June 2022
Shy neutrinos on the scales
“I'm working on the Project 8 experiment, with which we want to measure the neutrino mass directly. To do this, we use the beta decay of tritium – an unstable hydrogen isotope – into a helium isotope, an electron and a neutrino. Project 8 is backed by an international collaboration. In Mainz, we are investigating how to build a tritium source for the later experiment.
Neutrinos are ubiquitous particles and we have known about them for quite a long time. In the standard model of particle physics, neutrinos have no mass at all – similar to the light particles, the photons. However, experiments have shown that neutrinos do have mass.
©: Angelika Stehle
But why don't we know the mass of neutrinos yet? Because they hardly interact with matter at all. That's why we call them ghost particles. So we have to be very clever and have come up with a new technique at Project 8: CRES or Cyclotron Radiation Emission Spectroscopy. We measure the energy of the electrons produced by the beta decay of tritium via their orbital frequency in a magnetic field.
Using a mini version of the experiment, we have already been able to show that the CRES technique works. We are currently developing a tritium source for the subsequent large experiment. A special aspect is that we need individual tritium atoms for this - which we generate from the fission of tritium molecules. As tritium is highly radioactive, we are initially developing a similar but safer source. For this purpose, we are using “normal” hydrogen in Mainz, which we can now break down into individual atoms very well. As soon as we are able to generate a beam from these hydrogen atoms, we can transfer the technology to tritium. The work we are doing now is part of a five-year research and development program that will serve as the basis for the final Project 8 experiment.
Neutrino physics fascinates me because mass is such a fundamental property and yet we still don't know it. What I particularly like about physics in Mainz is that Bachelor students are already intensively involved in current research projects. This allows female students in particular to learn from role models at a very early stage.”
Dr. Larisa Thorne is a postdoc in the group of Professor Martin Fertl. She came to neutrino physics rather by chance, after a detour via a nuclear physics topic. She completed her PhD with a thesis on the KATRIN neutrino experiment and started as a postdoc in Mainz two weeks after her PhD exam in July 2021.