====== Neutron CP problem ======

//The neutron CP problem// is a disparity between the Standard Model (SM) view of particle physics, and theoretical aspects of Quantum Chromo Dynamics (QCD).

The neutron (as the name implies) has a neutral electrical 'charge', because the three[[content:physics:quantum_physics:quarks]]from which it is formed have fractional positive and negative charges which add to //exactly //zero. No experimental measurements to-date have shown anything other than a non-zero charge. This is in conflict with the highly-robust QCD theory, which insists that Charge and Parity (CP) would //not be zero// under all conditions.

A theoretical particle, the [[https://en.wikipedia.org/wiki/Axion|Axion,]]  was proposed in 1977 as a possible way of resolving the problem. To date, it has not been detected in any experiment.

Further reading [[http://web.mit.edu/redingtn/www/netadv/Xneutron.html|MIT]]

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Also see : [[content:physics:quantum_physics:electron_quark_balence]]