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I read that the magnetic moment of the proton can be expressed as the sum of the magnetic moments of the three quarks like $\mu_p = \frac{4}{3}\mu_u - \frac{1}{3}\mu_d$. But I couldn't find a table listing the measured magnetic moments of the quarks. Can you point me to a reference?

Qmechanic
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asmaier
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2 Answers2

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Since a quark $q_i$ is a spin $\frac{1}{2}$ Dirac particle with charge $z_i e$ and constituent mass $m_i$ with $i=u,d,s...$ theory predicts its magnetic moment as

$ \mu_i = \frac{z_i e \hbar}{2 m_i}$.

Note that the formula in your question is only valid in the constituent quark model where a baryon consists only of three constituent quarks. Therefore you have to use the constituent quark mass in the formula for the magnetic moment too. A list of constituent quark masses is eg. found here. These masses are obtained from hadron spectroscopy.

I am not aware of any direct measurements of quark magnetic moments.

Johannes
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Quarks are confined.

Any "measurements" come from the measurements of seen particles, utilizing the Dirac equation, Quantum Field Theory and the symmetries of the standard model to constrain the quantities of the quarks, be it masses or moments or charges.

The standard model was extremely well verified by the measurements at LEP up to the energies of LEP.

anna v
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