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Sunday, July 25, 2010

Protons get a wee bit smaller


New measurements show that the charge radius of a proton is not 0.8768 femtometers, as previously thought, but is instead only 0.8418 femtometers. As I'm sure you all know, a femtometer is one quadrillionth of a meter, or 10-15 of a meter. To get an idea of how small this is, click on the graphic in this previous ‘Just for fun’ post. Randolf Pohl of the Max Planck Institute led an international team of physicists in revising the proton measurement.

Getting the new, more accurate measurement involved several months of preparation and data collection. Without going into too much detail, they replaced the sole electron in a hydrogen atom with the much larger muon, and then used a laser to excite the muon into a more energetic sphere. The energy difference between the two orbitals correlates directly with the size of the nucleus.

Obviously, the measurements involved were incredibly small. To give you an idea of the precision required, the physicists had to create a laser that could fire in only 900 billionths of a second in order to get the results they needed.

If this data is confirmed, it means that some of the predictions of quantum electrodynamics will need to be recalculated. This could send repercussions throughout the physics community.