The spectra and composition of Ultra High Energy Cosmic Rays and the measurement of the proton-air cross section

Abstract

The shape of the longitudinal development of the showers generated in the atmosphere by very high energy cosmic ray particles encodes information about the mass composition of the flux, and about the properties of hadronic interactions that control the shower development. Studies of the energy dependence of the average and width of the depth of maximum distribution of showers with $E\gtrsim 10^{17.3}$ eV measured by the Pierre Auger Observatory, suggest, on the basis of a comparison with current models, that the composition of the cosmic ray flux undergoes a very important evolution, first becoming lighter and then rapidly heavier. These conclusions, if confirmed, would have profound and very surprising implications for our understanding of the high energy astrophysical sources. Studies of the shape of the depth of maximum distribution in the same energy range have been used by Auger and by the Telescope Array Collaboration to measure the interaction length of protons in air, a quantity that allows to estimate the $pp$ cross sections for values of $\sqrt{s}$ well above the LHC range. In this paper we argue that it is desirable to combine the studies of the cosmic ray composition with those aimed at the measurement of the $p$--air cross section. The latter allow to obtain estimates for the fraction of protons in the flux that can be of great help in decoding the composition and its energy dependence. Studies that consider multiple parameters to characterize the depth of maximum distributions also offer the possibility to perform more sensitive tests of the validity of the models used to describe high energy showers.

39 pages, 19 figures

References in corpus (13)

• Depth of Maximum of Air-Shower Profiles at the Pierre Auger Observatory: Measurements at Energies above 10^17.8 eV
• Measurement of the proton-air cross-section at $\sqrt{s}=57$ TeV with the Pierre Auger Observatory
• The Cosmic Ray Energy Spectrum Observed with the Surface Detector of the Telescope Array Experiment
• Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory
• Measurement of the cosmic-ray energy spectrum above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Features of the energy spectrum of cosmic rays above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
• First measurement of elastic, inelastic and total cross-section at $\sqrt{s}=13$ TeV by TOTEM and overview of cross-section data at LHC energies
• Extragalactic cosmic rays diffusing from two populations of sources
• Measurement of the Proton-Air Cross Section with Telescope Array's Black Rock Mesa and Long Ridge Fluorescence Detectors, and Surface Array in Hybrid Mode
• Depth of maximum of air-shower profiles: testing the compatibility of measurements performed at the Pierre Auger Observatory and the Telescope Array experiment
• Determination of the proton-to-helium ratio in cosmic rays at ultra-high energies from the tail of the $X_{\max }$ distribution
• Highlights from the Pierre Auger Observatory (ICRC2019)

Cited by in corpus (6)

• Measurement of the Depth of Maximum of Air-Shower Profiles with energies between $10^{18.5}$ and $10^{20}$ eV using the Surface Detector of the Pierre Auger Observatory and Deep Learning
• Determination of the Cosmic-Ray Chemical Composition: Open Issues and Prospects
• Scaling violation in interaction of cosmic ray hadrons and the nature of the 3 PeV knee in the spectrum of primary cosmic rays
• Learning the Composition of Ultra High Energy Cosmic Rays
• Bose-Einstein condensation and muon production in ultra-high energy cosmic ray particle collisions
• A new basic air shower observable sensitive to the cosmic-ray elemental mass