Muon Production in Relativistic Cosmic-Ray Interactions

TL;DR

This paper reviews high-energy muon production in cosmic-ray interactions, highlighting how muon data can reveal cosmic-ray composition and test high-energy particle physics models, especially with upcoming detector capabilities.

Contribution

It discusses muon production data, interprets it with soft models, and projects future measurements with IceCube and Km3Net to explore high-$p_T$ regimes.

Findings

Muon spectra measured by MACRO show high-energy cosmic-ray interactions.

IceCube and Km3Net will extend muon $p_T$ measurements into perturbative QCD regimes.

Muon data can complement collider experiments in understanding cosmic-ray composition.

Abstract

Cosmic-rays with energies up to $3\times10^{20}$ eV have been observed. The nuclear composition of these cosmic rays is unknown but if the incident nuclei are protons then the corresponding center of mass energy is $\sqrt{s_{nn}} = 700$ TeV. High energy muons can be used to probe the composition of these incident nuclei. The energy spectra of high-energy ($>$ 1 TeV) cosmic ray induced muons have been measured with deep underground or under-ice detectors. These muons come from pion and kaon decays and from charm production in the atmosphere. Terrestrial experiments are most sensitive to far-forward muons so the production rates are sensitive to high-$x$ partons in the incident nucleus and low-$x$ partons in the nitrogen/oxygen targets. Muon measurements can complement the central-particle data collected at colliders. This paper will review muon production data and discuss some non-perturbative (soft) models that have been used to interpret the data. I will show measurements of TeV muon transverse momentum ($p_T$) spectra in cosmic-ray air showers from MACRO, and describe how the IceCube neutrino observatory and the proposed Km3Net detector will extend these measurements to a higher $p_T$ region where perturbative QCD should apply. With a 1 km$^2$ surface area, the full IceCube detector should observe hundreds of muons/year with $p_T$ in the pQCD regime.