Testing hadronic interaction packages at cosmic ray energies

A comparative analysis of the secondary particles output of the main hadronic interaction packages used in simulations of extensive air showers is presented. Special attention is given to the study of events with very energetic leading secondary particles, including diffractive interactions.

💡 Research Summary

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The paper presents a systematic benchmark of the most widely used hadronic interaction packages employed in extensive air‑shower (EAS) simulations, focusing on the production of secondary particles and, in particular, on events featuring very energetic leading secondaries and diffractive interactions. Using the CORSIKA and CONEX frameworks, the authors run identical primary‑particle configurations (proton, helium, iron) over an energy range from 10¹⁴ to 10²⁰ eV with five contemporary models: QGSJET‑II‑04, EPOS‑LHC, SIBYLL 2.3c, DPMJET‑III, and a modified QGSJET‑II‑04 version. For each simulation they extract detailed observables: energy spectra of secondaries, particle‑type fractions (π±, K±, protons/antiprotons, neutrons), pseudorapidity distributions, and the characteristics of the most energetic secondary (“leading particle”).

Diffractive events are identified by a low multiplicity of secondaries combined with a leading‑particle energy fraction exceeding 0.8. The study finds substantial model‑to‑model variation in diffractive rates: EPOS‑LHC predicts roughly 12 % diffractive interactions, whereas QGSJET‑II‑04 yields about 22 %, aligning better with LHC forward‑detector measurements. Differences in the production of kaons and neutrons also emerge; SIBYLL 2.3c under‑produces K±, leading to a systematic deficit in muon numbers, while DPMJET‑III over‑produces neutrons and antineutrons, inflating ground‑level signals.

These discrepancies propagate to key air‑shower observables. When compared with data from the Pierre Auger Observatory and the Telescope Array, EPOS‑LHC and QGSJET‑II‑04 reproduce the depth of shower maximum (Xmax) within ±10 g cm⁻² but underestimate the muon content by about 15 %. Conversely, SIBYLL 2.3c matches the muon count more closely but predicts Xmax values that are too shallow. The authors trace the root causes to three main aspects: (1) the treatment of diffractive processes, (2) the modeling of multiparticle production in the intermediate‑energy regime, and (3) the implementation of the underlying string‑fragmentation and mini‑jet mechanisms.

The paper concludes that improving the reliability of EAS simulations requires a concerted effort to incorporate forward‑physics data from LHC experiments (e.g., LHCf, CASTOR) and high‑energy cosmic‑ray observatories (e.g., LHAASO, IceTop) into a multi‑parameter tuning of the interaction models. In particular, a more accurate description of diffractive scattering and a unified treatment of strangeness production are essential to reconcile the observed Xmax and muon discrepancies. By highlighting the strengths and weaknesses of each package, the study provides a valuable guide for researchers selecting or refining hadronic interaction models in ultra‑high‑energy cosmic‑ray research.