Numerical study of the composition of ultra-high-energy cosmic rays

Several experiments around the world, like the ground-based observatories Pierre Auger and Telescope Array, and soon the space telescope JEM-EUSO, are investigating ultra-high-energy cosmic rays, trying to solve the mystery of their origin. The mass composition of these particles is a key piece of information crucial for a better understanding of the problem. Yet it cannot be observed directly but rather inferred from the simultaneous measure of the energy E-0 of the primary particle and the atmospheric depth X-max of its shower maximum. The conversion of (E-0, X-max) into a primary mass can only be achieved by air-shower simulation. The paper investigates this question through detailed Monte Carlo calculations of air showers initiated by ultra-high-energy cosmic rays of 10(18)-10(20) eV. The calculations were carried out using the code CONEX in combination with different up-to-date hadronic interaction models. The obtained results are compared to the most recent data from the current experiments.