This is a proposal to continue the participation of the University of Chicago (UC) in the Pierre Auger Observatory (PAO). The observatory is designed to study the origin and nature of cosmic rays with energies greater than 10^19 eV by measuring their energy, their composition, and the distribution of arrival directions over the entire sky with large statistics and careful control of systematic effects. The Southern PAO, under construction in Argentina, is the first hybrid detector that combines the two best-developed techniques of measuring showers caused by ultra-high energy cosmic rays (UHECR). The observatory detects shower particles that reach the surface with a surface array and the longitudinal development of the shower through the fluorescence produced in the atmosphere. This combination is essential for accurate energy measurements and reliable composition studies.
This proposal represents the merging of two NSF-supported groups at UC. Cronin has been instrumental in the formation of the international collaboration of the 15 countries now building the observatory. Olinto has focused on the theoretical aspects of the origin of these highest energy particles as well as the strengths and limitations of the air shower techniques. The integration of the two groups into a single effort will benefit both the research goals and the training of students by involving them in all aspects of science: from the construction and operation of the PAO to the analysis and interpretation of its data.
Broad Impact: The discovery of the origin of the highest energy particles will impact both astrophysics and particle physics. The fundamental questions involved in the study of UHECR have drawn the attention of a large scientific community eagerly awaiting the results. The Southern PAO has had a major impact on public education and outreach throughout the participating countries across the globe: from Argentina to Vietnam. In collaboration with the Adler Planetarium/UC effort in astrophysics visualization, this proposal enlarges the public reach and strengthens the depth of physics and astrophysics content of the education and public outreach effort by developing 3D and 2D visualizations of the highest energy showers, their detection methods, and possible cosmic origins.
