|MadSci Network: Physics|
Hi Girish, I apologize for the delay in answering your question. Your first question is rather technical! I refer to "Introduction to Elementary Particles" by David Griffiths for my answer. It has to do with the fact that gluons, like all elementary particles, can be classified according to "groups", a mathematical concept in group theory. As it happens, the group which is used to classify gluons is SU(3). It doesn't allow for states like (y, ybar) as you mentioned, but instead such horrid things like (r,bluebar + blue, redbar)/sqrt(2)! There is, by definition, a state that is (r,redbar + blue,bluebar + green,greenbar)/sqrt(3), but that would allow a "free" gluon. Since we never see these gluons, they don't exist in our world. I've over simplified, I'm afraid, but your question requires about 2 years of graduate work to really understand! The second question is also tough! I have done some digging and the best that I can do is this: the electron was the original elementary particle. Its name may come from "electric one". The next one named was the proton, from the Greek meaning "heavy". The rest follow from that! I hope this helps!
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