This project is designed to determine the mass of the electron neutrino from observation of the end point of the beta-decay spectrum of molecular tritium. The current limit on neutrino mass from this technique is around 2 eV/c2, but this result appears to be dominated by systematic uncertainties. The mass is expected to be at least an order of magnitude less than this value, possibly around 0.2 eV/c2. NEXTEX proposes to make this end point observation using purely electrostatic analysis of the electrons produced in the beta decays, unlike the previous measurements and KATRIN, the experiment that is expected to provide the next major step in accuracy, all of which utilized magnetic analysis of the electrons resulting from the beta decay. Additional features of the NEXTEX apparatus include use of an electron gun to calibrate the apparatus to better than 1 eV via observation of the electron diffraction pattern produced at its detector location. The proposed accuracy of NEXTEX is better than 0.8 eV/c2 for the mass of the electron neutrino. Thus NEXTEX is not expected to achieve the accuracy of KATRIN, which is designed to provide an accuracy of 0.2 eV/c2. However, NEXTEX may well produce a measurement sooner than can KATRIN, and it may produce important identifications of systematic uncertainties that are difficult to anticipate until the measurements are extended below present levels of accuracy.
NEXTEX is a collaboration of 6 universities, and is headed by the group at the University of Texas. Thus it involves several graduate students in its efforts. Its broader impacts certainly include the impact it will have on fundamental physics by providing a new limit on the mass of the electron neutrino as obtained from direct measurement.
