Telescope Array Hybrid Composition and Auger-TA Composition Comparison

TL;DR

This paper presents an analysis of nine years of Telescope Array data measuring atmospheric depth of air shower maximum ($X_{ extrm{max}}$) to infer the composition of ultra high energy cosmic rays, comparing results with Auger.

Contribution

It introduces a detailed $X_{ extrm{max}}$ analysis method combining surface and fluorescence detectors and compares composition results with Auger data.

Findings

Data favor certain primary particle compositions at high energies.

Comparison shows similarities and differences between TA and Auger results.

Analysis constrains models of UHECR sources and propagation.

Abstract

Telescope Array (TA) has completed analysis of nearly nine years of data measuring the atmospheric depth of air shower maximum ($X_{\textrm{max}}$) utilizing the TA surface detector array and the Black Rock Mesa and Long Ridge fluorescence detector stations. By using both the surface array and the fluorescence detector, the geometry and arrival time of air showers can be measured very precisely providing good resolution in determining $X_{\textrm{max}}$. $X_{\textrm{max}}$ is directly related to the air shower primary particle mass and is therefore important for understanding the composition of ultra high energy cosmic rays (UHECRs). UHECR composition will help answer questions such as the distance and location of their sources. We discuss the experimental apparatus, analysis method, and $X_{\textrm{max}}$ data collected. We compare the energy dependent distributions of the observed data to detailed Monte Carlo simulations of four chemical species, then test which individual species are not compatible with the data through an analysis of the shapes of the distributions. We also discuss the present state of composition analysis and interpretation between the Auger and TA experiments. These are the two largest UHECR observatories in the world with large exposures and should shed light on UHECR composition.