The proton has lost a little of its bulk. A fresh attempt to pin down its mass, with three times the precision of the previous best try, finds that the subatomic particle is 30 billionths of a per cent lighter than we thought.
All atoms contain at least one proton, which means measurements of its simplest characteristics – its size, charge and mass – can help answer some of the big questions in physics, including why the universe contains more matter than antimatter.
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