Antineutrinos and pentaquarks: it’s hot in Vienna!
« We have been asking questions since 1365 ». This inspiring statement marking the 650th anniversary of the University of Vienna, is hanging near the imposing entrance of its main building. This sign welcomed this morning the 730 physicists who came to Vienna to participate to the main particle physics conference this year organised by the European Physics Society. For a week, the participants will have to choose among hundreds of presentations where the current status of knowledge in particle physics will be presented along with the newest avenues. and we are already making history: Vienna recorded yesterday its highest ever temperature with 39 ˚C.
And this first day brought recent and exciting results. As announced last week, the LHCb collaboration at CERN has discovered the first pentaquarks, composite objects made of five quarks. Quarks are some of the building blocks of matter. Physicists have observed for decades dozens of different particles made of two or three quarks. For example, many particles are made of a pairs of quark and antiquark, while others, like protons and neutrons, contain three quarks. However, in recent years, a few experimental groups also reported the discovery of tetraquarks, objects composed of four quarks. Finally, last week, thanks to the huge dataset made available by the Large Hadron Collider, scientists from the LHCb experiment achieved what many other groups had tried to do for decades without success, and proudly announced the discovery of pentaquarks. Such composite objects were expected but never observed before. It goes to show how much we still have to discover and understand.
Another nice piece of news: the T2K neutrino experiment, which takes place in Japan, may have detected the first signs for oscillations of antineutrinos. To this day, there are three known types of neutrinos, each one accompanying its own particle, namely the electron, the muon and the tau. The oscillation process describes how one type of neutrinos can change into another type. This phenomenon has already been observed for neutrinos, but it would be the first observation for antineutrinos. However, all is far from being set in concrete yet, quite the contrary. With only three events at hands, the T2K team still needs to verify if these events really involve antineutrinos and not just neutrinos. They therefore need to collect more date for another year or two before this issue can be settled. If it turns out to be indeed antineutrinos, we would learn more on the similarities or the differences between matter and antimatter.
Several experiments are also trying to establish if there could also be another type of neutrinos, called sterile neutrinos. Their spin would be the opposite of known neutrinos, meaning they would be spinning on themselves in the opposite direction. Clearly, any new type of particle is something worth watching for. The confirmation of the existence of sterile neutrinos would send a shock wave in particle physics since it would constitute an indisputable proof for the existence of a theory more encompassing than the current theoretical model, called the Standard Model. Everything would then have to be rethought. And who knows? Physicists could very well have enough to keep asking difficult questions for another 650 years…
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