The UMC Extensive Air Shower Array: Results and Prospects

The Utah-Michigan-Chicago array addresses the need for greater measurement sensitivity in searches for ultra-high energy gamma rays. Results from the Utah-Michigan experiment demonstrate the power of muon rejection. Even if photons inter-act in unconventional ways, the combination of CASA and the large muon array will measure these ffects. There have been many attempts to observe UHE (> 1014eV) gamma rays from celestial sources ince the reported observation ofCyg X-3 by the Kiel group in 19831. However, results so far have been inconclusive with most positive reports having weak statistical significance 2. Those experiments which have attempted to distinguish gamma-ray induced showers from the plentiful hadronic cosmic ray background have reported the surprising observation that the gamma showers have a muon content similar to ordinary cosmic rays. The Utah-Michigan-Chicago (UMC) Air Shower Array is designed to provide a definitive answer to the question of whether UHE sources exist. The techniqu