Anything with a substructure has excited states. Molecules, atoms, nuclei all can absorb photons which causes them to make a transition to an excited state. Conversely, when they jump from an excited state to a lower energy state, energy is emitted in the form of photons. Can proton and neutrons (having electrically charged quarks inside them) have such excited states?
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asked Feb 2, 2020 at 17:31
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$\begingroup$ This actually approved the quark model which existed before just as empirical prediction. $\endgroup$– sanarisCommented Feb 2, 2020 at 18:57
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1 Answer
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Yes, nucleons have excited states and resonances. The two middle delta baryons are the most well-known with spin 3/2 instead of 1/2 for the proton and neutron, followed by the Roper resonances. There is a fairly long list of such states by now, running up to 2700 MeV and 13/2 spin for nucleons.
answered Feb 2, 2020 at 19:56
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$\begingroup$ The answer is correct, but the "catch" is that these particles barely exist: their decay width is comparable to the excitation energy. The way a block of wood "kind of" has a pitch when you strike it. These particles manifest as small, round peaks in the scattering cross-section and not much else. We can do fun stuff with muons such as bubble chambers and spectra of muonic atoms. But we can't, for example, make an exotic carbon nucleus with a delta baryon and then measure it's charge radius. $\endgroup$ Commented Jan 3, 2023 at 9:16