Explaining muon excess in cosmic rays using the gluon condensation model

Abstract

Ultrahigh-energy cosmic rays are often characterized indirectly by analyzing the properties of secondary cosmic ray particles produced in the collisions with air nuclei. The particle number $N_{\mu }$ of muon and the depth of shower maximum $X_{\max }$ after air shower cascade are mostly studied to infer the energy and mass of the incident cosmic rays. Research have shown that there is a significant excess in the observed number of muons arriving at the ground from extensive air showers (EAS) compared to the simulations using the existing cosmic ray hadronic interaction model. To explain this muon excess phenomenon, a new theoretical model, the gluon condensation model (GC model), is introduced in this paper and simulated by using the AIRES engine. We assume that the GC effect appears mainly in the first collision of the cascade leading to a significant increase in the strangeness production, consequently, the production rate of kaons is increased and $n_K/n_{\pi }$ is greater than the value of the usual hadronic interaction process. In the calculation, the model assumes that only pions and kaons are produced in GC state. The increase of strange particle yield would mean that the energy transferred from the hadronic cascade to electromagnetic cascade through ${\pi }^0\to 2\gamma$ decay is reduced. This would in turn increase the number of muons at the ground level due to meson decays.Our model provides a new theoretical possibility to explain the muon excess puzzle.

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