The Standard Model: Part 1- Quarks and Leptons

Chances are, if you've seen a science program about physics in the last five to ten years, the narrator or host mentioned the Standard Model. The Standard Model is just that: it's the most commonly used (standard) mathematical description of the universe (model) for high energy physics at the moment. It's also relatively recent. The oldest parts of the model (electrons) date back to the late 1800's, while some of the details (neutrinos, the Higg's Boson) are still being debated today. After the jump, I'm talking about some of the particles found in the Standard Model.

So, matter is subdivided between two fundamental camps: that which is fermionic, or has half-integer spin (see here for a description of spin), and that which is bosonic, or has integer spin. Today, we're talking about the fermions.
The basic fermions are the quarks and the leptons. As you can see in the aboce diagram, both the quarks and the leptons come in three sets (generations) of pairs. For the quarks, this is the up and down quarks, the charm and strange quarks, and the top and bottom quarks. For leptons, this is the electron and electron neutrino, the muon and the muon neutrino, and the tau lepton and tau neutrino. Much like the periodic table, there are some patterns in the table of particles. Reading the quarks and leptons left to right, we go from lightest to heaviest. The top row of quarks all have +2/3 eletric charge, while the bottom row of quarks all have -1/3 electric charge. The electron, the muon, and the tau lepton all have -1 electric charge, and the neutrinos all have zero charge.
But what does it all matter? For one, conservation laws must be maintained. Remember, the net number of quarks and leptons in an interaction must be conserved, as must the net charge of the system. Also, the type of particle tells us what interactions it can participate in. If it has mass, it can interact through gravity. If it has charge, it can interact electromagnetically. If it's a quark, it has a different form of charge (color charge), and can interact via the strong force. If it's a fermion (quarks, leptons, and some other stuff), it can interact via the weak interaction. That's why neutrinos are so interesting for physicists: they have no charge (no electromagnetic force), no color charge (no strong force), and nearly no mass (can pretty much ignore gravity), so they don't interact much. In fact, they can only interact via the two weakest forces: gravity and the weak force. This makes them incredibly hard to detect, making neutrinos a fairly unknown variable that (if we could measure it better) could distinguish between lots of models.
Tomorrow, let's talk forces. We've been throwing around the names a lot, but we really haven't described them. We'll try to correct that tomorrow.