Tritium Helium-3 Mass Difference

By trapping and manipulating pairs of ions in a cryogenic Penning trap we are measuring the cyclotron frequency ratios HD$^{\mathrm{+}}$/$^{\mathrm{3}}$He$^{\mathrm{+}}$ and HD$^{\mathrm{+}}$/T$^{\mathrm{+}}$. From these ratios a more precise value for the atomic mass difference between T and $^{\mathrm{3}}$He, and hence the Q-value of tritium beta-decay can be derived. This will enable a strong test of the systematics in the large-scale tritium beta-decay spectrometer KATRIN, which aims for a ten-fold improvement in the laboratory measurement of the electron neutrino mass.