Research Highlight
February 12, 2008
CAPMAP Announces Final Results: CMB Polarization at Small Angular Scales
by Bruce Winstein, Colin Bischoff, and Jeff McMahon
CAPMAP Announces Final Results: CMB Polarization at Small Angular Scales
The Cosmic Anisotropy Polarization MAPper (CAPMAP) collaboration has announced new measurements of the cosmic microwave background polarization, extending the range of previous measurements to smaller angular scales.

The polarization of the cosmic microwave background (CMB) provides a unique window into the physics of the early Universe. Polarization can be decomposed into two components: the dominant E-modes and the much smaller B-modes. E-modes are sourced by the same density perturbations that give rise to the observed temperature anisotropies in the CMB while B-modes arise from both gravity waves generated during the period of inflation and gravitational lensing of the CMB by the cosmic web of dark matter.

Using the 7-meter Crawford Hill Antenna in New Jersey, CAPMAP completed its final data-taking season in the winter of 2004-2005, collecting over 900 hours of good data.
The detected E-mode spectrum has a significance level of 11 sigma, and is in good agreement with the predictions of the concordance ΛCDM model.

Figure: Compilation of measurements of the CMB E-mode power spectrum, with results from both CAPMAP pipelines.
The B-modes will be the signature of ''new physics'' and the CAPMAP data are currently the most sensitive at the finest angular scales: the figure is a compilation of 95% confidence level upper limits on B-mode power. CAPMAP had two independent and complementary analysis pipelines, observed at 2 frequencies, used a novel scan strategy and data selection criteria, and limited a large number of possible effects which could corrupt the data.
CAPMAP, which took data initially in 2003, is one of KICP's inaugural projects. A new collaboration with Princeton began after Bruce Winstein returned from a sabbatical year there, working with Suzanne Staggs and her group. The University of Miami and NASA's Jet Propulsion Laboratory later joined the collaboration. The CAPMAP team at Chicago includes current and former KICP fellows Matt Hedman, Jeff McMahon, and Dorothea Samtleben; graduate students Colin Bischoff, Kendrick Smith and Keith Vanderlinde; and undergraduates Liam Fitzpatrick, Peter Hamlington, Hannah Barker and Maire Daly.
in the circle at top left: Matthew Hedman
back row (L-R): Jeff McMahon, Lewis Hyatt, Keith Vanderlinde, Colin Bischoff, Bruce Winstein
middle row (L-R): Suzanne Staggs, Phil Farese, Dorothea Samtleben
front row (L-R): Josh Gunderson, Denis Barkats.
The study of CMB polarization is one of the key goals of the KICP. The DASI experiment was the first to detect CMB polarization. In total it operated at the South Pole for 3 years. CAPMAP obtained an even more significant detection with a comparable number of detectors and just a few months of data. A difference in scan strategy was one of the reasons for this, as well as using the 7m Crawford Hill telescope that gave better sensitivity at the angular scales where the polarization signal peaks. QUaD will provide even better detections - it has operated at the South Pole for 3 years with more detectors, each with greater sensitivity. This is all good news for future KICP projects. The CAPMAP group is moving on to QUIET, which uses the same style of detectors, now packaged (by JPL) in a small ''polarimeter on a chip;'' QUIET will deploy to the Atacama desert in Chile in May. And in a few years the SPT group will be turning its attention to polarization.

The CAPMAP 2008 paper: New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz, CAPMAP Collaboration: C. Bischoff, L. Hyatt, J. J. McMahon, G. W. Nixon, D. Samtleben, K. M. Smith, K. Vanderlinde, D. Barkats, P. Farese, T. Gaier, J. O. Gundersen, M. M. Hedman, S. T. Staggs, B. Winstein
Related Links:
KICP Members: Jeff McMahon; Bruce D. Winstein
KICP Students: Colin Bischoff
Scientific projects: CAPMAP