What is your current research topic? Christine Claessens


The most sensitive neutrino scales in the world

Christine Claessens has been a PhD student in Experimental Particle and Astroparticle Physics (ETAP) at the Excellence Cluster PRISMA+ since 2016. In her PhD thesis she is focusing on data analysis and data acquisition for the Project 8 experiment. The Project 8 collaboration recently established Cyclotron Radiation Emission Spectroscopy (CRES) as a novel technique to measure the absolute scale of the neutrino mass with unprecedented precision. In 2016, Christine Claessens visited the University of Washington in Seattle, WA, USA for an extended research stay, during which she was involved in setting up the TRIMS experiment. The TRIMS collaboration has now published an important result in the renowned journal "Physical Reviews Letters". Congratulations on this success!

"In the TRIMS (Tritium Recoil-Ion Mass Spectrometer) experiment, we took a close look at the decay of molecular tritium and measured the branching ratios of different decay channels. We have succeeded in clarifying a long-standing discrepancy between theory and experiment regarding the decay of molecular tritium. This in turn is an important prerequisite for the Project 8 experiment, which I am working on in my doctoral thesis in Mainz, and for the KATRIN experiment at KIT in Karlsruhe.

The aim of Project 8 is to determine the neutrino mass via the decay of tritium and the corresponding decay spectrum. For this purpose, one needs to know the shape of the tritium decay spectrum, which is determined by theoretical calculations, very precisely. The theoretically calculated branching ratios of the individual decay channels have so far contradicted measurements from the 1950s. The TRIMS experiment has now resolved this contradiction and confirmed the theory.

The TRIMS experiment works with a combination of time-of-flight measurements and energy determination after electrostatic acceleration. This information can be used to determine the mass and charge of the incident particles that are produced during tritium decay. When I first came to Seattle, the tests on the prototype had just been successfully completed, and I was able to participate in the construction of the actual experiment.

The focus of my work in Seattle was the characterization of the ion detectors. For this purpose, we measured the capacitance and leakage current of the detectors and detector mounts, assembled a test ion source and recorded the spectrum of an americium-241 source. My tasks further included the installation and commissioning of the magnets that provide the magnetic guiding field for the decay electrons. During a second stay, I also worked closely with the Project 8 team at the University of Washington to set up the data acquisition system for the Project 8 prototype.

Personally, I have benefited greatly from my research stays in Seattle. Much of what I learned while working on the TRIMs setup proved to be directly useful for my work in Mainz. I am very grateful for the great cooperation with the TRIMS team and the enriching experiences I was able to gather. The fact that our work has produced such an important result with great significance for the neutrino mass community and that this result has now been successfully published is very exciting for me."

More than 180 doctoral students and about 100 postdocs are doing research in the various fields of the Mainz Cluster of Excellence PRISMA+. With their commitment, their ideas and their thirst for knowledge, they make an indispensable contribution to the implementation of the PRISMA+ research programme. In the section "What is your current research topic?", we introduce young scientists and their research projects.