The Cosmic Ray Energy Spectrum Observed with the Surface Detector of the Telescope Array Experiment

TL;DR

The paper reports the measurement of the ultra-high energy cosmic ray spectrum using the Telescope Array's surface detector, revealing features like a dip and a cutoff consistent with theoretical predictions, through a novel simulation technique.

Contribution

It introduces a new simulation method for accurate acceptance calculation in ultra-high energy cosmic ray analysis using the TA surface detector.

Findings

Detection of a dip at 4.6 x 10^18 eV

Observation of a steepening at 5.4 x 10^19 eV

Results consistent with the GZK cutoff

Abstract

The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays with primary energies above 1.6 x 10^(18) eV. This measurement is based upon four years of observation by the surface detector component of TA. The spectrum shows a dip at an energy of 4.6 x 10^(18) eV and a steepening at 5.4 x 10^(19) eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of ultra-high energy cosmic ray surface detector data, that involves generating a complete simulation of ultra-high energy cosmic rays striking the TA surface detector. The procedure starts with shower simulations using the CORSIKA Monte Carlo program where we have solved the problems caused by use of the "thinning" approximation. This simulation method allows us to make an accurate calculation of the acceptance of the detector for the energies concerned.