= Baryon magnetic moment
{title2=$\mu_B$}
In the additive ground-state <quark model>, a <baryon> <magnetic moment> is the expectation of $\sum_i Q_i e\boldsymbol\sigma_i/(2m_i)$ 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.
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