Ghost particles on the scales

What is the mass of a neutrino at rest? A team led by the department of Klaus Blaum, Director at the Max Planck Institute for Nuclear Physics in Heidelberg (MIPK), with the participation of Christoph Düllmann's working group at Johannes Gutenberg University Mainz (JGU), the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, and the Helmholtz Institute Mainz (HIM) has now made an important contribution to the “weighing” of neutrinos as part of the international ECHo collaboration. Using the Pentratrap ion trap, the researchers have achieved an extremely precise measurement of the change in mass of the holmium-163 ion when its nucleus captures an electron and becomes dysprosium-163. From this, the researchers were able to determine this so-called Q value 50 times more accurately than before. With the help of a more precise Q-value, possible systematic errors in the determination of the neutrino mass can be uncovered.

Holmium-163 is an artificial isotope that can be produced by irradiation natural erbium-162 with neutrons, which leads to erbium-163, which in turn decays into holmium-163. The chemical isolation of the produced holmium-163 was carried out at JGU, where the sample tailored to fit the requirements of the Pentatrap experiment in Heidelberg was also produced. Pentatrap consists of five so-called Penning traps. In these traps, electrically charged atoms can be trapped for long times in a combination of a static electric and magnetic field. These ions perform an intricate “circular dance”, which allows their mass to be determined with extreme precision. “With an Airbus A-380 with a maximum load, you could use this sensitivity to determine whether a single drop of water has landed on it,” says Christoph Schweiger, PhD student in Klaus Blaum's department at the Max Planck Institute for Nuclear Physics, illustrating the capabilities of these super scales.

Targets used in the experiment. Left: holmium-163 micro crystals (white flakes in front of dark background) produced in Mainz; right: dysprosium-163 as in PLA-form produced in Heidelberg. (Photo: C. Schweiger / MPIK)


Ion trap PENTATRAP. An extremely precise atomic balance: PENTATRAP consists of five Penning traps arranged one above the other (yellow tower in the middle). In these identically constructed traps, ions in the excited quantum state and in the ground state can be measured in comparison. In order to minimize uncertainties, the ions are also moved back and forth between different traps for comparative measurements. (Photo: MPIK)


Further information

Original Publication:

Direct high-precision Penning-trap measurement of the Q-value of the electron capture in 163Ho for the determination of the electron neutrino mass
Christoph Schweiger, Martin Braß, Vincent Debierre, Menno Door, Holger Dorrer, Christoph E. Düllmann, Christian Enss, Pavel Filianin, Loredana Gastaldo, Zoltán Harman, Maurits W. Haverkort, Jost Herkenhoff, Paul Indelicato, Christoph H. Keitel, Kathrin Kromer, Daniel Lange, Yuri N. Novikov, Dennis Renisch, Alexander Rischka, Rima X. Schüssler, Sergey Eliseev and Klaus Blaum
Nature Physics (2024). DOI: 10.1038/s41567-024-02461-9


Prof. Dr. Christoph E. Düllmann
Johannes-Gutenberg-Universität Mainz
GSI Helmholtzzentrum für Schwerionenforschung GmbH
Helmholtz-Institut Mainz
Phone: +49 6131 39 25852