on the current frontiers of fundamental physics. The project will continue to provide excellent training for undergraduate and graduate students, as well as postdoctoral fellows (including those from underrepresented groups) in laboratories that have exceptional track records in this regard. Cosmology and research in Antarctica both capture the public imagination, making this combination a remarkably effective vehicle for stimulating interest in science.