Physicists finally nail the proton’s size

In 2010, Randolf Pohl of the Max Planck Institute of Quantum Optics (Quantamagazine) announced his team precisely measured the size of the proton by substituting the electron of a hydrogen atom by a muon. The size of the proton in presence of the muon was smaller than with an electron which would imply unknown physical interactions between protons and muons.

A team led by Eric Hessels of York University in Toronto has remeasured the proton in regular hydrogen. Finally, the proton’s radius is around 0.833 femtometer, a measurement exactly consistent with Pohl’s value. The proton does not change size depending on context! (Quantamagazine)

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