Proton-air interaction properties at $\sqrt{s}\simeq 100$ TeV from shower-depth measurements with the Pierre Auger Observatory and their connection to the Muon Puzzle

Abstract

Hybrid measurements at the Pierre Auger Observatory indicate that most high-energy hadronic interaction models underestimate the average depth of the shower maximum, $⟨X_{\max }⟩$, at a center-of-mass energy of $\sqrt{s}=97.7\pm 0.4_{-6.2}^{+6.6}\mathrm{TeV}$. In this Letter, the hadronic interaction models are shown to follow a universal relation between the predicted $⟨X_{\max }⟩$ and the mean values of variables characterizing the energy spectra of secondary particles produced in the first interaction of proton-induced air showers. Assuming the validity of these relations in Nature, we map the values of $⟨X_{\max }⟩$ favored by Auger data into mean values of these variables. All models favor an increase in the mean elasticity and in the fraction of hadronic energy in proton--air interactions. The latter must be amplified by a factor of $2.8$ to $4.6$ to account for the muon puzzle.

Submitted to Phys. Rev. Lett