Baryon magnetic moment (${\mu }_B$)

In the additive ground-state quark model, a baryon magnetic moment is the expectation of ${\sum }_i{Q}_{i}e{\mathbf{\sigma }}_i/(2m_i)$ in its spin-and-flavor wavefunction, with constituent quark masses $m_i$. For a spin-up proton and neutron this gives ${\mu }_p=(4{\mu }_u-{\mu }_d)/3$ and ${\mu }_n=(4{\mu }_d-{\mu }_u)/3$. Approximately equal up and down constituent masses imply ${\mu }_u\simeq -2{\mu }_d$ and ${\mu }_p/{\mu }_n\simeq -3/2$. This is evidence for the valence quark model, not proof that sea quark-antiquark pairs are absent.