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Uh oh, the size of a proton may be significantly smaller than originally believed

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Laser measuring device

A team of scientists at Swiss Federal Institute of Technology have upset the current body of literature on quantum electrodynamics by proving that the size of a proton is actually much smaller than originally believed. Their measurements indicated the proton’s radius measures a mere 0.84fm.

Unlike an electron or neutrino, which are fundamental particles that behave like points, a proton is a messy collection of quarks, gluons, and virtual particles that occupies what should be a measurable amount of space. Within experimental error, various measurements of the proton’s size have all put it about 0.88 femtometers (a fm is 10-15 meters). The team of Swiss researchers, working at a particle accelerator in Switzerland, found a different way of measuring the proton’s size.  They put a muon—a heavy, unstable, relative of the electron—in orbit around a proton creating an atom called muonic hydrogen, which can be measured during the brief time it exists before the muon decays. Those measurements have produced a new, very high-precision value for the proton’s radius which could have a profound impact on quantum physics.

In addition to the proton radium anomaly, the other, and potentially most exciting, possibility discovered through their efforts is that muons interact with protons in a fundamentally different way than electrons. That shouldn’t be the case, and if it actually turns out to be, then it’s a sign there must be some new physics out there.