MadSci Network: Physics

Re: Why are there 8 gluons?

Date: Mon Apr 2 21:48:05 2001
Posted By: Benn Tannenbaum, Post-doc/Fellow, Physics and Astronomy, University of California, Los Angeles
Area of science: Physics
ID: 985484939.Ph

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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