Auger-Horizon · A large-scale radio detector for the Pierre Auger cosmic-ray Observatory – precision measurements of ultra-high-energy cosmic rays

Cosmic Rays (ionized atomic nuclei) are the only matter from beyond our solar system or even from extragalactic space, that we can directly investigate. Up to energies of 10^17 eV they most likely originate in our Galaxy. The highest-energy cosmic rays (>10^18 eV) cannot be magnetically bound any more to the Galaxy and are most likely of extragalactic origin.The pure existence of these particles raises the question about their origin – how and where are they accelerated? How do they propagate through the universe and interact? How can we directly probe extragalactic matter and how can we locate its origin? A key to understand the origin of cosmic rays is to measure the particle species (atomic mass). A precise mass measurement will allow discriminating astrophysical models and will clarify the reason for the observed suppression of the cosmic-ray flux at the highest energies, namely the maximum energy of the accelerators or the energy losses during propagation.I address these questions by employing a new technique to precisely measure the cosmic-ray mass composition, which my group pioneered, the radio detection of air showers (induced by high-energy cosmic rays in the atmosphere) on very large scales, detecting horizontal air showers with zenith angles from 60° to 90°. The new set-up will be the world-largest radio array, operated together with the well-established Auger surface and fluorescence detectors, forming a unique set-up to measure the properties of cosmic rays with unprecedented precision for energies above 10^17.5 eV. The radio technique is a cost-effective and robust method to measure the cosmic-ray energy and mass, complementary to established techniques. The energy scale of the radio measurements is established from first principles. The proposed detectors will also enhance the detection capabilities for high-energy neutrinos and the search for new physics through precision measurements of the electromagnetic and muonic shower components.