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Basic info
quarks exist only in groups
Color is just a metaphor.
QCD personalities
Rutherford-style scattering experiments showed a three part structure for the proton.
Murray Gell-Mann
In 1963, when I assigned the name "quark" to the fundamental constituents of the nucleon, I had the sound first, without the spelling, which could have been "kwork." Then, in one of my occasional perusals of Finnegans Wake, by James Joyce, I came across the word "quark" in the phrase "Three quarks for Muster Mark." Since "quark" (meaning, for one thing, the cry of a gull) was clearly intended to rhyme with "Mark," as well as "bark" and other such words, I had to find an excuse to pronounce it as "kwork." But the book represents the dreams of a publican named Humphrey Chimpden Earwicker. Words in the text are typically drawn from several sources at once, like the "portmanteau words" in Through the Looking Glass. From time to time, phrases occur in the book that are partially determined by calls for drinks at the bar. I argued, therefore, that perhaps one of the multiple sources of the cry "Three quarks for Muster Mark" might be "Three quarts for Mister Mark," in which case the pronunciation "kwork" would not be totally unjustified. In any case, the number three fitted perfectly the way quarks occur in nature.
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Timeline
- The first three quarks are hypothesized: up, down, and strange.
- Evidence for a fourth quark is found in November of 1974. Two experiments simultaneously announced the discovery of a meson with a mass of about 3.1 GeV/c2. Called the J meson by one group and the ψ meson by another it was later determined to be a combination of charm and anticharm quarks. Since neither group had priority on the discovery, the meson is now called J/ψ. Like many particles discovered in the Twentieth Century, it was also given a whimsical name: charmonium.
- Unexpected discovery of the bottom quark
- Mass of the top quark finally determined. The top quark is more massive than many atoms. and it is so unstable that is does not live long enough to combine with other quarks to form a hadron.
18 quarks
| red | green | blue | |
| up | √ | √ | √ |
| down | √ | √ | √ |
| strange | √ | √ | √ |
| charm | √ | √ | √ |
| top | √ | √ | √ |
| bottom | √ | √ | √ |
8 gluons
| green-antired | blue-antired | |
| red-antigreen | blue-antigreen | |
| red-antiblue | green-antiblue |
| (red-antired) − (green-antigreen) |
| √2 |
| (red-antired) + (green-antigreen) − 2(blue-antiblue) |
| √6 |