First Observation of Cyclotron Radiation from MeV-Scale e± following Nuclear β Decay

We present an apparatus for detection of cyclotron radiation yielding a frequency-based beta(+/-) kinetic energy determination in the 5 keV to 2.1 MeV range, characteristic of nuclear beta decays. The cyclotron frequency of the radiating beta particles in a magnetic field is used to determine the beta energy precisely. Our work establishes the foundation to apply the cyclotron radiation emission spectroscopy (CRES) technique, developed by the Project 8 Collaboration, far beyond the 18-keV tritium endpoint region. We report initial measurements of beta(-)'s from He-6 , beta(-)'s from Ne-19 decays to demonstrate the broadband response of our detection system and assess potential systematic uncertainties for beta spectroscopy over the full (MeV) energy range. To our knowledge, this is the first direct observation of cyclotron radiation from individual highly relativistic beta's in a waveguide. This work establishes the application of CRES to a variety of nuclei, opening its reach to searches for new physics beyond the TeV scale via precision beta-decay measurements.

Automated summary

A new apparatus for detecting cyclotron radiation is introduced, which allows for precise determination of the energy of beta particles. The study demonstrates the potential application of the cyclotron radiation emission spectroscopy (CRES) technique beyond its initial range, and presents initial measurements of beta particles from He-6 and Ne-19 decays. The observed radiation from highly relativistic beta particles in a waveguide represents a significant advancement in the field.