Mass composition working group report

¹ Physics Department, University of Utah, USA
² University of Adelaide, Adelaide, S.A. 5005, Australia
³ Yu. G. Shafer Institute for Cosmophysical Research and Aeronomy, 31 Lenin Ave., 677980 Yakutsk, Russia
⁴ Universidade de São Paulo, Instituto de Física de São Carlos, SP, Brazil
⁵ Institute for Cosmic Ray Research, the University of Tokyo, Kashiwa, Chiba 277-8582, Japan
⁶ Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro Tokyo 152-8550, Japan
⁷ Karlsruhe Institute of Technology, Campus North, Institut für Kernphysik, Karlsruhe, Germany

^a e-mail: jbellido@physics.adelaide.edu.au

Abstract

We present a summary of the measurements of mass sensitive parameters at the highest cosmic ray energies done by several experiments. The X_max distribution as a function of energy has been measured with fluorescence telescopes by the HiRes, TA and Auger experiments and with Cherenkov light detectors by Yakutsk. The 〈X_max〉 or the average mass (〈lnA〉) has been also inferred using ground detectors, such as muon and water Cherenkov detectors. We discuss the different data analyses elaborated by each collaboration in order to extract the relevant information. Special attention is given to the different approaches used in the analysis of the data measured by fluorescence detectors in order to take into account detector biases. We present a careful analysis of the stability and performance of each analysis. The results of the different experiments will be compared and the discrepancies or agreements will be quantified.