Speaker
Description
Ultra-high-energy cosmic rays have long been recognized as a unique opportunity to access hadronic interactions at centre-of-mass energies and forward kinematics far beyond those achievable at collider experiments. In this talk, we present a framework that establishes, for the first time, a direct and physically interpretable link between hadron production in the primary interaction and correlated fluctuations of air-shower observables.
By introducing a compact set of production variables constructed from the energy spectra of secondary particles in the first interaction, we show that a linear combination of these variables, $\xi$, captures the dominant fluctuations of the depth of shower maximum, $\Delta X_{\rm max}$. The causal connection between $\xi$ and $\Delta X_{\rm max}$ enables the construction of a probabilistic mapping that predicts the moments of the $X_{\rm max}$ distribution in a model-independent way, with biases well below current experimental uncertainties.
Building on this approach, we further show that the depth of shower maximum and the muon content of extensive air showers jointly encode how the primary energy is distributed among secondary particles. These features can be accessed through a probabilistic description that isolates sensitivity to hadronic physics in the initial collision, while treating the subsequent shower development as effectively universal.
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