A Heroic Effort to Measure Helium

A Heroic Effort to Measure Helium

After an intricate game of particle jockeying, physicists have now measured the radius of the helium nucleus five times more precisely than before. After banging into enough helium there, a muon will slow down and lose energy—and eventually get trapped by a final helium atom. The muon kicks out both the atom’s electrons, and what’s left is the helium nucleus—which is two protons and two neutrons—and a muon. Next they bathe those ions in laser light, hoping to bump the muons up to a higher-energy but unstable state. “If I were to clean it, I would be putting it into an unstable state because I can’t keep it clean very long.

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