Probing the mystery of the highest energy cosmic particles with a large distributed observatory

Summary form only given. Scientists from 16 countries are building the largest ever Observatory for the Highest Energy Cosmic Particles. In the Argentina pampas, 1,600 water Cherenkov detectors will cover an area of 3,000 square kilometers overlooked by four fluorescence telescopes. The Cherenkov detectors are placed in a 1.5-kilometer triangular grid, powered by solar panels, timed by GPS's, and communicating via radio antennas. At the highest energies, one cosmic ray particle generates a shower that triggers dozens of detectors within microseconds as the shower reaches the ground. In dark moonless nights, the fluorescence telescopes observe the same showers through the ultraviolet emission of nitrogen molecules in the air excited by shower particles. The fluorescence telescopes are sensitive to the faint UV emission from tens of miles away. Together, the fluorescence telescopes and ground Cherenkov detectors form the most powerful observatory to ever study the highest energy cosmic ray showers. The goal of the Pierre Auger Observatory is to unveil the mysterious origin of particles with energies a billion times larger than present terrestrial accelerators can reach. During deployment, the Observatory has already produced intriguing results during construction. We will discuss the astrophysical and physical challenges of unveiling this high-energy mystery.