Particle Interactions in Matter at the Terascale: the Cosmic-Ray Experience

TL;DR

This paper discusses high-energy particle interactions in matter, focusing on cosmic rays and astrophysical neutrinos, highlighting phenomena like the LPM effect, hadronic showers, and particle propagation at energies up to 10^20 eV.

Contribution

It provides an overview of particle interaction behaviors at ultra-high energies, emphasizing the effects on electromagnetic and hadronic showers, with insights from cosmic-ray observations.

Findings

Suppression of bremsstrahlung and pair production at high energies due to LPM effect

Transition to hadronic-dominated showers above 10^20 eV

Cosmic-ray data supports slow increase of hadronic cross-section with energy

Abstract

Cosmic-rays with energies up to $3\times10^{20}$ eV have been observed, as have as have astrophysical neutrinos with energies above 1 PeV. In this talk, I will discuss some of the unique phenomena that occur when particles with TeV energies and above interact with matter. The emphasis will be on lepton interactions. The cross-sections for electron bremsstrahlung and photon pair conversion are suppressed at high energies, by the Landau-Pomeranchuk-Migdal (LPM) effect, lengthening electromagnetic showers. At still higher energies (above $10^{20}$ eV), photonuclear and electronuclear interactions dominate, and showers become predominantly hadronic. Muons interact much less strongly, so can travel long distances through solids before losing energy. Tau leptons behave similarly, although their short livetime limits how far they can travel. The hadronic interaction cross-section is believed to continue to increase slowly with rising energy; measurements of cosmic-ray air showers support this prediction.