First Observation of Cyclotron Radiation from MeV-Scale ${e}^{\ifmmode\pm\else\textpm\fi{}}$ following Nuclear $\ensuremath{\beta}$ Decay

First Observation of Cyclotron Radiation from MeV-Scale $e^{\pm}$ following Nuclear $β$ Decay

W. Byron et al. (He6-CRES Collaboration)

Phys. Rev. Lett. 131, 082502 – Published 23 August 2023

Abstract

We present an apparatus for detection of cyclotron radiation yielding a frequency-based $β^{\pm}$ kinetic energy determination in the 5 keV to 2.1 MeV range, characteristic of nuclear $β$ decays. The cyclotron frequency of the radiating $β$ particles in a magnetic field is used to determine the $β$ 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 $β^{-}$ ’s from ${}^{6}{He}$ and $β^{+}$ ’s from ${}^{19}{Ne}$ decays to demonstrate the broadband response of our detection system and assess potential systematic uncertainties for $β$ spectroscopy over the full (MeV) energy range. To our knowledge, this is the first direct observation of cyclotron radiation from individual highly relativistic $β$ ’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 $β$ -decay measurements.