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Particles and interactions

Particles and interactions

The spin of a proton

04 Jun 2015
Taken from the June 2015 issue of Physics World

For the best part of 30 years physicists have been unable to answer a seemingly simple question: where does proton spin come from? As Edwin Cartlidge reports, the answer may finally be within reach

Artwork depicting the proton as a composite particle composed of two fuzzy blue up quarks and one fuzzy red down quark, with bits of red and blue scattered across the background
Not so simple The spins of the two up quarks and one down quark that make up a proton add up to about a third of the proton's spin, so where is the rest of that spin coming from? (Courtesy: ARCSCIMED/Science Photo Library)
In physics, the budget always has to be balanced. The amount of any physical quantity on one side of

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Edwin Cartlidge is a science writer based in Rome, Italy, e-mail edwin.cartlidge@yahoo.com
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