Results from the HiRes Experiment

The High Resolution Fly’s Eye (HiRes) Experiment has been in operation in monocular mode since 1997 and in stereo mode since late 1999. The published HiRes monocular spectrum is consistent with the GZK Suppression at 10 eV and observes an ankle structure at 10 eV. The preliminary stereo spectrum is consistent with the monocular spectrum. Various anisotropy studies with both monocular and stereo data have yielded null results. However, a possible correlation between HiRes stereo events taken before Jan., 2004 and BL-Lac objects has been reported, but remains to be verified or refuted by the analysis of the Hires data taken after Feb., 2004. Composition studies of Hires stereo data shows a predominantly light composition in the energy range 1018.0−1019.3 eV. We also report on the result of the proton-air cross section measurement from the tails of the XMAX distribution.