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Symmetry between up and down quarks is more broken than expected

(phys.org)
87 points terminalbraid | 1 comments | 29 Mar 25 10:12 UTC | HN request time: 0.208s | source
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ars ◴[31 Mar 25 15:54 UTC] No.43536434[source]▶
BTW isospin is actually how many up vs down quarks they are. It's not a fundamental property like spin or charge.

It's an old term that was created before they knew that up and down quarks existed.

Personally I find the term outdated because there are 4 other quarks, and isospin only talks about two of them.

replies(3): >>43537038 #>>43537436 #>>43538771 #
1. dudu24 ◴[31 Mar 25 19:24 UTC] No.43538771[source]▶
This misses the point of isospin. Isospin is an approximate SU(2) symmetry due to the fact that the up and down quarks (the "light" quarks) have very similar masses compared to the rest of the quarks, so they can be approximated as two different eigenstates of the same particle. It's mathematically identical to the SU(2) symmetry of a spin-half particle. The reason it doesn't include the other quarks is because they are so much more massive.