Speaker
Description
Among the most important quantities for fundamental physics is the effective mass of the electron neutrino $m_{\nu}$, which has far-ranging consequences for cosmology and theories beyond the Standard Model. At present, the most precise indirect upper limit on $m_{\nu}$ is <120 meV/$c^2$ resulting from astrophysical observations while the most precise direct limit is set by the KATRIN collaboration with <0.8 meV/${c^2}$, based on the kinematic study of the tritium $\beta$-decay. Complementary, the ECHo and HOLMES collaborations investigate the electron capture decay in $^{163}\mathrm{Ho}$ using microcalorimeters. In order to reach the anticipated sub-eV limits on $m_{\nu}$ with calorimetric measurements, the exclusion of possible systematic uncertainties is crucial and is achieved by a comparison of the calorimetrically determined $Q$-value of the decay to an independently measured one with the same uncertainty level. Within this talk, an independent, direct, ultra-precise measurement of this $Q$-value using the Penning-trap mass spectrometer Pentatrap is presented with a sub-eV uncertainty. Using this technique, the $Q$-value is determined by measuring the ratio of the free cyclotron frequencies of highly charged ions of the mother and daughter nuclides, the synthetic radioisotope $^{163}\mathrm{Ho}$ and $^{163}\mathrm{Dy}$, respectively. The $Q$-value is finally determined from the measured ratio of free cyclotron frequencies by including precise atomic physics calculations of the electronic binding energies of the missing electrons in the measured highly charged ions. This more than 40-fold improved $Q$-value compared to the previous best direct measurement paves the way for a sub-eV upper limit on $m_{\nu}$ within the ECHo and HOLMES collaborations.
