Particle physics in cosmic rays

TL;DR

This paper discusses how the Pierre Auger Observatory's measurements of ultra-high energy cosmic rays provide insights into hadronic interactions at energies beyond current accelerators, advancing understanding of particle physics and cosmic ray composition.

Contribution

It presents new analyses of air shower data to constrain high-energy hadronic interaction models and explore particle physics at energies exceeding those of the LHC.

Findings

Probing interactions at center-of-mass energies up to 400 TeV.

Enhanced understanding of muon production in air showers.

Constraints on hadronic models from cosmic ray data.

Abstract

The Pierre Auger Observatory is the world's largest detector of ultra--high energy cosmic rays (UHECRs). It uses an array of fluorescence telescopes and particle detectors at the ground to obtain detailed measurements of the energy spectrum, mass composition and arrival directions of primary cosmic rays (above the energy of $10^{17}$ eV) with accuracy not attainable until now.Observations of extensive air showers performed by the Pierre Auger Observatory can also be used to probe hadronic interactions at high energy, in a kinematic and energy region not accessible by man-made accelerators. Indeed, exploiting Auger data, we reach center-of-mass energies up to 400 TeV, i.e. more than 30 times of those attainable at the LHC, and explore interactions in the very forward region of phase space on targets of atomic mass of 14. In addition, a precise measurement of the muon component of air showers at the ground is more sensitive to the details of the hadronic interactions along many steps of the cascade development, such as the multiplicity of the secondaries and the fraction of electromagnetic component with respect to the total signal. On the other hand, the intrinsic muon fluctuations mostly depend on the first interaction. In this paper we overview the new Auger studies exploring the connection between the dynamics of the air shower and the multi-particle production, and how this knowledge can be translated into constraints of the high energy hadronic models as well as direct measurements, complementary to, and beyond the reach of, accelerator experiments.