Project 8 and Neutrino Mass Measurements at Penn State
L. de Viveiros, Pennsylvania State University (Principal Investigator)
The neutrino mass is one of the most important open questions in physics. The most sensitive direct searches for the neutrino mass rely on the beta decay method: beta decays emit an electron and a neutrino, and thanks to energy conservation, one can determine the mass of the neutrino from the shape of the electron spectrum near its endpoint. The Project 8 experiment has developed a novel technique called Cyclotron Radiation Emission Spectroscopy (CRES) to precisely measure the beta decay spectrum in tritium, and thus obtain a neutrino mass measurement with sensitivity surpassing that of existing experiments. An electron trapped in a uniform magnetic field will emit cyclotron radiation with frequency that depends on its kinetic energy, so that a measurement of the radiation provides a nondestructive electron energy measurement. The Project 8 collaboration has already demonstrated the viability of this technique using a small-scale (~10 cm3) prototype. However, an attempt at measuring the neutrino mass will require a vast increase in the number of tritium decays, which can be accomplished through an increase in detector volume to 10-100 m3. The use of atomic tritium in large volumes will necessitate the use of lower magnetic fields, and thus lower cyclotron frequencies, to the range of ≤ 1 GHz; and it will also result in an increase in complexity of certain techniques, such as antenna arrays. Our group has worked on developing the concept of an open-ended, mode-filtered resonant cavity as the ideal strategy for measuring CRES signals. This project will explore the use of resonant cavities for CRES at 1 GHz and below, and the optimization of mode filtering and readout for precise signal reconstruction. We will develop methods for calibration, triggering, acquisition, and analysis of cavity CRES signals. This project will produce a medium-scale cavity to perform the first low-frequency cavity CRES measurements to demonstrate the capabilities of this technology. We will then produce the design of the cavity and signal acquisition system for a Pilot-Scale Atomic Tritium CRES Experiment with a source volume on the order of 1 m3, a template that can be replicated to reach the scale required for a neutrino mass measurement. The successful completion of this project will extend the functionality of the CRES technique to large scales, providing essential tools and support that will allow Project 8 to move into the next phases of its experimental program, and lead to the ultimate neutrino mass experiment.
