Quantum Chromodynamics

Discussion

disorganized notes

Basic info

quarks exist only in groups

• mesons: bound quark-antiquark pair
• hadrons: quark triplets
• pentaquark: four quarks and an antiquark (Physical Review Letters, 4 July 2003) formed by the coalescence of a neutron (udd) and a K⁺ meson (u-s)

Color is just a metaphor.

QCD personalities

• Murray Gell-Mann (1929–0000) USA
• George Zweig (1937–0000) USA
• Oscar Greenberg (????–0000) USA
• Yoichiro Nambu (1921–0000) Japan
• Yuval Ne'eman (1925–2006)

Rutherford-style scattering experiments showed a three part structure for the proton.

http://www.nobel.se/physics/laureates/1990/press.html

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.

Murray Gell-Mann

James Joyce. Finnegan's Wake. Book 2, Episode 4, Page 383

Three quarks for Muster Mark!
Sure he hasn't got much of a bark
And sure any he has it's all beside the mark.
But O, Wreneagle Almighty, wouldn't un be a sky of a lark
To see that old buzzard whooping about for uns shirt in the dark
And he hunting round for uns speckled trousers around by Palmerstown Park?
Hohohoho, moulty Mark!
You're the rummest old rooster ever flopped out of a Noah's ark
And you think you're cock of the wark.
Fowls, up! Tristy's the spry young spark
That'll tread her and wed her and bed her and red her
Without ever winking the tail of a feather
And that's how that chap's going to make his money and mark!

James Joyce

Timeline

1964. The first three quarks are hypothesized: up, down, and strange.
1967. Richard Taylor, Jerome Friedman, and Henry Kendall used Stanford University's linear electron accelerator to probe this fuzzball by shooting electrons at protons. Some of the electrons scattered quite strongly, revealing that the proton was not simply a uniform smear of matter. Later that year, theoretical analysis by James Bjorken suggested that this scattering could result from point-like constituents within the proton
1974. 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.
1977. Unexpected discovery of the bottom quark
1995. 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

8 gluons

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