33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013 THE ASTROPARTICLE PHYSICS CONFERENCE A Comparison between Hadronic Interaction Models and Observations by the Telescope Array

Abstract: The observation of ultra-high energy cosmic rays presents the opportunity to study particle interactions orders of magnitude more energetic than can be attained in particle colliders. However, the events are rare and only their extensive air showers can be studied experimentally. Monte Carlo shower simulation programs use interaction models which extrapolate cross sections from accelerator experiments and attempt to predict how experimental shower data should appear. The models make two sets of observable predictions. The first set predicts the longitudinal development of cosmic ray air showers, which can be tested by an air fluorescence detector. The second set of predictions pertain to the lateral distribution of secondary particles at the ground which can be measured by an array of particle detectors. Comprehensive comparisons will be shown between showers observed by the Telescope Array and simulated showers utilizing the QGSJET, SYBIL, and EPOS hadronic interaction models. Particular attention will be paid to energy scale differences between air fluorescence and ground array observations, lateral particle distribution at the ground, and specific shower observables such as the distributions of primary zenith angles, number of counters per shower, and counter signal strengths