Antimatter in the proton is more down than up

Gao, Haiyan

doi:10.1038/d41586-021-00430-3

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24 February 2021

Antimatter in the proton is more down than up

Protons are found in all atoms, so it might be surprising to learn that they contain antimatter. It now emerges that there is an imbalance in the types of antimatter in the proton — a finding for which there is no agreed theoretical explanation.

Haiyan Gao⁰

Haiyan Gao
1. Haiyan Gao is in the Department of Physics, Duke University, Durham, North Carolina 27708, USA.
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Protons and neutrons, which are collectively known as nucleons, are the building blocks of atomic nuclei and account for more than 99% of the visible matter in the Universe. They are not themselves fundamental particles, but are made up of fundamental constituents called quarks and gluons. There are several types, or ‘flavours’, of quark, the lightest of which — the up and down quarks — are most likely to be found in nucleons. If you could take a snapshot of a proton, you would probably see just three ‘valence’ quarks (two up and one down) inside it. But you might also see gluons, and quark–antiquark pairs (antiquarks are the antimatter counterparts of quarks), transiently appearing and disappearing inside the proton. Writing in Nature, Dove et al.¹ describe their efforts to quantify the probability distributions of different types of antimatter in the proton, and report that down antiquarks are more prevalent than up antiquarks.

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Nature 590, 559-560 (2021)

doi: https://doi.org/10.1038/d41586-021-00430-3

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