Actually, it is a "Higgs-like particle" with the weight of a Barium atom, previously being innert since it only has mass but does not interact otherwise with our physical and chemical world. Predicted is that 2/3 of all gravity in the universe consists of higgs-like matter. Quarks are way smaller hand are observed when matter decays because some funny physicists put stuff (protons, neutrons, or whatever) in a tube and accellerate it so they they can see it go boom with something going the other way.
Edit: I realized that wasn't clear: Why "Higgs-like particle?" because they measured different sizes and it could be indeed a whole set of new kind of matter they started to discover. It's very exciting and me as an interrested N00b in the field of Physics, I like to read more about such stuff.