Air Fluorescence Calorimetry with the High Resolution Fly’s Eye and Telescope Array Experiments

The air fluorescence technique was first successfully deployed on the Fly’s Eye Experiment (1981–1993) by the University of Utah. Its successor, the High Resolution Fly’s Eye (HiRes) experiment has further exploited this technique, first in hybrid mode with the MIA muon array (1993–1996), and then in monocular and stereoscopic modes (1997–2006). Results from HiRes will be presented, including evidence for the Greisen‐Zatsepin‐K’uzmin (GZK) Effect predicted 40 years ago. Most recently, members of the HiRes are collaborating with groups from Japan, led by University of Tokyo, to construct and operate the Telescope Array (TA) experiment, which will deploy a large scintillation‐based ground array in combination with fluorescence detectors. Funding for TA in the US has already been approved by NSF. TA will begin operation in 2007.