In search of the axion, a hypothetical elementary particle

For some time now, physicists have been thinking about an elementary particle that has very little mass, no electric charge and no spin (quantum angular momentum). It would interact very little with other particles because of these properties and would therefore be a good candidate for dark matter, which is characterized by just that. But the axion is also used in physics because in the neutron, a neutral nuclear particle, the charge of the quarks of which it is composed is so perfectly distribu...