Development of Resonant Cavities for Project 8 Neutrino Mass Experiment

Although neutrinos were long assumed to be massless, the existence of neutrino mass has now been experimentally established. The actual value of the neutrino mass remains an unknown - an outstanding question with implications across particle physics, cosmology, and the Standard Model. The Project 8 Experiment aims to determine the mass of neutrinos by using a novel technique called Cyclotron Radiation Emission Spectroscopy (CRES) to measure the energy spectrum of electrons produced in tritium beta decays, with higher resolution than previous experiments. CRES measures the coherent radiation emitted by electrons as they undergo cyclotron motion in a strong magnetic field. The emitted radiation correlates directly with the kinetic energy of the electrons, and is collected using a resonant cavity. We characterized a 6 GHz open-ended cylindrical cavity to assess the efficiency of different cavity design features and RF signal readout systems. We utilized the bead-puller perturbation technique, which involves moving a small dielectric bead through the cavity and measuring resulting shifts in the resonant frequency with a vector network analyzer (VNA), allowing the creation of 3D maps of the electromagnetic fields. A machine learning model was trained on environmental data and used to correct for systematic fluctuations. Accurate characterization of the cavity RF signal response and field maps are essential for interpreting CRES data and advancing the experiment's sensitivity to the neutrino mass.