The QUaD telescope in its ground shield

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The QUaD Experiment

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QUaD is funded by the National Science Foundation in the US, and in the UK by the Particle Physics and Astronomy Research Council

New results on astro-ph here
QUaD instrument described on astro-ph here
QUaD sets new standard in CMB Polarization Measurements

The QuaD experiment, situated at at the National Science Foundation's Admunsen-Scott South Pole Station, has made high precision measurements of the polarization of the Cosmic Microwave Background radiation. These measurements agree well with the predictions made by the "standard" cosmological model, in which the contents of the universe are dominated by dark matter that does only interacts with the normal matter through gravity, and dark energy, that is causing the universe to expand at an accelerating rate.
The Cosmic Microwave Background radiation was emitted when the universe was about 400,000 years old. Due to the subsequent expansion of the universe, the radiation is now most strongly visible at the microwave and millmeter (shorter microwave) wavelengths at which QUaD observes. Because these wavelengths are strongly absorbed by water vapor, QUaD is situated at the South Pole, where the atmosphere is very dry, allowing the faint cosmic signals to be detected. QUaD was operated from 2005 to 2007, and observed only during the Antarctic winter, when the sun remains below the horizon for six months, and the temperatures drop as low as -100 F (-70 C). The QUaD camera is shown opposite, and contains detectors that are sensitive to both the polarization and the intensity of the microwave background radiation.
The picture opposite show high resolution maps made by QUaD that distinguish between two types of polarization signal. The brighter signal on the left is called E-mode polarization, that on the right is called B-mode. The standard cosmological model predicts that the polarization should be dominated by the E-modes pattern which are free of the vortex-like patterns contained in the B-modes. The B-mode map from QUaD is consistent with random chance caused by noise in the instrument, while the E-mode signal is strongly detected.
The E-modes indicate the presence of clumps in the early universe that later cooled and under the force of gravity, collapsed together to become the stars and galaxies we see throughout the universe today. QUaD has verified that the statistical properties of the signal agree well with the predictions of the standard model. In particular the process of the gravitational collapse of the clumps while the universe is very hot sets up certain resonances (like musical tones) in the matter that causes the polarization patterns to be particularly strong for clumps of a particular size. These resonances can be seen in the picture opposite, which shows the polarization strength as a function of the angular size of the clump on the sky. The solid line shows the predictions of the standard cosmological model, and the points show the QUaD measurements.
QUaD's results have substantial implications for the future directions of research in cosmology. Polarization measurements of the Cosmic Microwave Background are the current best candidate to directly observe evidence for the inflationary model of the universe, in which scientists believe that the universe expanded at an enormously exponential rate shortly after the Big Bang. Furthermore, QUaD confirms to physicists that they must understand in full the strange natures of dark energy and dark matter if they are to unravel the cosmic puzzle set out in the past decade by cosmological observations.
QUaD is a collaboration led by the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University and the Stanford Linear Accelerator, the Kavli Institute for Cosmological Physics at the University of Chicago, the California Institute of Technology and Jet Propulsion Laboratory, Cardiff University (United Kingdom) and University of Edinburgh (United Kingdom). Funding in the US has been obtained from the National Science Foundation, and in the UK by the Particle Physics and Astronomy Research Council.

Last updated May 13th 2008
Copyright © Sarah Church, 1999-2008