The Nobel to Takaaki Kajita and Arthur B. McDonald – The Point

In the second day of the week of Nobel, the famous Swedish jury awarded the Nobel Prize in physics. This year, this prestigious award is jointly attributed to Japanese Takaaki Kajita – professor at Tokyo University and director of the Institute for Research on cosmic rays – and the Canadian Arthur B. McDonald – professor emeritus at Queen’s University Kingston in Canada – for their discovery of neutrino oscillation, which shows that these elementary particles devoid of electric charge, are well contrary to what was originally thought, a mass, although small

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But what is it that a neutrino oscillation? This is a phenomenon of quantum mechanics in which the elusive particle is transformed. In nature, scientists believe that neutrinos exist in three forms, very poetically called “flavors”. Thus there are electronic neutrinos, muon and tau. But it’s not so simple … For what Takaaki Kajita and Arthur B. McDonald showed, is that they propagate through space at nearly the speed of light, neutrinos can pass from a flavor to another.

task even more difficult as these particles, because they interact very little with matter, are incredibly complicated to detect. Thus, 10 billion neutrinos that pass through the Earth, one will interact with an atom of our planet. A consequence of the absence of electrical charge that allows them to play very easily pass walls.

Men and particle detectors

In 1998, each separately with his team, Takaaki Kajita and Arthur B. McDonald managed to demonstrate that neutrinos oscillated, ie that, along the way, they could change their nature. . A hypothesis in the late 50s by an Italian-British-Soviet physicist named Bruno Pontecorvo

Takaaki Kajita worked on atmospheric neutrino collision byproducts of cosmic rays – which we continually bombarded from all over the universe – and molecules in the atmosphere of Earth. Neutrinos who rely on us, on all sides, in a perfectly constant flow. Except that counting neutrino detector in their past in Japan, the scientist and his team were not the same number as they reached the top or bottom. Explanation? Neutrinos from below, unlike those falling from the sky, had gone through all the Earth to get to Japan. And, having thus traveled a much greater distance, a greater proportion of them had had time to change into another form of neutrinos than that détectaient researchers.

Meanwhile, Team Arthur B. McDonald planchait on solar neutrinos, produced by our star, as a detector with a large heavy-water pool, inherited research conducted bomb during World War II. A plant whose greatest merit was to detect several types of solar neutrinos, not just all having original “flavor” electronics, but also those that have changed in nature. Which then enabled them to show, as in previous experiments, that only 50% of solar neutrinos arriving on Earth, in the form of electron neutrinos, but the remaining 50% had not disappeared. They had only changed “flavor”, so that other experiments were unable to detect them.

Better understanding of matter and the universe

The discovery of the neutrino oscillation is experimental but also theoretical interest, as it involves non-nullity of the mass of the particle, which has amended the so-called standard model of physics, namely the set of laws which describes the interactions between the different particles. According to the Nobel Committee, it is a discovery “historic” likely to enable a better understanding of the inner workings of matter, and therefore of the Universe. Just that!

“We particularly the idea that neutrino oscillations could open the way to explaining the disappearance of antimatter in the universe. Indeed, starting from the Big Bang, there were as many particles as antiparticles. But today we live in a world that is made of particles only, so material, not antimatter. But where is this big bang antimatter? Maybe that neutrinos oscillate and ability could be an explanation … “says Jacques Dumarchez, specializing in neutrino oscillations, nuclear and high energy physics laboratory (LPNHE) of the National Institute of Nuclear Physics and Physics particles (CNRS / University Pierre and Marie Curie / University Paris-Diderot).

The predictions foiled

As for the Nobel jury, choosing Takaaki Kajita and Arthur B. McDonald, it was once again upset the odds which were rather to the pioneers in the field of ultra-short lasers, Canadian Paul Corkum and German Ferenc Krausz. Last year, the famous Swedish jury rewarded the Japanese Isamu Akasaki and Hiroshi Amano and American Shuji Nakamura for their invention in the 1990s, light emitting diode (LED) emitting efficiency with blue light, which had opened the way to become well known white LED. Recall that the Nobel comes with a reward of eight million Swedish kronor (about 855,000 euros), divided between each of the winners if there are more.