Ground-based detector in Mexico images highest-energy light

BBC : The High-Altitude Water Cherenkov (HAWC) Observatory , being built near Puebla, Mexico, is already detecting cosmic- and gamma-ray particles in Earth’s atmosphere. HAWC will consist of 300 tanks of pure water with detectors at the bottom. As the high-energy particles enter the atmosphere, they strike molecules in the air, setting off a chain-reaction particle cascade called an extensive air shower. When those faster-than-light particles enter HAWC’s water tanks, they emit the electromagnetic equivalent of a sonic boom. It is those flashes of light that can be used to determine the type, energy, and direction of the primary cosmic- and gamma-ray particles. With just 30 tanks up and running, HAWC is already producing images, according to HAWC collaboration member Thomas Weisgarber of the University of WisconsinâMadison during his presentation Saturday at the April meeting of the American Physical Society in Denver. The full array should be in place by 2014.