Abstract
We demonstrate that the shower-to-shower fluctuations of the muon content of extensive air showers correlate with the fluctuations of a variable of the first interaction of Ultra High Energy Cosmic Rays, which is computed from the fraction of energy carried by the hadrons that sustain the hadronic cascade. The influence of subsequent stages of the shower development is found to play a sub-dominant role. As a consequence, the shower-to-shower distribution of the muon content is a direct probe of the hadron energy spectrum of interactions beyond those reachable in human-made accelerators.
Highlights
Ultra-High-Energy Cosmic Rays (UHECRs) collide with nuclei of the Earth’s atmosphere at center-of-mass energies that surpass the Large Hadron Collider (LHC) energy scale, creating huge cascades of particles, the Extensive Air Showers (EAS) [1]
We demonstrate that the fluctuations of the muon content of EAS directly correlate with the fluctuations of a variable that probes the hadron energy spectrum of the first interaction
This variable is computed from the fraction of energy carried by the hadronic particles that sustain the hadronic cascade, being a direct probe of the hadron energy spectrum
Summary
Ultra-High-Energy Cosmic Rays (UHECRs) collide with nuclei of the Earth’s atmosphere at center-of-mass energies that surpass the LHC energy scale, creating huge cascades of particles, the Extensive Air Showers (EAS) [1]. The precise composition of UHECR is still unknown, as the nature of the primaries has to be inferred from EAS measurements themselves by using phenomenological models of the hadronic interactions tuned to a limited range in energy and kinematic phase-space. Breaking this degeneracy is one of the challenges currently faced by UHECR physics. Measurements at the Pierre Auger Observatory have shown that simulations, using the LHC-tuned hadronic interaction models, underestimate the muon content in air showers [2, 3]. The subsequent shower interactions give the overall scale of the muon content, but play a sub-dominant role in the shower-to-shower fluctuations
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