I have seen only two arguments for the fact that composite particles, like protons, nuclei, or even Helium-4 atoms, are identical and can be considered bosons or fermions according to their total spin.(adsbygoogle = window.adsbygoogle || []).push({});

The first, in Feyman's lectures [third volume, 4-2]. It is said that if the composite particles are far apart and there is not an appreciable probability of exchanging any of the internal particles, we can consider them as simple objects. In a scattering experiment, either there is no exchange or all the internal particles are exchanged at the same time [why?]. So, for the four fermions of the alpha particle, interchanging them brings a plus sign and the particle is a boson.

The second, in many textbooks. It is reasoned that in the cases we consider the internal degrees of freedom are locked, since excitations require higher energy steps then provided by thermal energy. So the composite particle can be thought as a fundamental particle. Then you can apply the spin-statistics theorem.

Actually I don't understand both of these arguments, I find them too qualitative. I am asking if there is a better, quantitative, justification, that explains also the extent of the approximation.

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# Are composite particles, like atoms, identical bosons/fermions?

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