When did neutrinos start?

Midwife of matter

"He was badly hit. The power supply and water cooling were almost completely destroyed."

The shock of the Japanese physicist Koichiro Nishikawa is still in the bones. Because when the great earthquake raged in his country in March, his research equipment was also severely damaged - a particle accelerator in Tokai, 200 kilometers from the epicenter. It was only in 2010 that Nishikawa and his team started their experiment - a spectacular experiment.

"Our accelerator shoots hydrogen nuclei at a target. This creates short-lived particles, so-called mesons. They quickly decay again and emit a beam of neutrinos in the process. These neutrinos fly 300 kilometers into the Japanese Alps, where they hit an underground detector, a giant tank filled with 20,000 tons of water. The neutrinos can interact with this water. And that's how we can detect them. "

T2K, that's the name of the experiment, because the neutrinos fly from Tokai to Kamioka, where the water tank is built into a former mine. Ultimately, the researchers would like to find out what role neutrinos played in the Big Bang and whether they might act as obstetricians for matter. But this can only have been possible if neutrinos have a very specific property - if they can transform from one kind, so-called muon neutrinos, into another kind, into electron neutrinos. And although the quake stopped the experiment for the time being, the physicists are able to present an initial result. Nishikawa:

"We have indications that electron neutrinos are actually showing up in our water tank; there have been six so far. However, we need more data to be able to speak of a discovery."

And T2K will be able to deliver them again soon, because:

"We've fixed almost everything. In a few months we'll start the experiment again."

And the Japanese experiment should soon be supported by an experiment in Europe.

"The Double Chooz experiment is an experiment that has been set up on a nuclear reactor in France and has just started taking data," "

says Stefan Schönert, physics professor at the Technical University of Munich and co-experimenter in France.

"" "A nuclear reactor emits neutrinos with enormous intensity. And we then measure these neutrinos in a detector. We want to see whether this neutrino changes on the way between production in the reactor and the detector."

A principle similar to that in Japan, only with a nuclear reactor instead of an accelerator. Schönert:

"We think that by the end of this year we will have measured enough events to confirm or disprove the T2K experiment."

If the results are confirmed, another phenomenon should also exist for abstract theoretical reasons - namely that neutrinos behave differently than their antiparticles, the antineutrinos. And that could even have cosmic consequences in the end, says Stavros Katsanevas from the French research organization CNRS.

"At the beginning of the universe, immediately after the Big Bang, the following may have happened: At that time, exotic neutrinos and antineutrinos could have existed for a short time, both with very large mass. Both then decayed again very quickly, and the neutrinos in a different way than the antineutrinos. This asymmetry has led to the creation of more matter than antimatter - which is why our world is made up of matter, whereas antimatter seems to have disappeared. And there could indeed be something about this theory - provided the results from Japan are confirmed. "

To solve the riddle, however, new experiments will have to be built - real neutrino factories that generate stronger neutrino beams than before and direct them to significantly larger detectors.