Event reconstruction for sub-eV energy resolution in the Project 8 neutrino mass experiment

Cyclotron Radiation Emission Spectroscopy (CRES) is a technique for measuring the energy of single electrons by detecting the cyclotron radiation they emit in a magnetic field. The Project 8 experiment is pioneering CRES to measure the energy spectrum of beta electrons emitted in the decay of tritium, with the goal of improving sensitivity to the neutrino mass. Following the collaboration's first upper limit on the neutrino mass from its Phase II experiment, it has been developing technology to achieve a final sensitivity of 0.04 eV. The current prototype, the Cavity CRES Apparatus (CCA), will be the first CRES detector with resonant cavity geometry, enabling scalability, improved energy resolution, and event-by-event magnetic field corrections. An electron in a magnetic trap will undergo axial in addition to cyclotron motion, resulting in a modulation of the cyclotron frequency at the axial frequency. This gives information about the field experienced by each electron. I will give an overview of how we hope to attain 0.3 eV root mean square (rms) energy resolution in the CCA by detecting this modulation. Then, I will give a survey of algorithms under development for electron event reconstruction, including matched filter and machine learning based approaches.