Assertion: neutron | /r/HasAspect | a slightly higher
Facets:
value: due to isospin breaking
type: CAUSE
value: slightly
type: DEGREE
Source sentences:
text: Although the neutron does in fact have a slightly higher mass due to isospin breaking (this is now understood to be due to the difference in the masses of the up and down quarks and the effects of the electromagnetic interaction), the appearance of an approximate symmetry is useful even if it does not exactly hold; the small symmetry breakings can be described by a perturbation theory, which gives rise to slight differences between the near-degenerate states.