The elusive and somehow still mysterious the neutrino could one day provide new insight on physics beyond the standard model of particle physics.
Targeting a combination of the mass of the three known neutrinos, KATRIN (Karlsruhe TRItium Neutrino experiment) observes the radioactive decay of tritium during which an electron and a neutrino (of electronic flavor) are released. In rare cases, the electron takes almost all the available kinetic energy. Only the energy of the neutrino at rest, associated with its mass, is thus missing. It is this tiny deficit that is measured in the gigantic scale embedding a high purity tritium gas source.
In addition, the beta decay of tritium also allows to search for the possible trace of a 4th type of neutrinos (sterile) possibly able to transform, during their propagation, into one of the three flavors of neutrinos, while remaining insensitive to the weak interaction (radioactivity, nuclear fusion, etc.). The existence of one or more additional neutrino families could explain anomalies observed by Irfu researchers on nuclear reactor neutrinos.
How did the KATRIN researchers proceed? Among the 60 billion electrons emitted by the tritium source each second, only 2 million - in particular those whose energy is close to the maximum energy of the beta spectrum - are selected for analysis. The expected signature of sterile neutrinos is a kinked structure in the smooth spectrum of these electrons.
No significant sterile neutrino signal was observed in the mass range of about 2 to 40 eV observable in KATRIN (broader than that of < 10 eV reactor neutrinos). This result draws new exclusion limits wider than those determined by previous comparable experiments in Mainz (Germany) and Troitsk (Russia) in the late 1990s.
A scientist from Irfu coordinated the analysis of the spectra for the KATRIN collaboration, establishing an innovative data analysis strategy. In collaboration with the Max Planck Institut für Physik (Munich), he also developed a new analysis chain, using the covariance matrix approach to study and propagate systematic errors and their correlations.
The international KATRIN experiment, which brings together twenty research institutes from seven countries, is hosted at the Karlsruhe Institute of Technology (KIT) in Germany.