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The proton (red) — has a radius of 0.84 femtometers (fm). Also shown in the figure are the three quarks that make up the proton and the gluons that hold them together. (Dr. Yong-Hui Lin/University of Bonn)
Germany: Particle Physics

Are Protons Even Smaller Than We Thought?

A few years ago, a novel measurement technique showed that protons are probably smaller than had been assumed since the 1990s. The discrepancy surprised the scientific community. Physicists at the University of Bonn and the Technical University of Darmstadt have now developed a method that allows them to analyze the results of older and more recent experiments much more comprehensively than before.

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