Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

TL;DR

This study measures the radio emission energy from extensive air showers to serve as a universal, calibration-independent estimator of cosmic-ray energy, aligning with theoretical predictions and the Pierre Auger Observatory's scale.

Contribution

It introduces a method to estimate cosmic-ray energy via radio emission measurements, validated against established energy scales and theoretical models.

Findings

Radiation energy scales quadratically with cosmic-ray energy.

Measured radiation energy is 15.8 MeV at 1 EeV cosmic-ray energy.

Agreement with first-principle calculations confirms the method's validity.

Abstract

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.