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Matter–antimatter symmetry violated

In a mirror world, antiparticles should behave in the same way as particles. But it emerges that leptons — neutrinos, electrons and their more exotic cousins — might not obey this expected pattern.
  1. Silvia Pascoli

    1. Silvia Pascoli is at the Institute for Particle Physics Phenomenology, Department of Physics, Durham University, Durham DH1 3LE, UK.

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  2. Jessica Turner

    1. Jessica Turner is in the Theoretical Physics Department, Fermilab, Batavia, Illinois 60510, USA.

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All visible matter in the Universe is made of fundamental building blocks, the elementary particles. The group of particles known as fermions consists of two types: quarks, which make up protons and neutrons; and leptons, namely, the electron, muon, tau particle and neutrino. For each elementary particle, there is an antiparticle that has the same properties but opposite charge. The best-known example is the antielectron, or positron. It was long thought that antiparticles would behave in the same way as particles in a mirror world made of antimatter, but since the 1960s we have known that quarks and antiquarks break this particle–antiparticle mirror symmetry1,2. Writing in Nature, the T2K Collaboration reports possible findings of violation of this symmetry by leptons3.

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Nature 580, 323-324 (2020)

doi: https://doi.org/10.1038/d41586-020-01000-9

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