High Energy and Nuclear Physics

The DOE Office of High Energy and Nuclear Physics sponsors major experimental facilities and theoretical studies, as well as computational simulations and analyses of experimental data.

In 2002 the MAXIMA data analysis team documented their successful approach to recovering a map of the cosmic microwave background (CMB); their methods will be applicable to other CMB experiments. Accomplishments in nuclear physics included the only quantum Monte Carlo calculations of 6- through 10-nucleon systems that use realistic interactions and are accurate to 1–2% for the binding energies

Research in lattice quantum chromodynamics (QCD) included the first simulations to explore the finite temperature phase diagram with an improved staggered fermion action; a study of chiral properties of pseudoscalar mesons with overlap fermions; and simulations of lattice QCD at finite isospin density..

Making Maps of the Cosmic Microwave Background

The cosmic microwave background (CMB), a “snapshot” of the Universe as it was only 300,000 years after the Big Bang, provides the most powerful discriminant between different cosmological models. To date, CMB datasets have ruled out an entire class of models (based on topological defects) for the generation of primordial density perturbations in the Universe; have demonstrated the spatial flatness of the Universe as a whole; and, coupled with supernova data, have given a first measurement of the overall mass-energy budget for the Universe.

	Figure 1   Pixel domain correlations of the noise projected on the sky. All three panels show a level of the correlations relative to the rms value of the noise for the same pixel, which is marked with an x. This pixel was observed twice during the MAXIMA-I flight. The noise correlations for the first observation are shown in the left panel, and these for the second one in the middle panel. The right panel shows the final co-added noise correlations. Due to the MAXIMA-I scanning strategy and the presence of the noise correlations in the time domain, the noise correlation pattern in pixel domain is highly anisotropic and strongly correlated as a result of any single observation of a pixel. However, the combined noise for all pixels that were observed twice is significantly less correlated and more isotropic. (Click on image for larger version.)

There is much more information still to be mined from CMB data, especially from current and future satellite missions (MAP and Planck), but the size of the datasets presents new challenges for timely and precise data analysis. Stompor et al. have documented how those challenges were met successfully in the analysis of data from the MAXIMA-I balloon-borne experiment, which required improvement of existing methods and tools as well as development and testing of new ones.

The MAXIMA collaborators present a comprehensive, consistent approach to recovering a map of the sky and estimating its error matrix in realistic circumstances. Their approach includes data preprocessing and noise estimation; a suite of different map-making methods that simultaneously produce both a map and a corresponding pixel-pixel noise correlation matrix (Figure 1); ways of handling systematic effects within the general framework of maximum likelihood map making; iterative algorithms for time-domain noise estimation; and numerical tests for checking the consistency of the analysis. Their methods are expected to be applicable to other current and future CMB experiments.

INVESTIGATORS
J. D. Borrill and G. F. Smoot, Lawrence Berkeley National Laboratory and University of California, Berkeley; R. Stompor, University of California, Berkeley and Copernicus Astronomical Center, Warsaw; A. H. Jaffe, A. T. Lee, S. Oh, B. Rabii, P. L. Richards, C. D. Winant, and J. H. P. Wu, University of California, Berkeley; A. Balbi, Università Tor Vergata, Rome; P. G. Ferreira, University of Oxford; S. Hanany, University of Minnesota.

PUBLICATION
R. Stompor, A. Balbi, J. D. Borrill, P. G. Ferreira, S. Hanany, A. H. Jaffe, A. T. Lee, S. Oh, B. Rabii, P. L. Richards, G. F. Smoot, C. D. Winant, and J. H. P. Wu, “Making maps of the cosmic microwave background: The MAXIMA example,” Phys. Rev. D 65, 022003 (2001).

URL
http://www.nersc.gov/~borrill/