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I read Georgi's Lie algebras in Particle Physics 2nd chap5 and have two questions.

1) In the beginning he mentioned Heisenberg regarded neutron is composed as proton and electron, the force between nucleons are exchanging electrons. My question is, what is the experimental evidence falsifies this idea (except proton proton scattering in accelerators)?

2) In p81, he built multiparticle states by successively adding creation operators

[tex]a^{\dagger}_{N,1/2,\alpha_1} \cdots a^{\dagger}_{N,1/2,\alpha_n} | 0 >[/tex]

My question is, is that just a basis of multiparticle eigenstate of Hamiltonian? Imagine there is a vacuum. I first created a helium nuclei, then add a single electron. When I add the second electron, the helium electronic eigenstate will not be a tensor product of two single-electron state. The tensor product is just a two-electron (plus a nuclei) basis. Back to the equation of multiparticle state, is that just a basis?

Similarly for many hadrons, like [tex]u\bar{d}[/tex], is that a basis or a notation means the pion contains [tex]u[/tex] and [tex]\bar{d}[/tex]?

Thank you very much in advance

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# Two questions about isospin

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