EPOS Model and Ultra High Energy Cosmic Rays

TL;DR

The paper evaluates the EPOS hadronic interaction model within air shower simulations, addressing discrepancies between earlier EPOS results and KASCADE data. It presents EPOS 1.99, which enforces a unified treatment of non-linear effects and forward physics, aligning cross sections with accelerator data and reducing inelasticity. The study demonstrates that EPOS 1.99 yields deeper showers and higher ground-level hadron energy, while increasing muon production due to forward diquark dynamics, suggesting improved—but composition-sensitive—compatibility with KASCADE. Overall, the work shows how forward physics, energy sharing, and non-linear effects shape EAS development and cosmic ray analysis.

Abstract

Interpretation of extensive air showers (EAS) experiments results is strongly based on air shower simulations. The latter being based on hadronic interaction models, any new model can help for the understanding of the nature of cosmic rays. The EPOS model reproducing all major results of existing accelerator data (including detailed data of RHIC experiments) has been introduced in air shower simulation programs CORSIKA and CONEX few years ago. The new EPOS 1.99 has recently been updated taking into account the problem seen in EAS development using EPOS 1.61. We will show in details the relationship between some EPOS hadronic properties and EAS development, as well as the consequences on the model and finally on cosmic ray analysis.

Figures (6)

• Figure 1: Elementary parton-parton scattering: the hard scattering in the middle is preceded by parton emissions attached to remnants. The remnants are an important source of particle production even at RHIC energies.
• Figure 2: Total cross section of proton-carbon interactions. EPOS 1.99, QGSJETII, QGSJET01 and SIBYLL 2.1 hadronic interaction models (lines) are compared to data Dersch:1999zg (points)
• Figure 3: Inelastic cross section of proton-air interactions. EPOS 1.99, QGSJETII, EPOS 1.61 and SIBYLL 2.1 hadronic interaction models (lines) are compared to data of air shower experiment (points).
• Figure 4: a) Each cut Pomeron is regarded as two strings b). c) The most simple and frequent collision configuration has two remnants and only one cut Pomeron represented by two $\mathrm{q}-\overline{\mathrm{q}}$ strings. d) One of the $\overline{\mathrm{q}}$ string ends can be replaced by a $\mathrm{qq}$ string end. e) With the same probability, one of the $\mathrm{q}$ string ends can be replaced by a $\overline{\mathrm{q}}\overline{\mathrm{q}}$ string end.
• Figure 5: Model comparison: longitudinal momentum distributions of pion carbon collisions at 100 GeV from EPOS with (full) or without (dash-dotted) sting-end diquarks and QGSJETII (dashed) compared to data barton.