Ultra High Energy Cosmic Rays in the North Some Results from the High Resolution Fly’s Eye

The High Resolution Fly’s Eye (HiRes) observatory collected Ultra High Energy Cosmic Ray (UHECR) data between 5/1997 and 4/2006. The experiment observed cosmic ray air showers via the air fluorescence technique and consisted of two observatory sites separated by 12.6 km in the western Utah desert. The two stations each measured the cosmic ray showers in monocular mode, however, the data from the two stations can also be combined to form a stereo measurement of the air showers. The experiment measures such properties as the energy spectrum, chemical composition, and p‐air cross‐section of these cosmic rays. It also searches for point sources and other anisotropy. The spectrum is measured above ∼3 × 10¹⁷ eV and shows significant structure including the “ankle” and a steep fall off which is consistent with the expectation of the GZK threshold. The spectrum is inconsistent with a continuing spectrum at the 5σ level. The composition is measured using the X_max technique. It was found to be predominantly light and unchanging above 10¹⁸ eV. Finally, several different styles of searches for anisotropy in the data were performed. There are tantalizing hints including potential correlation with BL Lac objects and the “AGASA triplet”, however these will need to be confirmed with an independent data set. Many members from HiRes have now joined a contingent from the old AGASA collaboration and the new group — The Telescope Array (TA) Project — will merge the techniques of its two predecessors. TA data collection begins mid‐2007.