Deuteron is p-n so naively should have zero electric quadrupole moment. However, experimentally it turns out quite large: 0.2859 e⋅fm2 from https://en.wikipedia.org/wiki/Deuterium#Magnetic_and_electric_multipoles
This Wikipedia article explains it by adding l=2 angular momentum states - should we imagine it as a hidden dynamics?
Maybe as oscillations between 'pn' and 'np' by some pi+ exchange? (but shouldn't it make it a linear antenna producing EM waves?)
To describe e.g. deuteron-proton scatterings they neglect quark structure, but require three-body force ( https://en.wikipedia.org/wiki/Three-body_force) - would including quarks into considerations allow to focus only on two-body forces?
But what happens with quarks when biding proton and neutron into deuteron? I am working on soliton particle model ( https://www.dropbox.com/s/aj6tu93n04rcgra/soliton.pdf ) suggesting that there is a shift of charge from proton to neutron for binding of deuteron, like uud-udd slightly shifting quark u toward right, d toward left - is such explanation of quadrupole moment allowed (e.g. by QCD)?
Deuterium actually has one of the smallest quadrupole moments.
The nucleus cannot be thought of as discrete protons and neutrons (it is a collection of quarks).
There is also believed to be similar structure to electrons with both spin and orbital angular momentum. It is all a bit complex and something that is not fully understood. Both magnetic moments and quadrupole moments have to be determined experimentally. Quadrupole moments are notoriously inaccurate because of the difficulty in measuring them.
Thanks - it is small for nuclea, but large for this this tiny nucleus: e.g. if for 1/2-1/2 charge configuration it would need ~0.8 fm distance between them, while naively we have just one charge.
Indeed - my main question is why not try to get down to quarks: while we cannot get quadrupole for single charge (proton), thinking about deuteron as 6 quarks it becomes doable.
Generally, why not consider some shift of quarks in binding?
For deuteron-p/n scattering models they need these 3-body forces ( https://en.wikipedia.org/wiki/Three-body_force ) - for 3 nucleons with 3-body forces we could fit anything. Maybe going down to quarks we 2-body forces would be sufficient?
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