Isospin

Quantum number related to the weak interaction

In nuclear physics and particle physics, isospin ( I) is a quantum number related to the up- and down quark content of the particle. Isospin is also known as isobaric spin or isotopic spin. Isospin symmetry is a subset of the flavour symmetry seen more broadly in the interactions of baryons and mesons.

From Wikipedia, under CC BY-SA. More on occurri.