Single electron detection and spectroscopy via relativistic cyclotron radiation

TL;DR

This paper reports the first direct observation of single-electron cyclotron radiation, enabling precise energy measurements crucial for neutrino mass research.

Contribution

It introduces a novel radiofrequency spectrometer capable of detecting single-electron cyclotron radiation from relativistic electrons, advancing beta spectroscopy techniques.

Findings

Single-electron cyclotron radiation detected directly.

Relativistic frequency shift allows precise electron energy measurement.

Potential application in neutrino mass experiments.

Abstract

It has been understood since 1897 that accelerating charges must emit electromagnetic radiation. Cyclotron radiation, the particular form of radiation emitted by an electron orbiting in a magnetic field, was first derived in 1904. Despite the simplicity of this concept, and the enormous utility of electron spectroscopy in nuclear and particle physics, single-electron cyclotron radiation has never been observed directly. Here we demonstrate single-electron detection in a novel radiofrequency spec- trometer. We observe the cyclotron radiation emitted by individual magnetically-trapped electrons that are produced with mildly-relativistic energies by a gaseous radioactive source. The relativistic shift in the cyclotron frequency permits a precise electron energy measurement. Precise beta elec- tron spectroscopy from gaseous radiation sources is a key technique in modern efforts to measure the neutrino mass via the tritium decay endpoint, and this work demonstrates a fundamentally new approach to precision beta spectroscopy for future neutrino mass experiments.