The Mystery Of The Proton Spin

If you are not familiar with the issues surrounding the origin of the proton's spin quantum number, then this article might help.

It explains the reason why we don't believe that the proton spin is due just to the 3 quarks that make up the proton, and in the process, you get an idea how complicated things can be inside a proton.

There are three good reasons that these three components might not add up so simply.

1. The quarks aren't free, but are bound together inside a small structure: the proton. Confining an object can shift its spin, and all three quarks are very much confined.
2. There are gluons inside, and gluons spin, too. The gluon spin can effectively "screen" the quark spin over the span of the proton, reducing its effects.
3. And finally, there are quantum effects that delocalize the quarks, preventing them from being in exactly one place like particles and requiring a more wave-like analysis. These effects can also reduce or alter the proton's overall spin.

Expect the same with a neutron.

Zz.