This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). It will provide funds to work on the Pierre Auger Observatory in Malargue, Argentina. The Observatory is the world's largest detector for "ultra-high energy" cosmic rays. The data promises to shed light on the origin of these cosmic rays, the highest energy particles of the (known) Universe. The measured energy spectrum of cosmic rays extends up to eleven orders of magnitude greater than the equivalent rest mass of the proton. No single source or source class is expected to be responsible for the flux over such a wide range of energies. The large energies of these particles imply that they are accelerated in violent processes in extreme astrophysical objects, for example Active Galactic Nuclei, which contain supermassive black holes, or Gamma Ray Bursts. With its major involvement in IceCube and in neutrino physics and phenomenology, UW-Madison is a natural place to explore the possibilities of the Pierre Auger Observatory as a neutrino detector, and to further study the connection between cosmic rays and neutrinos.
The PI's areas of particular strength and interest are the search for discrete sources and anisotropies in the cosmic ray arrival direction distribution and the search for neutrinos at ultra-high energies. His second main effort will be the study of the atmosphere and its influence on cosmic ray measurements. The energy calibration of the detector relies on the air fluorescence detector and requires corrections for atmospheric absorption and scattering to be applied.
The broader impact of the program includes outreach activities aimed at enhancing the public's understanding of science, for example through brochures like "Cosmic Extremes" and involving K-12 teachers and high school students in ongoing research.