Determining the neutrino mass with cyclotron radiation emission spectroscopy—Project 8

The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron radiation emission spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with O(eV) resolution. A lower bound of m(νe) ≳ 9(0.1) meV is set by observations of neutrino oscillations, while the KATRIN experiment-the current-generation tritium beta-decay experiment that is based on magnetic adiabatic collimation with an electrostatic (MAC-E) filter-will achieve a sensitivity of m(νe) ≲ 0.2 eV. The CRES technique aims to avoid the difficulties in scaling up a MAC-E filter-based experiment to achieve a lower mass sensitivity. In this paper we review the current status of the CRES technique and describe Project 8, a phased absolute neutrino mass experiment that has the potential to reach sensitivities down to m(νe) ≲ 40 meV using an atomic tritium source.United States. Department of Energy (Grant DE-SC0011091