With the contribution of a research team led by Prof. Marco Carminati from the Department of Electronics, Information and Bioengineering – Politecnico di Milano, the international KArlsruhe TRItium Neutrino Experiment (KATRIN) at the Karlsruhe Institute of Technology (KIT) has once again surpassed its own achievements. The latest data, recently published in Science, establish an upper limit of 8·10-37 kg (or in scientific language 0.45 eV/c2) for the neutrino mass. With this result, KATRIN, which measures neutrino mass in the laboratory using a model-independent method, has once again set a world record.
Neutrinos are among the most enigmatic particles in the universe. They are omnipresent yet interact extremely rarely with matter. In cosmology, they influence the formation of large-scale galaxy structures, while in particle physics, their minuscule mass serves as an indicator of previously unknown physical processes. Precisely measuring the neutrino mass is therefore essential for a complete understanding of the fundamental laws of nature.
This is precisely where the KATRIN experiment with its international partners comes into play. KATRIN utilizes the beta decay of tritium, an unstable hydrogen isotope, to assess the mass of neutrinos. The energy distribution of the electrons resulting from the decay enables a direct kinematic determination of the neutrino mass.
Achieving this requires highly advanced technical components: the 70-meter-long beamline houses one an intense tritium source, as well as a high-resolution spectrometer with a diameter of 10 meters. This cutting-edge technology allows for unprecedented precision in direct neutrino mass measurements.
The quality of the first datasets has steadily improved since the start of measurements in 2019, and the researchers look optimistically to the future. Measurements of the neutrino mass will continue until the end of 2025. Through the continuous improvement of the experiment and analysis, as well as a larger data set, an even higher sensitivity is expected, and possibly ground-breaking new discoveries.
KATRIN already leads the global field of direct neutrino mass measurements and has surpassed the results of previous experiments by a factor of four with its initial data. The latest findings indicate that neutrinos are at least a million times lighter than electrons, the lightest electrically charged elementary particles. Explaining this enormous mass difference remains a fundamental challenge for theoretical particle physics.
In addition to the precise measurement of the neutrino mass, KATRIN is already planning the next phase. Starting in 2026, a new detector system, TRISTAN, will be installed. Prof. Carminati’s research team has developed the low-noise and high-density readout electronics of the SDD, invented by Prof. Emilio Gatti and realized in monolithic arrays of 166 pixels. This upgrade to the experiment will enable the search for sterile, a hypothetical particle, which interacts even more feebly than the known neutrinos. With a mass in the keV/c² range sterile neutrinos are a potential candidate for dark matter.
