Date:
Tue, 26/06/201812:30-13:30
Hadronic interactions of Ultra-High Energy Cosmic Rays in the Earth’s atmosphere
Abstract: While the major source of Ultra-High Energy Cosmic Rays (UHECR) is not yet identified, it is clear that only a few cosmic particle accelerators are potentially able to reach the required maximal energies of almost 10^21 eV. At these energies UHECR mostly interact with low-energy photons in the source and during propagation. The experimental evidence for a (light) nuclear CR mass composition at Earth complicates the situation. The disintegration of nuclei during transport imposes increased modeling complexity and requires uncertain inputs from nuclear physics, introducing degeneracies in the interpretation of the spectrum in terms of source parameters. Another, probably more severe, problem arises from the modeling of the Extensive Air Showers (EAS) that UHECR generate when interacting with the Earth’s atmosphere. The interpretation of the mass composition is almost entirely model dependent, where the highest uncertainty originates from the modeling of hadronic nucleus-air interactions. The current state-of-the-art event generators for this task are EPOS-LHC, Sibyll 2.3c, QGSJet II-04 and DPMJET-III. At present, however, none of the models succeeds in describing the number of muons that would be expected from the observed electromagnetic component. This implies that data taken with the surface detectors can not be exploited for composition sensitive analyses. In this seminar I will outline the principles of hadronic interaction modeling discussing in higher depth the simplest model – SIBYLL - providing some insight into conceptual and practical differences to the other models. I will also discuss current air shower observations and indirect constraints to review the present situation in this field.
Abstract: While the major source of Ultra-High Energy Cosmic Rays (UHECR) is not yet identified, it is clear that only a few cosmic particle accelerators are potentially able to reach the required maximal energies of almost 10^21 eV. At these energies UHECR mostly interact with low-energy photons in the source and during propagation. The experimental evidence for a (light) nuclear CR mass composition at Earth complicates the situation. The disintegration of nuclei during transport imposes increased modeling complexity and requires uncertain inputs from nuclear physics, introducing degeneracies in the interpretation of the spectrum in terms of source parameters. Another, probably more severe, problem arises from the modeling of the Extensive Air Showers (EAS) that UHECR generate when interacting with the Earth’s atmosphere. The interpretation of the mass composition is almost entirely model dependent, where the highest uncertainty originates from the modeling of hadronic nucleus-air interactions. The current state-of-the-art event generators for this task are EPOS-LHC, Sibyll 2.3c, QGSJet II-04 and DPMJET-III. At present, however, none of the models succeeds in describing the number of muons that would be expected from the observed electromagnetic component. This implies that data taken with the surface detectors can not be exploited for composition sensitive analyses. In this seminar I will outline the principles of hadronic interaction modeling discussing in higher depth the simplest model – SIBYLL - providing some insight into conceptual and practical differences to the other models. I will also discuss current air shower observations and indirect constraints to review the present situation in this field.