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

Abstract

The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays (UHECRs) with primary energies above 1.6 × 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 × 10 18 eV and a steepening at 5.4 × 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 UHECR surface detector data, that involves generating a complete simulation of UHECRs 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.

A Study on Anisotropy in the Arrival Directions of Ultra-High-Energy Cosmic Rays Observed by Pierre Auger Observatory

“…This would result in the suppression in the cosmic ray energy spectrum above the so called GZK cutoff E GZK ∼ 4 × 10 19 eV, if the sources are distributed over the whole universe. If this suppression is true, as indicated by recent observations [5][6][7], it implies that UHECR with energies above the GZK cutoff mostly come from relatively close extragalactic sources within the GZK radius r GZK ∼ 100 Mpc. One consequence of this would be anisotropy in the arrival directions of ultra-high-energy cosmic rays (UHECR), since the matter within the GZK radius is distributed inhomogeneously and the UHECR sources are more or less correlated with the matter distribution.…”

“Lomonosov” Satellite—Space Observatory to Study Extreme Phenomena in Space

“…For many years, the situation around the GZK cutoff was unclear and sometimes controversial until a predecessor of TA, the High Resolution Fly's Eye (HiRes) experiment, observed a suppression of the CR flux at ∼ 60 EeV with a statistical significance of over 5σ (Bergman and High Resolution Fly's Eye Collaboration 2007;Abbasi et al 2008). The remarkable discovery was soon confirmed by Auger (Abraham et al 2008b) and later by TA (Abu-Zayyad et al 2013b).…”

Neutrinos and the origin of the cosmic rays

“…The solid curves imply that neutron emission dominates the UHECR escape, the dashed curves mean that directly escaping protons dominate at the highest energies, where the Larmor radius reaches the width of the fireball shells. In the left panel, the observed UHECR data from the Telescope Array [20] are reproduced by the model (red curves) for two different parameter sets. Additionally, the fit range is gray-shaded, and the χ 2 /d.o.f.…”