Back in the early Pleistocene, when WC was just a pup, stuff was made of protons, neutrons and electrons, collectively atoms. It didn’t get any smaller than that.
Along came Murray Gell-Mann and his crowd of physicists, who developed the Standard Model of physics, creating a whole new bestiary of subatomic particles. There’s dozens of the rascals, but WC is only going to tackle the ones called “quarks,” because there has been an important development in the science of quarks.1 WC apologizes in advance to any particle physicists who read this and are offended by the gross simplifications.
Stuff like protons and neutrons – the stuff of an atomic nucleus – is composed of quarks. Specifically, the kinds of quarks called “Up” and “Down.” A proton is composed of two Up quarks and one Down quark. A neutron consists of two Down quarks and one Up quark. The Standard Model allows six kinds of quarks, the purple colored boxes in the chart. In addition to the Up and Down, there are Strange, Charm, Top and Bottom.2 The mass of these quarks varies greatly, by several orders of magnitude. A Charm quark, for example, is about 600 times as massive as an Up quark. That great mass makes Strange, Charm, Top and Bottom quarks highly unstable in combination. So assembling atomic particles with the heftier quarks is problematic.3
So it’s a Big Deal that the physicists at CERN have discovered a new Baryon – a new triplet of quarks – consisting of two Charm quarks and one up quark. The standard model predicts the existence of such a particle and its properties. And the reality matched up pretty well with the prediction, another win for the Standard Model. The new Baryon is named Xi-cc++ (pronounced ka-sigh-see-see-plus-plus),4 weighs about 3.8 times as much as a proton, and decays very, very quickly, with a lifetime somewhere between 50 millionths of a billionth of a second and 1,000 millionths of a billionth of a second.5
Back in 2002, physicists discovered a close cousin to Xi-cc++, consisting of two Charm quarks and a Down quark (remember Xi-cc-++ consists of two Charms and an Up quark). Puzzlingly, the new particle is heavier and hangs around longer than it earlier-discovered cousin. So particle physicists have something new to argue and think about.
Quarks are unique among the Standard Model’s bestiary because they react to all four fundamental interactions of contemporary physics: electromagnetism, gravitation, strong interaction, and weak interaction. Those interactions are mediated by other kinds of particles, including the infamous Higgs Boson.
Does all of this stuff have any practical use? Any particle physicist would tell you that’s a silly question. Understanding how the universe is assembled is an end in itself. But consider that a minor implication of Einstein’s Special Law of Relativity gave us the global positioning system. You just never know.
UPDATE: Today’s XKCD comic is amusingly relevant to WC’s blog post. For the record, the blog post went up first…
- It was Murray Gell-Mann who named this particular particle zoo. He was reading James Joyce’s Finnegan’s Wake,, and came across the line ” — Three quarks for Muster Mark!” ↩
- The names are usually described as whimsical. Silly might be a better word. Terry Pratchett, at one time a press officer for the nuclear energy industry, has had great fun with them. ↩
- Strange, Charm, Top and Bottom quarks seem to have existed only in three specialized situations: (1) immediately after the Big Bang, when the universe was still a high energy soup; (2) in the collisions of certain kinds of high energy cosmic rays; and (3) in modern particle accelerators. ↩
- Which suggests that particle physicists have used up all of their alleged whimsy. If you don’t think so, read the paper announcing the discovery. ↩
- In a remarkable coincidence, that’s almost exactly the amount of time Donald Trump retained any measurable credibility as President of the United States. ↩