Study of Ultra-High Energy Cosmic Ray Composition Using Telescope Array's Middle Drum Detector and Surface Array in Hybrid Mode

TL;DR

This study uses Telescope Array's hybrid detection to analyze ultra-high energy cosmic ray composition, finding a predominantly protonic composition consistent with other experiments and confirming the equivalence of stereo and hybrid detection methods.

Contribution

It introduces a new pattern recognition technique for composition analysis and demonstrates the consistency of hybrid and stereo detection methods in UHECR studies.

Findings

Data favor a light, protonic composition over iron.

Results align with Pierre Auger Observatory data.

Hybrid and stereo methods are equivalent in composition measurements.

Abstract

Previous measurements of the composition of Ultra-High Energy Cosmic Rays(UHECRs) made by the High Resolution Fly's Eye(HiRes) and Pierre Auger Observatory(PAO) are seemingly contradictory, but utilize different detection methods, as HiRes was a stereo detector and PAO is a hybrid detector. The five year Telescope Array(TA) Middle Drum hybrid composition measurement is similar in some, but not all, respects in methodology to PAO, and good agreement is evident between data and a light, largely protonic, composition when comparing the measurements to predictions obtained with the QGSJetII-03 and QGSJet-01c models. These models are also in agreement with previous HiRes stereo measurements, confirming the equivalence of the stereo and hybrid methods. The data is incompatible with a pure iron composition, for all models examined, over the available range of energies. The elongation rate and mean values of Xmax are in good agreement with Pierre Auger Observatory data. This analysis is presented using two methods: data cuts using simple geometrical variables and a new pattern recognition technique.