What is the magnetic dipole moment of a pion?

Question

I'm writing a piece on the nuclear force. My intention was to start with the Yukawa interaction and talk about pions, using them to lead into quarks and gluons and the residual strong force and more. However I've hit a stumbling block, and I'm struggling to find anything online.

I know that the electron magnetic dipole moment is −9284.764 × 10⁻²⁷ J⋅T⁻¹. I know that proton magnetic dipole moment is a 14.10606 × 10⁻²⁷ J⋅T⁻¹. I know that the neutron magnetic dipole moment is −9.662364 × 10⁻²⁷ J⋅T⁻¹. But I can't find anything about the pion magnetic dipole moment. So I have a question: what are the magnetic dipole moments of the charged and neutral pions π⁺ π^- and π⁰?

All answers gratefully received.

Answer 1

It is zero. If the magnetic dipole moment $\boldsymbol \mu$ were different from zero, the particle would have a preferred direction in space, which is not possible for a scalar.

Recall that, in general, $$ \boldsymbol \mu\propto\boldsymbol S $$ which, for a scalar, implies $\boldsymbol\mu\equiv\boldsymbol 0$.