Neutrino Mass Experiment at The University of Texas at Austin (NEXTEX)

NEXTEX is the next generation experiment designed to determine the electron antineutrino mass to at least 0.5 eV. The experiment is based on the shape of the beta endpoint energy spectrum from gaseous tritium molecules. Two high throughput electrostatic differential electron analyzers coupled with spherical deflection accelerator are key components of the apparatus. The voltages at the electrodes of the spectrometers ultimately determine the energy of the electrons reaching the detector. The correlations between voltages and the energy of the transmitted electrons will be calibrated with diffraction on the T2 gas of electrons emitted from the auxiliary gun. The coherent electron diffraction pattern from T2 will provide a series of calibration markers for the spectrum with uncertainties better than 100 mV. Extremely low background count-rates from cosmic rates of less than one count a day at the detector has been already demonstrated. A numerical model predicts residual background from tritium sources of few counts per day. The tritium source and its recycling system is designed to prevent the formation of HT to better than 1% during the fiduciary runs.