Characteristics of High Energy Particle Interactions from the Study of Irregular Air Showers
Since the discovery of cosmic rays about one century ago, there have been two main approaches in their experimental study. The first is analyzing their arrival directions, energies, and composition in order to determine the nature of their source or sources. The second is analysis of their interactions in the atmosphere to learn about the structure of elementary particles through the characteristics of their collisions at extremely high energy. The energy available in the collisions of cosmic ray protons with atmospheric nuclei exceeds greatly that achieved or achievable in any man-made accelerators. The study of these interactions may reveal the existence of new, exotic particle states, as well as the details of particle structure. The Pierre Auger Observatory is the largest cosmic ray experiment ever constructed. It records air shower data from the interactions of primary cosmic ray particles with energies from 1018eV to beyond 1020eV. The interaction energies of these events exceed the LHC at CERN by one to two orders of magnitude. I have developed a new method that seeks to identify leading particles with long tracks emerging from the primary interaction. The technique characterizes the properties of the leading particles, giving information on inelasticity and cross-section in a regime well beyond current accelerator data. The method identifies events with irregular air shower development. These events are compared to expectations from CONEX air shower simulations using the current event generator QGSJET-II. To eliminate background events, real-time data on cloud cover at the site are employed. We have measured the interaction length for the leading particles with mean energy near 1018eV. Based on the predicted leading particle composition in QGSJET-II, we have determined an interaction length for protons. The method does not find any irregular air showers in simulations of iron primaries. The analysis demonstrates the proton primaries are present in the cosmic rays at these energies.
air shower, shower age, contamination, cloud, Cherenkov
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