Session 2WB: New Directions in Beta Decay II

Cyclotron Radiation Emission Spectroscopy and results from Phase II of the Project 8 neutrino mass experiment

Measurements of the β^- spectrum of tritium give the most precise directly measured limits on neutrino mass. Cyclotron Radiation Emission Spectroscopy (CRES) is a new experimental technique that has the potential to surmount the systematic and statistical limitations of current-generation direct measurement methods and reach an effective electron antineutrino mass sensitivity of ∽40 meV/c². I will introduce CRES and report on Phase II of Project 8's neutrino mass experiment, including the Bayesian and frequentist analyses leading to its first tritium endpoint and neutrino mass limit results. I will also discuss our stringent background limit, with no events detected above the endpoint, and our demonstration of high resolution.   

New Developments in the CRES Technique for Neutrino Mass Measurement

The Project 8 Collaboration is developing next generation technology for neutrino mass measurement based on the Cyclotron Radiation Emission Spectroscopy (CRES) technique. Recently, Project 8 has for the first time used the CRES technique to measure the tritium beta-decay spectrum endpoint and place an upper limit on the absolute scale of the neutrino masses. Future progress towards the Project 8 collaboration's goal of measuring the neutrino mass scale with a sensitivity of 40 meV will require novel technologies for performing CRES in a multi-cubic-meter volume, using magnetically trapped tritium atoms. The Project 8 collaboration has been exploring phased antenna arrays as a technology for performing CRES in large volumes. However, recent progress has revealed that a large RF cavity, with a resonant frequency in the 300 MHz - 1 GHz range, represents a solution for a next-generation neutrino mass experiment with potentially significantly reduced complexity and cost. In my talk, I will introduce the new technologies being developed by the Project 8 experiment to enable CRES measurements in large volumes. First, I will introduce the antenna array approach to CRES and highlight areas of recent progress. Second, I will give a detailed introduction to: the cavity-based CRES concept, the preliminary designs for the RF cavity and signal readout, and the reconstruction algorithms that will enable the next generation of CRES-based experiments in resonant cavities. Finally, I will give an overview of the plans for a set of cavity demonstrator experiments, which set the path towards a 40 meV sensitivity neutrino mass measurement.   

$^6$He-CRES: Experimental Overview and Recent Progress

The $^6$He-CRES experiment at the University of Washington CENPA aims to precisely measure the Fierz coefficient $b_{fierz}$ which parameterizes exotic currents in the weak interaction representing a violation of SM physics. A measurement of bFierz with a $10^{-3}$ uncertainty would be competitive with current LHC searches for tensor currents. 

The decay of $^6{\rm He}$ has a large endpoint ($Q(^6{\rm He})\approx 3.5\,MeV$) which allows for the $m/E$ distortion, expected from a non-zero $b_{fierz}$ coefficient, to vary by about a factor of 7 over the spectrum, leading to high sensitivity. We use Cyclotron Radiation Emission Spectroscopy (CRES), a technique first demonstrated by the Project 8 collaboration aiming at a determination of the neutrino mass via a measurement of the $^3{\rm H}$ beta spectrum. The technique determines the beta energy by measuring the frequency of the cyclotron radiation of betas in a magnetic field. The $^6$He-CRES experiment will have high energy resolution and be shielded from systematics that affect traditional means of electron spectroscopy. A high level overview of the CRES technique will be followed by a discussion of preliminary results.