Why the Proton 'Lost Weight' and Then 'Gained It Back' ⚡ экспресс
In 2010, scientists measured the size of the proton using muonic hydrogen—a hydrogen atom where the electron is replaced by a muon, its heavier twin. The value was significantly smaller than the one obtained from ordinary hydrogen and electron scattering. This discrepancy hinted at a possible violation of lepton universality, the principle that electrons and muons should behave identically except for mass. Recent experiments have resolved the mismatch, showing that the proton's size is the same regardless of the probe. The proton radius puzzle has been laid to rest.
To uncover the proton's true size, physicists swapped the electron in a hydrogen atom for its heavy copy—the muon. Acting like a magnifying glass with thousandfold power, the muon gets right up against the nucleus and 'probes' the proton with unprecedented precision. Spectral analysis revealed the proton to be roughly 4% smaller than earlier experiments with ordinary electrons suggested.
This challenged the Standard Model and its principle of lepton universality—the notion that all light particles follow the same electric laws. Two different magnifying glasses seemed to paint conflicting pictures of a single object.
But re-examining the old data exposed a flaw. The electron-based 'magnifying glass' harbored an unnoticed error: it slightly distorted the image. After recalibration, both glasses agreed on the same size. The puzzle dissolved; physics stood firm.
🎯 The muon decays in 2 microseconds. Light travels only 600 meters in that time. Yet it's enough for muonic hydrogen to yield the most precise proton size measurement in history.