The Pierre Auger Observatory (PAO) is an international project aimed at the study of the highest energy cosmic rays. These highest energy particles in the Universe are very rare, and the elucidation of the mystery of their origin is one of the key challenges in modern astrophysics. They interact with the cosmic microwave background, as noted in 1966 by Greisen, Zatzepin and Kuz'min. As a result, cosmic rays with energies of ~10**20 eV are strongly attenuated over cosmological distances, and sources nearer than ~50 Mpc are expected to be dominant. The PAO, a large hybrid detector employing both the surface detector and air fluorescence techniques, is nearing completion in Argentina.
The Ohio State group has played a key role in the design, integration, commissioning, and management of the surface detector electronics chain and has played a leading role in the development of the detector trigger and the automated detector calibration scheme. Their analysis efforts benefit from their detailed understanding of the design and operation of the surface detector and they plan to continue their activities in support of detector operation and maintenance, and participation in the analysis of the Auger data.
The group has been active in engaging the public and providing opportunities for understanding the fascinating science involved in cosmic rays, by conducting tours of facilities both in the U.S. and in Argentina for schoolchildren and others. They are engaged in a program of education and outreach through a partnership with a local high school, where they are introducing students to cosmic ray research.
Cosmic rays are subatomic particles with very high energies which constantly bombard the Earth from space. Some cosmic rays have incredibly high energies, up to tens of Joules; this is the typical energy carried by a tennis ball in play, but all of this energy is carried by a single subatomic particle. The highest energy cosmic rays are extremely rare, and impact us at a rate of one particle per square kilometer per century. How this much energy is transferred to a single particle is a mystery. To detect these cosmic rays, a large detector is required. We have built the Pierre Auger Observatory in western Argentina. Auger uses the Earth's atmosphere as our detector, transforming the cosmic rays into a shower of lower energy particles which can be detected as a flash of light in the atmosphere by 24 specialized fast telescope cameras, and using 1600 water tanks on the ground to detect the Cherenkov light emitted by particles which reach the Earth's surface and pass through the tanks. These detectors are spead over 3000 square kilometers, about the area of the state of Rhode Island. The water tank instrumentation is solar powered and communicates with a central monitoring station using specialized cellular-like communications technology. The entire observatory is syncronized to ten billionths of a second using the GPS system. Using this data, we can infer the energy and direction of each arriving high energy cosmic ray, and derive clues about the nature of the original subatomic particle. Auger has been constructed by a collaboration among over 300 scientists in 19 countries, and we are now in a stable data taking mode. Our work under this particular grant involves three main thrusts. First, since the PI played a leadeship role in the development of the electronics for the surface detector we continue to provide support for the onsite staff who now maintain this system, and as members of the colloaboration we take shifts operating parts of the detector. Second, we have worked to understand the effects of the Galactic magnetic field on changing the arrival directions of the cosmic rays, and studied what this can tell us about where they are made and what kind of subatomic particle they are. We have also studied the penetration of showers into the atmosphere, which tells us both about the nature of the subatomic particle and of its first interaction with Earth's atmosphere. This work is challenging because we must disentangle several simultaneous effects, differing in subtle ways, with limited information. It is particularly interesting because the center-of-mass energies we are able to study are more than ten times greater than the highest energies we can create in the most powerful manmade accelerators. This work has resultied in publications in peer-reviewed journals, presentations at international conferences, and Ph.D. theses. The primary broader impact of our work is the development of STEM human resources, both in the short and long term. Our students and postdocs become proficient in using a wide variety of experimental apparatus and data analysis tools. They go on to positions in universities, government labs, and private industry, often applying the skills gained in basic research to applied problems which impact our economic well being and our nation's defense. We also share our work with undergraduates and with K-12 students to inspire the next generation of scientists and engineers.
