Speaker
Description
Among the most important quantities in fundamental physics for cosmology and beyond standard model theories is the effective mass of the electron (anti-)neutrino, $m_{\nu}$. To date, the most constraining, least model-dependent upper limit on $m_{\nu}$ is set by the KATRIN collaboration with $<450\,\mathrm{meV}/\mathrm{c}^2$ [1]. In complementary experiments by the ECHo [2] and HOLMES [3] collaborations the kinematics of the electron capture decay in $^{163}\mathrm{Ho}$ is investigated by means of microcalorimetry. Ultimately, these experiments anticipate sub-eV limits on $m_{\nu}$, where the exclusion of possible systematic uncertainties is crucial and achieved by a comparison of the calorimetrically measured $Q$-value of the decay to an independently measured one on the same level of uncertainty.
For $^{163}\mathrm{Ho}$ an uncertainty of $0.6 \mathrm{eV}/\mathrm{c}^2$ was achieved in a direct, ultra-precise $Q$-value measurement using the Penning-trap mass spectrometer PENTATRAP which is more than a factor 50 more precise than the previously best measurement [4]. This technique is based on measuring the ratio of the free-space cyclotron frequencies of highly charged ions (HCIs) of the mother and daughter nuclides, the synthetic radioisotope $^{163}\mathrm{Ho}$ and stable $^{163}\mathrm{Dy}$, respectively. In this frequency measurement an unprecedented fractional uncertainty of $3\cdot 10^{-12}$ was reached. The $Q$-value is finally determined from the ratio of the measured cyclotron frequencies and precise atomic physics calculations of the electronic binding energies of the missing electrons in the HCIs.
The poster will focus on the measurement of the electron capture $Q$-value in $^{163}\mathrm{Ho}$ and give an outlook on future measurements that include the nuclides $^{241}\mathrm{Pu}$ and $^{7}\mathrm{Be}$ whose decay spectra are investigated by the Magneto-$\nu$ [5] and BeEST [6] collaborations, respectively, with the aim of placing stringent bounds on the existence of sterile neutrinos.
[1] Aker, M. et al., Science 388, 180 (2025)
[2] Adam, F. et al., arXiv 2509.03423 (2025)
[3] Alpert, B.K. et al., Phys. Rev. Lett. 135, 141801 (2025)
[4] Schweiger, Ch., et al., Nat. Phys. 20, 921, (2024)
[5] Leach, K.G. et al., J. Low. Temp. Phys. 209, 796 (2022)
[6] Lee, C. et al., Phys. Rev. C, accepted (2026)
| Collaboration or Other Affiliation | Other |
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