Collaborative Research: Next Generation CMB Polarization Measurements withthe QUEST Experiment on DASI

California Institute Of Technology, Pasadena CA

Investigators

Abstract

The proposal is to deploy the QUEST experiment to the South Pole Station and to operate it over two austral winter seasons. The receiver and optics are already separately funded and under construction. The telescope will be mounted on the existing DASI platform, covering most of the cost of doing so using existing funds, and re-using large parts of the DASI infrastructure and control system, making this a highly leveraged proposal. QUEST is a 2.6-m Cassegrain telescope equipped with a next generation polarization-sensitive bolometer array, which will be aimed on obtaining maps of the Cosmic Microwave Background (CMB) polarization with unprecedented sensitivity and angular resolution. The polarization of the CMB results from bulk motions of material at the time of the plasma-neutral transition and the polarization measurements are the next frontier of CMB research, offering both the opportunity to make crucial tests of the standard cosmological model, and fresh insights which will lead beyond it. Angular scale in CMB studies is customarily referred to by spherical multipole number l, and the polarization pattern decomposed into so-called E-modes and B-modes. DASI was the first experiment to detect E-mode polarization at l ~ 300. More recently WMAP has released results on the T-E cross-correlation extending down to low multipoles and providing important new information on the reionization of the Universe. At this time a battery of experiments are either running or under construction to improve CMB polarization measurements. The experiment proposed here (which is referred below as "QUEST and DASI", or QUaD) will go well beyond these and is a true "next generation" instrument. QUaD has raw sensitivity similar to the planned Planck space mission, and in fact shares much of the same technology. However, while Planck plans to survey the whole sky, QUaD will go extremely deep on small patches selected for extremely low foreground contamination. This is the crucial difference between the two experiments - not simply that QUaD will come first by at least several years. QuaD's maps will have dramatically higher signal to noise per pixel. As the sensitivity is pushed down to microkelvin level and the multipoles up to 2000 and beyond, such maps will prove crucial to disentangling the cosmic signal from instrumental and foreground effects. In this way, it is expected that the QUaD maps will be relevant for extending through the Planck era to that of a possible polarimeter on the South Pole (8-m) Telescope and the CMBpol space mission currently under discussion. In the same way that DASI and CBI make complementary temperature measurements over different ranges in l space, BICEP and QUaD will make complementary polarization measurements. B-mode polarization at higher multipoles is confidently expected from lensing of the E-mode pattern by intervening large-scale structure. QUaD is optimized to detect this signal, making a further crucial test of the standard paradigm and constraining the neutrino mass. Inflationary gravitational waves (IGW) would generate a B-mode signal at lower l, where QUaD begins to lose sensitivity, but where BICEP is optimized to probe for this potentially very important signature of fundamental physics. The ultimate sensitivity to IGW that can be reached will depend on the extent to which the lensing signal can be removed - QUaD will demonstrate the feasibility of this proposed technique. With respect of the broader impact, the enterprise of modern cosmology is one with which almost everybody can identify. The idea that through science humans can understand the origin, nature and fate of our Universe is fascinating, and frequently featured in newspapers and general magazines. QUaD collaborators work hard to communicate this excitement by interacting with the public in both formal and informal settings. Outreach and education related to the project will be disseminated through established structures and mechanisms such as those implemented by the Center for Cosmological Physics (CfCP) at U. Chicago. These programs, which reach out to local and distant K-12 school teachers and students, will use the excitement of exploring our universe to help attract women and minorities to science. Graduate and undergraduate education and research will be integrated in the construction of the instrumentation as well as in the analysis of the data. Students will play a major role in the project, exposing them to all aspects of scientific and engineering research. They will learn valuable skills, which will aid them in pursuing their careers, whether in industry or academia.