Elementary particle quarks—now considered elementary particles. And within a molecule, the electron's three degrees of freedom (charge, spin, orbital) can separate via the wavefunction into three quasiparticles (holon, spinon, orbiton). Yet a free electron—which is not orbiting an atomic nucleus and lacks orbital motion—appears unsplittable and remains regarded as an elementary particle. Around 1980, an elementary particle's status as indeed elementary—an "ultimate constituent" of substance—was mostly discarded for a more practical outlook, embodied in particle physics' Standard Model, what's known as science's most experimentally successful theory. Many elaborations upon and theories beyond the Standard Model, including the popular supersymmetry, double the number
Charge radius This asymmetric distribution of charge within the particle gives rise to a small negative squared charge radius for the particle as a whole. But, this is only the simplest of a variety of theoretical models, some of which are more elaborate, that are used to explain this property of a neutron. For deuterons and higher nuclei, it is conventional to distinguish between the scattering charge radius, "r" (obtained from scattering data), and the bound-state charge radius, "R", which includes the Darwin–Foldy term to account for the behaviour of the anomalous magnetic moment in an electromagnetic field and which is appropriate