====== 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 [[content:physics:quantum_physics:quarks|quarks]] and their associated 'gluons' (holding them together via the Strong Force) 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 : [[https://en.wikipedia.org/wiki/Proton_spin_crisis|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 [[https://arxiv.org/pdf/1807.05250.pdf|The Spin Structure of the Nucleon]] //Reports on Progress in Physics// Volume 82, Number 7,at arXiv.org

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Also see :[[content:physics:quantum_physics:proton_radius]] , [[content:physics:quantum_physics:proton_mass]] and [[content:physics:quantum_physics:quantum_cheshire_cat]]

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