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Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

The Proton Spin Crisis

'Spin' is an intrinsic property of many subatomic particles - it's been likened in some ways to the 'angular momentum' of a spinning ball, - but more accurately is a mathematical 'vector' or 'property'.

After the discovery that protons are composed of three quarks and their associated 'gluons', it was assumed that the proton's spin property must be derived from the 'spin' of its constituent quarks.

A 1987 experiment at CERN (which has subsequently been replicated by other experiments) showed that this is not the case. It's now thought that the quarks only contribute between 4% and 24%.

This surprising and puzzling result was termed the “proton spin crisis”. The problem is considered one of the important unsolved problems in physics.
Source : Wikipedia

Note that the as yet unexplained anomaly also applies to the Neutron, which is also built from three quarks.

For a technical description, see The Spin Structure of the Nucleon Reports on Progress in Physics Volume 82, Number 7,at arXiv.org


Also see :Proton radius puzzleplugin-autotooltip__plain plugin-autotooltip_bigProton radius puzzle

Until 2010, measurements (backed up by theory) had put the radius of the proton at about 0.87 femtometres, but in that year, experiments at the Max Planck Institute of Quantum Optics in Germany found a 4% discrepancy.

And in 2016, new experiments …

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