What are quarks and what are the various types of quarks? Well, that’s an excellent question. Well the story goes back to the old days, the very old days, when people thought that objects were what they saw. They could measure their mass or volume and that was it. Then, there came Democritus, an Ancient Greek philosopher, and keep in mind that there is always a Greek guy trying to spice things up and formulate an atomic theory for the universe. Democritus in this case proposed that matter consists of small particles that he called atoms. Atom, was till the days of Rutherford in 1911 the smallest particle of matter. With his experiments Rutherford discovered that an atom consists of electrons, protons and neutrons. Once again, the scientific community could sleep blissfully thinking the mystery of matter was solved once and for all. Things chanced in 1964, when Murray Gell-Mann had a different view. He proposed, and his theory was experimentally confirmed in the following years, that protons and nucleons where in fact ‘too big’ to be the fundamental constituents of matter.
It was he who introduced the world to the first three types of quarks. He chose the name ‘quarks’, a word used by James Joyce in the novel Finnegan’s Wake:
‘Three quarks for Muster Mark!’
How many types of quarks are they really? There are 6 different types or flavours as they are called, big surprise if you ask me. Each type has a fractional electric charge, +2/3 or -1/3, unlike proton and electron which have charges +1 and -1 respectively. Each one also has an extra type of charge called colour charge: red, green and blue. You think you know enough? We just got started! For each one of these types of quarks there is a corresponding antiquark, which has the opposite charge, -2/3 or +1/3, and the complementary colour of its alter ego: antired, antigreen and antiblue.
Do these types of quarks have a unique name? They sure do! Up quark (u), down quark (d), charm quark (c), strange quark (s), top or truth quark (t) and bottom or beauty quark (b). Pretty cool, huh? Usually, the scientists refer to them as pairs: up-down, charm-strange and top-bottom. Up, charm and top quarks have a +2/3 charge while down, strange and bottom quarks have a – 1/3 charge. At this point, we should emphasize that quarks cannot ‘live a single life’ and always hang out with each other. According to their mass, up and down are the lightest ones and top is the most massive one. Gell-Mann had only discovered the first three types of quarks up, down and strange. The top quark was the one that was discovered last in 1995.
So how is matter organized? Well, experiments so far propose the following: An atom consists of a nuclear and electrons ‘traveling around’ it. The nuclear consist of protons and neutrons. Protons and neutrons consist of various types of quarks. For example, a proton consists of two up and one down quark thus its charge is +1 (+ 2/3 + 2/3 – 1/3 = +1).
Confussed? If so, just go to the supermarket and buy 500g of quark, the dairy product of course, and cook a delicious lemon cheesecake. Just be careful