Proton spin crisis
Unsolved physics problem / From Wikipedia, the free encyclopedia
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The proton spin crisis (or proton spin puzzle) is a theoretical crisis precipitated by a 1987 experiment by the European Muon Collaboration (EMC),[1] which tried to determine the distribution of spin within the proton.[2]
Unsolved problem in physics:
How do the quarks and gluons carry the spin of protons?
Physicists expected that the quarks carry all a proton's spin. However, not only was the total proton spin carried by quarks far smaller than 100%, these results were consistent with almost zero (4–24%[3]) proton spin being carried by quarks. This surprising and puzzling result was termed the "proton spin crisis".[4] The problem is considered one of the important unsolved problems in physics.[5]