Accelerator measurements of magnetically-induced radio emission from particle cascades with applications to cosmic-ray air showers

TL;DR

This study validates electrodynamics simulations of radio emissions from particle cascades in magnetic fields, crucial for understanding cosmic-ray air showers, through controlled laboratory experiments at SLAC.

Contribution

First laboratory measurements confirming that simulations accurately model magnetically-induced radio emission in dielectric media for cosmic-ray air shower analysis.

Findings

Simulations match experimental data within uncertainties.

Radio emission forms a cone peaking at the Cherenkov angle.

Linear relationship between magnetic field strength and emission intensity.

Abstract

For fifty years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An experiment at SLAC provides a beam test of radio-frequency (RF) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experiment provides a suite of controlled laboratory measurements to compare to particle-level simulations of RF emission, which are relied upon in ultra-high-energy cosmic-ray air shower detection. We compare simulations to data for intensity, linearity with magnetic field, angular distribution, polarization, and spectral content. In particular, we confirm modern predictions that the magnetically induced emission in a dielectric forms a cone that peaks at the Cherenkov angle and show that the simulations reproduce the data within systematic uncertainties.