Hypercharge and Strangeness
DOI link for Hypercharge and Strangeness
Hypercharge and Strangeness book
Let’s now go back to the 1950s to the discovery of strange particles. By this time, isospin was well established as an approximate symmetry of the strong interactions, broken by the weak and electromagnetic interactions. Experimenters began to notice a strange new class of particles which were produced in pairs in scattering of strongly interacting particles, and decayed much more slowly back into ordinary particles. It was eventually realized that a lot of the physics could be understood if there were an additive quantum number, called strangeness that was conserved by the strong (and electromagnetic) interactions, but not by weak interactions. Call it S. Particles which carry a non-zero value of S are called strange particles.