Speaker
Description
The Project 8 collaboration aims to determine the absolute neutrino mass with a sensitivity of 40 meV/c² by performing Cyclotron Radiation Emission Spectroscopy (CRES) on tritium beta-decay electrons. To achieve the necessary statistics, the experiment is transitioning from waveguide-based detectors to large-volume resonant microwave cavities operating at sub-GHz frequencies. This shift requires a rigorous understanding of how relativistic electrons radiate into the mode structures of a cylindrical cavity, as well as a precise accounting of the noise budget that limits event detection and electron kinetic energy resolution.
We present an analytic framework for characterizing CRES signals in resonant cavities, as detailed in a recent preprint. We derive the power spectral density for an electron undergoing simultaneous cyclotron, axial, and grad-B motion. The model explicitly predicts the sideband structures arising from the Doppler modulation of the axial motion, which are key for accurate event reconstruction and kinematic analysis. We discuss the implications of Purcell enhancement in this geometry and how mode density optimization influences the achievable signal power.
Complementing the signal theory, we introduce a detailed noise model that defines the Signal-to-Noise Ratio (SNR) for the entire readout chain. This model integrates contributions from thermal cavity emissions, boundary losses, and amplifier noise figures. We show that operating the cavity at cryogenic temperatures and radiative cooling are strictly necessary to suppress thermal photon occupation and approach the standard quantum limit. Finally, we outline the roadmap for experimental validation, using demonstrator cavities to verify these SNR predictions and confirm the feasibility of the Phase IV design.