The Pierre Auger Observatory (PAO) is a large International endeavor aimed at the study of Ultra?High Energy Cosmic Rays (UHECRs). PAO is a hybrid experiment with a large array of surface detectors measuring the footprint of an extensive air shower when it reaches the Earth and with multiple fluorescence telescopes measuring the shower in the space above. They have started deploying a low energy extension to study the galactic to extra?galactic transition. The latest PAO results have confirmed the long anticipated GZK suppression in the spectrum due to interactions with the microwave background. However, the sources of the highest energy particles and questions about how they are accelerated in the first place are among the most important topics in particle astrophysics today. One suspected source is Active Galactic Nuclei, which are among the most energetic objects known in the Universe.
This award will fund the continued participation of this investigator in the areas of detector calibration, maintenance and operation, and analysis of PAO data. His group employs undergraduate students in detector construction, operation, atmospheric monitoring, data analysis and software development. The group participates in the well?established PAO outreach program in Argentina with activities including the preparation of materials and presentations at the Visitor?s Center, public talks, visits to schools, science fairs, and courses for teachers and students.
Cosmic rays are fast-moving particles from space that constantly bombard the Earth from all directions. Most of the particles are either the nuclei of atoms or electrons. Of the nuclei, most are single protons -the nuclei of hydrogen atoms- but a few are much heavier, ranging up to the nuclei of lead atoms. Cosmic ray particles travel at nearly the speed of light, which means they have very high energy. Some of them, in fact, are the most energetic of any particles ever observed in nature. The highest-energy cosmic rays have a hundred million times more energy than the particles produced in the Large Hadron Collider, the world's most powerful particle accelerator. To learn about the nature of these highest energy cosmic rays, we measure their energy and their direction as they arrive from space. Cosmic rays of modest energy can be measured directly by sending detectors to heights above the Earth's atmosphere. For example, using balloons and satellites. For high energy cosmic rays, however, it is more efficient to study the interactions between these particles and the Earth's atmosphere. An air shower occurs when a fast-moving cosmic ray particle strikes an air molecule high in the atmosphere, creating a violent collision. Fragments fly out from this collision and collide with more air molecules, in a cascade that continues until the energy of the original particle is spread among millions of particles raining down upon the earth. We thus detect each cosmic ray indirectly by observing the shower of particles it produces in the air. By studying the air showers, we are measuring the properties of the original cosmic ray particles. Using the Pierre Auger Cosmic Ray Observatory we are studying ultra-high energy cosmic rays, the most energetic and rarest of particles in the universe. While much progress has been made in nearly a century of research in understanding cosmic rays with low to moderate energies, those with extremely high energies remain mysterious. The Auger Project was first proposed in 1992 by Jim Cronin and Alan Watson. The Southern Auger Observatory, located near Malargüe, Argentina, a town in Mendoza Province that lies just east of the Andes Mountains, has been collecting data since early 2004. The participating countries shared the $54 million construction budget, each providing a minor fraction of the total cost. Construction was completed in 2008. Today, nearly 500 physicists from more than 90 institutions in 19 countries around the world are collaborating to operate the Observatory. The Pierre Auger Observatory is a large grid of detectors. The Southern array covers 3,000 square kilometers and has detectors spaced 1.5 km apart in a triangular pattern. Using these detectors, we can measure air showers with the goal of tracking high-energy cosmic rays to their unknown sources. For nearly a century, cosmic ray research has solved important scientific problems, and uncovered new ones. In that tradition, the Pierre Auger Collaboration works to answer the questions of the highest-energy cosmic rays, one of the great scientific mysteries of our time. You can browse ultra high energy cosmic rays detected with the Pierre Auger Observatory at our Public Event Display: http:/auger.colostate.edu/ED/
