HiRes and TA spectrum measurements

Dept. of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA

^a e-mail: bergman@physics.utah.edu

Abstract

The High Resolution Fly's Eye and Telescope Array experiment are separate experiments, although there is significant overlap in both equipment and personnel. Despite using different measurement techniques the two experiments provide nearly identical measurements of the UHECR cosmic ray spectrum, with agreement in overall flux level and the positions of the spectral features of the Ankle and the GZK Cutoff. This similarity arises despite using entirely different detector techniques. What unites the measurements from the two experiments is the experimental methodology of a thoroughgoing use of Monte Carlo detector simulations which are required to produce distributions of observables which are the same as those in the actual data. The detector simulation is then used to estimate exposures and acceptances which are not directly measurable. The procedure of verification through data/MC comparisons removes many of the systematic errors associate with model assumptions inherent in the MC simulation.