Detection of Inclined Extensive Air Showers with the Pierre Auger Observatory

Junior Research Group of Dr. Markus Roth

Searching exotic particles at highest eneriges

Cosmic rays with energies exceeding 10²⁰ eV have been detected since 1963.  They confront us with some of the most interesting and challenging questions in science today: Where do they come from?  What kind of particles are they?  How can they be accelerated to energies larger than 10²⁰eV? What can we learn about cosmic objects, large-scale structure and magnetic fields?  What can they teach us about particle interactions at these otherwise inaccessible energies, which reach 450 TeV in the center-of-mass system?

Forschungszentrum Karlsruhe, a member of the Hermann von Helmholtz Association of National Research Centres (HGF), and the University of Karlsruhe play a key role in the Pierre Auger Observatory, which is designed to detect cosmic rays of highest energies and thereby shed light on the questions posed above.

In this context, the aim of the Helmholtz-University Young Investigators Group VH-NG-128, founded in 2005, is the investigation of inclined air showers, or showers with arrival directions larger than 60° in zenith.  Since the Auger observatory was in its start-up phase in 2005, the pursuit of this ambitious objective lead to contribution across a broad range of topics, from service work to published data analysis. The main activities are described below.

To enable data analysis it was necessary to have a complete software infrastructure for event simulation and reconstruction.  Our group plays a key role in developing and setting up the Offline software, which is now in a mature state and is widely used for a variety of data analyses by the collaboration at large.

With the required tools in place, we next developed techniques for reconstructing showers below 60° (known as vertical showers). A measurement of the vertical energy spectrum of cosmic rays above 2.5x10¹⁸eV has been published, and constitutes one of the most important milestones for the Auger observatory.

Based on our experience analysing vertical showers, we developed, together with other groups, a reconstruction of inclined showers. The energy spectrum obtained with this reconstruction is consistent with the result from other groups within the Collaboration and
agrees with the independently measured spectrum of vertical showers.

Study of inclined showers leads naturally to the development of techniques to hunt for neutrino induced showers, which can be disentangled from background only at high zenith angles. The group developed a new Monte Carlo approach for detailed simulation of neutrinos propagating through the Earth and contributes to the Auger task searching for neutrinos.

Many of the methods devised to distinguish neutrino induced showers are also applicable to the problem of determining the mass composition. Ground array observables used in the neutrino analysis were correlated with the composition-sensitive depth of shower maximum measured with the fluorescence detector.

All of our analyses make extensive use of large simulation libraries to study systematic uncertainties, statistical accuracies and especially to provide reference patterns for statistical inference. External funding was obtainefrom the special initiative funds of the Helmholtz president to set up a large computing cluster which is now integrated in the GRID virtual organisation VO-Auger.