You want free quark, or if you want obscure-physics cred, you could say 'rarer than an odderon'. The (non?)existence of odderons has been an argument in particle physics for about 30 years...
http://en.wikipedia.org/wiki/Odderon
You want free quark, or if you want obscure-physics cred, you could say 'rarer than an odderon'. The (non?)existence of odderons has been an argument in particle physics for about 30 years...
http://en.wikipedia.org/wiki/Odderon