Mainz 2014 – scientific programme

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T: Fachverband Teilchenphysik

T 28: Kosmische Strahlung 1

T 28.4: Talk

Monday, March 24, 2014, 17:35–17:50, P5

Mass Composition Analysis Using Elongation Rate — •Livingstone Ochilo, Markus Risse, and Alexey Yushkov for the Pierre Auger collaboration — University of Siegen, Siegen , Germany

The all-particle cosmic ray energy spectrum has been observed to flatten at around 5.2× 10¹⁸ eV where the spectral index changes from γ=3.2 to γ=2.6, a feature called the ”ankle" of the spectrum. Cosmic rays with energy around the ankle and beyond, known as ultra-high energy cosmic rays (UHECR), have a very low flux and reconstruction of their properties from extensive air shower measurements is subject to uncertainties for instance from hadronic interaction models. Since the year 2004, the Pierre Auger Observatory has recorded a considerable number of UHECR events beyond the ankle. With the greatly improved statistics, the mass composition of the extreme end of the cosmic ray energy spectrum is now being investigated with improved accuracy. The measured composition of UHECR is an important parameter in validating the models used to explain their sources and acceleration mechanisms. In this study, we will perform a mass composition analysis using elongation rate (the rate of change of the depth of shower maximum with energy), measured by the fluorescence detector of the Pierre Auger Observatory. The advantage of this approach is a weak dependence of the results on the choice of the hadronic interaction models. Gefördert durch die BMBF-Verbundforschung Astroteilchenphysik.