Dumb sort of basic question

From: Richard Schultz (schultr_at_mail.biu.ack.il)
Date: 07/11/04 

Date: Sun, 11 Jul 2004 14:23:32 +0000 (UTC)

Could someone remind me why a meson must necessarily be a quark and an
anti-quark rather than two of one or the other? I assume that there is
some fundamental symmetry that requires it (and I have a sneaking
suspicion that someone has already explained it to me, although I couldn't
find it in a cursory Google search), but which one is not clear to me.
Similarly, does a baryon have to be three quarks or three anti-quarks?

I realize that empirically, no such particles have been observed (they'd
have fractional charges), but it's not clear to me what fundamental rule
prevents particles from having fractional charges.

TIA. . .

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Richard Schultz schultr@mail.biu.ac.il
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Opinions expressed are mine alone, and not those of Bar-Ilan University
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"Logic is a wreath of pretty flowers which smell bad."

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