ENERGY SPECTRUM MEASURED BY THE TELESCOPE ARRAY SURFACE DETECTOR

Abstract

OF THE DISSERTATION Energy Spectrum Measured by the Telescope Array Surface Detector by Dmitri Ivanov Dissertation Director: Professor Amitabh Lath Two conflicting measurements of the ultra high energy cosmic ray (UHECR) flux have been reported by the Akeno Giant Air Shower Array (AGASA) and the High Resolution Fly’s Eye (HiRes) experiments. HiRes observes a ∼5σ suppression at E = 10 eV, which is in agreement with the prediction of Greisen-ZatsepinKuz’min (GZK) theory. AGASA, in contrast, sees the flux extended well beyond E = 10 eV with no visible break, suggesting that the flux is limited only by the rate at which the sources can produce the UHECR and not by interaction of energetic particles with the cosmic microwave background, thus challenging the relativistic invariance principle. In response to this discrepancy, a new experiment named the Telescope Array (TA) has been deployed, which combines the detection elements used separately by HiRes and AGASA. We describe the TA surface detector (SD) analysis using a technique new to the field, which consists of a detailed Monte-Carlo (MC) simulation of the SD response to the natural cosmic rays, validating the MC by comparing its distributions with the data, and calculation of the SD aperture from the MC.