What is the difference between $\Lambda$ and $\Sigma$ baryons? 
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*The Lambda (uds) - 1115 MeV

*The Sigma (uds) - 1192 MeV


Other than the 77 MeV,  why are these 2 different particles?  Is it the spin of 1 quark?  If so, is it possible to determine which one?  If not spin, what could it be?
 A: Looking at the Particle Data Group summaries, the $\Lambda $ bayrons have strong isospin $I=0$, which means that there is only one charge state.
The $\Sigma$ baryons, on the other hand, have $I=1$.
This means that all $\Lambda$ baryons are electrically neutral, while the $\Sigma$ (like the $\pi$ meson, which also has $I=1$) may have charge zero or $\pm1$.
For what it's worth, the names attached to these particles categorize them by their quantum numbers; the links above list dozens of particles classified as $\Lambda$ or $\Sigma$.
The lowest-mass $\Sigma^0$, which I assume you're referring to as "the Sigma," isn't heavy enough for the isospin-conserving decay $\Sigma^0\to\Lambda\pi$, and therefore decays via the isospin-changing channel $\Sigma^0\to\Lambda\gamma$.
However, the more massive $Σ(1385)$ may undergo the isospin-conserving decay, and therefore has a much briefer lifetime.
The lightest $\Lambda$ baryons, however, can't decay without undergoing a strangeness-changing weak interaction, so the decay of the lightest $\Lambda^0$ is $10^{10}$ times slower than the decay of the lightest $\Sigma^0$.
A: "[Sigma baryons] are closely related to the Lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange."
https://en.wikipedia.org/wiki/Sigma_baryon
