# Statistics of the radiating relativistic electrons

## TL;DR

This paper introduces a statistical method to analyze the evolution of relativistic electron energy spectra undergoing small quantum losses, revealing how spectra broaden over time and impact radiation generation.

## Contribution

A general statistical framework for describing the evolution of electron spectra with small quantum losses, including convolution-based modeling and spectral width analysis.

## Key findings

- Electron spectra initially show individual recoil characteristics.
- Spectral width increases with recoil number following a power law.
- Broader spectra limit coherent radiation in high-energy regions.

## Abstract

We developed a general method for assessing the evolution of the energy spectrum of relativistic charged particles that have undergone small quantum losses, such as the ionization losses when the electrons pass through matter and the radiation losses in the periodic fields. These processes are characterized by a small magnitude of the recoil quantum as compared with the particle's initial energy. We convey the statistical consideration of the radiating electrons. We demonstrate that in the initial stage, the electron's spectrum can be described as a composition of consecutive convolutions of the recoil spectrum with itself, taken with the Poisson mass. In this stage, at the relatively small average number of the recoils, the electron spectrum reveals some individual characteristics of the recoil spectrum. Furthermore, the spectrum loses individuality and allows for proximate description in the terms of statistical parameters. The results of this consideration reveal that the width of the electron spectrum is increasing with the number of recoils according to the power law, with the power index being inverse to the stability parameter, which gradually increases with the number of recoils from one to two. Increase of the spectrum width limits the ability of the beam to generate coherent radiation in hard x-ray and gamma-ray region.