The Free-Space CRES demonstrator for Phase III of the Project 8 neutrino mass experiment

The Project 8 experiment aims to directly measure the neutrino mass down to ∼40 meV/c² by reconstructing the kinematics of tritium beta decay, using a novel technique called Cyclotron Radiation Emission Spectroscopy (CRES). The operating principle is to put tritium in a uniform magnetic field, causing the emitted electron to undergo cyclotron motion and radiate. Measuring the electron’s radiation frequency yields its energy, and the energy spectrum constrains the mass of the neutrino involved in the decay. This method has been demonstrated in a small waveguide, but needs to be scaled to a larger volume to improve neutrino mass sensitivity. The next phase of this experiment will be done in a medical MRI magnet with an array of antennas viewing a volume of gaseous molecular tritium. Detection is challenging because a single electron emits <1 fW at ∼26 GHz in a 1 T field, and exhibits complex spectral features due to its motion. This talk will describe the major subsystems of the Free-space CRES Demonstrator (FSCD), and discuss recent efforts in simulation, event reconstruction, and experimental R&D on the path towards a full detector design.