Solving the Mystery of the Ultra-High Energy Cosmic Rays The Pierre Auger Observatory Pablo Bauleo Physics Department Colorado State University Fort Collins CO Southern Site: Malargue, Argentina Northern Site: Southeast Colorado, USA

Historical high points 1912 Victor Hess discovers “penetrating radiation” from space 1938 Pierre Auger discovers Extensive air showers D Auger varied distance and lead covering Fast electronic counters Pb

For energy > 5 * Greisen, Zatsepin-Kuzmin (GZK) Cut Off Particles > 5 * eV must be < ~ few*50 Mpc away 1962: Penzias-Wilson: Cosmic Microwave Background p +  CMB  p +  0  n +  +

Energy (eV) Flux (m 2 sr s eV) -1 Highest energy event: 3.2 x eV Fly’s Eye in Utah in 1991 Today a lot is known about the cosmic ray flux… The Auger project is focused on the highest energies.

At the high end of the spectrum the energies are macroscopic Highest energy events are around 2*10 20 eV  30 Joules …dropping my laptop computer from shoulder height This energy is concentrated in, say, one proton. It corresponds to kinetic energy of… …a tennis ball at 40 miles per hour …a person walking slowly, deep in thought eV  1 CR/(km 2 sr century)

Cosmic Mysteries Where do Ultra High Energy Cosmic Rays Come From? No convincing acceleration process for explaining particle energy > eV A handful of super-GZK events have been reported. Sources of particles > eV must be closer than about 50 Mpc because of CMB No likely acceleration sites have been found nearby. The highest energy cosmic rays should point back to possible sources Point sources or uniform on the sky?

The primary cosmic ray initiates a shower. There are two basic detection techniques: (1) Particles reach ground (2) Nitrogen fluorescence 10% duty factor – dark nights Up to order particles Height ~20 km.a.s.l Height ~ 1500 m.a.s.l

Extracting information from an EAS Tank timing  Arrival direction Number of particles in tanks  Total Energy Telescope image (digital camera like)  Arrival direction Light detected  Total Energy Redundant measurement for cross-checks Animation of an event measured in Argentina

The Auger Collaboration 18 Participating Countries - 50 Institutions, >280 Scientists ArgentinaMexico Australia Netherlands Bolivia * Poland Brazil Slovenia Czech RepublicSpain FranceSouth Korea Germany United Kingdom Greece USA Italy Vietnam * Participating US institutions: UCLAMichigan Tech Case WesternMinnesota ChicagoNebraska ColoradoNew Mexico Colorado StateNortheastern Fermilab (and ANL)Penn State Louisiana StateUtah

Auger north is planned in Colorado Malargue is a small town on the high plains not far from a ski area in the Andes. Auger south is here.

View of Los Leones Fluorescence Site

Six Telescopes viewing 30°x30° each

Schmidt corrector ring  2.2 m opt. Filter (MUG-6) UV optical filter (also: provide protection from outside dust) Camera with 440 PMTs (Photonis XP 3062) Schmidt Telescope using 11 m 2 mirrors

Atmospheric Monitoring Balloon probes  (T,p)-profiles LIDAR at each FD building Central laser facility (fiber linked to tank)  light attenuation length  Aerosol concentration steerable LIDAR facilities located at each FD eye LIDAR at each eye LIDAR at each eye cloud monitors at each eye cloud monitors at each eye central laser facility central laser facility regular balloon flights regular balloon flights

Aligned Water Tanks as seen from Los Leones

Water Tank in the Pampa Solar Panel Electronics enclosure 40 MHz FADC, local triggers, 10 Watts Communication antenna GPS antenna Battery box Plastic tank with 12 tons of water three 9” PMTs

receiving ~20 tanks/week Tank Preparation and Assembly Transportation into field Water deployment installation of electronics Installation Chain

Central campus with visitors center Assembly building, yard

Coihueco (fully operational) Loma Amarilla (in preparation) Los Leones (fully operational) Los Morados (fully operational)

Proposed Layout in Southeast Colorado