Study of the Highest Energy Cosmic Rays with the Pierre Auger Observatory

Colorado School Of Mines, Golden CO

Investigators

Abstract

The current measurements of energy spectra, anisotropy, particle composition, and proton-air cross section demonstrate that the Pierre Auger Observatory has an unprecedented view of the high-energy Universe and access to particle physics at energies beyond the LHC. With Auger now operating in its full configuration of Surface Detector (SD) stations and air Fluorescence Detectors (FD), the data collected thus far presents interesting puzzles and exciting opportunities. The suppression of the energy spectrum above 60 EeV implies a Greisen-Zatsepin-Kuzmin (GZK) or GZK-like effect that screens the isotropic distant Universe. Events above 55 EeV show hints of extra-galactic anisotropy within this horizon. FD elongation rate measurements currently extend only to 30 EeV but suggest either a transition from lighter to heavier primaries, or a glimpse of new physics beyond LHC energies. These measurements have strong implications about the nature of the highest energy sources. This award will support this group in leading the effort to complete an upgrade to the suite of atmospheric laser test beam systems at the Observatory. Pulsed lasers probe Auger's enormous dynamic atmospheric calorimeter and generate air shower-like tracks in the FDs. Planned applications include monitoring the end-to-end absolute photometric calibration of the FD to better than 5%, a necessary step to reduce the uncertainty on the energy scale. This has implication in the determination of the volume up to the GZK horizon. Other applications include an independent precision measurement of the largest time-varying calibration term (aerosol optical depth) via Raman LIDAR. This group will also extend methods that they have developed to search for exotic particles. A technique to measure the speed of extensive air showers has been benchmarked against laser shots and then applied to stereo and hybrid events. The technique is sensitive to massive exotic objects traveling at a fraction of the speed of light that are able to generate an optical signature in the FD. Among the Broader Impacts planned under this award is the development of a relationship with an area high school for at-risk youth. The group envisions a program of physics demonstrations that make use of material developed for the Mines modern physics courses, including a cloud chamber and coincident particle detectors. The role of aerosols in climate forcing is not well understood. There are relatively few aerosol profile measurements in the southern hemisphere. Raman LIDAR is a standard technique that will both enhance the usefulness of the Auger atmospheric data and enable more direct comparisons with data in the atmospheric science community.