Results from the High Resolution Fly’s Eye Experiment

The High Resolution Fly’s Eye Experiment (HiRes) is a collaboration of seven institutions from the U.S. and Australia. HiRes consists of two fluorescence detector sites, HiRes-1 and HiRes-2. It is designed to study the spectrum, composition, and anisotropy of ultra-high energy cosmic rays (UHECR) using stereo-scopic reconstruction of shower geometries. The HiRes-1 site has been in operation since June, 1997. Over 1000 hours of good weather monocular data has been analyzed. A preliminary energy spectrum is presented based on this monocular data set and compared to the original Fly’s Eye results. The HiRes-2 detector is nearly complete as of August, 1999 and had begun limited data-taking with a partial detector in April, 1999. Some high energy stereo events have already been observed.