Stars and galaxies, and everything in between that makes up our everyday lives exist because they are made up of matter. Matter consists of sub-atomic particles such as electrons, quarks and neutrinos, and for each particle there is a corresponding counterpart made of antimatter, creating “antiparticles”. According to this theory, the Big Bang should have created matter and antimatter in equal amounts, but today the Universe is made up of far more matter than antimatter.
Researchers from the University of Sheffield, as part of an international group of more than 350 scientists in the T2K Collaboration, have taken a step towards answering why there is so much more matter than antimatter. The study was published in Nature and took place in Japan, utilising the SuperKamiokande detector to observe neutrinos (matter) and antineutrinos (their antimatter counterparts), which were generated 295km away at the Japanese Proton Accelerator Research Complex (J-PARC). Physicists believe that a difference (asymmetry) in the physical properties of neutrinos and antineutrinos might help us understand why the universe is predominantly made of matter.
“Astronomers find that the matter in the universe is overwhelmingly just that: matter, with positively charged atomic nuclei surrounded by negative electrons,” said Professor Lee Thompson, of the University of Sheffield’s Department of Physics and Astronomy.
“When particle physicists make new particles in accelerators, they always find that they produce particle-antiparticle pairs: for every negative electron, a positively charged positron. So why isn’t the universe 50 per cent antimatter? This is a long-standing problem in cosmology – what happened to the antimatter?
“This work brings together particle physics and cosmology – by studying neutrinos, the most elusive of the elementary particles, we learn something about the largest of astrophysical topics, the universe itself.”
The next-generation neutrino experiment DUNE, currently being constructed in a mine in South Dakota, might detect the effect of CP violation in neutrinos faster than expected. This could bring us closer to creating a model that explains how the Universe evolved to become mostly made of matter.


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