I need to work on my analogies. I've been using that phrase for months, trust HN to point out the error! To be fair, I base the analogy on the following:

Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can only be found within hadrons

"Rarer than a free quark" would save your analogy.

Rarer than a magnetic monopole would also work, but doesn't quite have the same ring.

Yes, but hadrons basically make up a lot of matter :-)

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

What? Bosons, such as a photon, definitely exist in the sense that they are part of the Standard Model of particle physics. They are as 'real' as electrons or quarks or, in some sense, a table.

My mistake, it's not something I've been following closely - I was under the impression there was debate re: their existence.

Higgs boson! Jeez! :-)

That may work this year, but I wouldn't bet on using that too long in 2012.