GEOGRAPHIC LOCATION OF THE PIERRE AUGER OBSERVATORY Northern Hemisphere: Millard County, Utah Southern Hemisphere: Malargüe Mendoza Province Argentina Malargüe

The Engineering Array Locations of the first 40 surface detector tanks The first 40 surface detectors Malargüe, Argentina

Cosmic rays are particles which travel through outer space and constantly bombard the Earth from all directions. The highest-energy cosmic rays are millions of times more energetic than particles produced in the world’s largest particle accelerators. The origin of ultra-high energy cosmic rays is unknown. High-energy cosmic rays may be indirectly detected at the surface of the Earth by observing showers of particles they produce in the atmosphere. The Pierre Auger Observatory will detect and study these air showers in order to resolve the mysteries of ultra-high energy cosmic rays: their nature and their origin. A possible origin of ultra-high energy cosmic rays: collisions of two galaxies Scientific Aspects of the Pierre Auger Observatory The Search for the Origin of Ultra-High Energy Cosmic Rays

The International Collaboration of the Pierre Auger Observatory About 250 scientists from more than 30 institutions and 19 countries participate in the experiment. Participating Countries: Argentina, Armenia, Australia, Bolivia, Brazil, China, Czech Republic, France, Germany, Greece, Italy, Japan, Mexico, Poland, Russia, Slovenia, United Kingdom, United States, Vietnam Collaborating Institutions in the United States: University of California at Los Angeles University of Chicago Colorado State University University of Colorado The Fermi National Accelerator Laboratory Louisiana State University Michigan Technological University University of Mississippi University of Nebraska University of New Mexico Northeastern University Pennsylvania State University University of Utah Participating countries shown in red.

The project is named after the eminent French physicist, Pierre Auger, who discovered cosmic ray air showers in Directors of the Pierre Auger Observatory James Cronin (University of Chicago, USA) Alan Watson (University de Leeds, United Kingdom) The Pierre Auger Cosmic Ray Observatory

The development of a cosmic ray air shower in the atmosphere

The Detectors The Observatory employs 1600 particle detectors uniformly spaced over 3000 square kilometers to measure cosmic ray air showers. Also on dark nights, sensitive light detectors observe the faint fluorescence created by collisions between air shower particles and other air molecules. Surface detector Fluorescence telescope

Surface Detectors Antenna for transmitting data Solar panel for charging battery Tank containing liters of pure water Light detectors Electronic apparatus and battery

Two types of detectors work together to measure cosmic ray air showers Surface detectors Fluorescence telescope Angle Air shower plane 1.5 kilometers Primary cosmic ray

Members of the collaboration with the first Surface Detector tank installed in the field Solar panel

An “air shower” of secondary particles is created by collisions with air molecules A primary cosmic ray (usually a proton or light nucleus) impinges on the earth’s atmosphere from outer space A grid of particle detectors intercepts and samples a portion of the arriving secondary particles The number of secondaries is related to the primary cosmic ray’s energy The relative arrival time of secondaries tells the incident direction of the primary cosmic ray How is a cosmic ray air shower formed and detected?

Cosmic ray air showers were first observed by one of the fluorescence detectors in May 2001! Computer-reconstructed image: cosmic ray trail in atmosphere “seen” by multi-channel fluorescence camera