How big are quarks?

1964, American physicists Murray gherman and G Zweig independently proposed that hadrons such as neutrons and protons are composed of quarks, a more basic unit. They have fractional charge, which is 2/3 times that of elementary charge or-1/3 times, and their spin is 1/2. The word quark is taken from James Joyce's novel A Night Sacrifice in finnigan, written by gherman. This is the "set mark of three quarks". Quarks have many meanings in this book, one of which is the sound of seabirds. He thinks this is suitable for his original strange idea that "elementary particles are not basic and elementary charge is not an integer", and he also points out that this is just a joke and a resistance to pretentious scientific language. In addition, it may be because of his love for birds.

First of all, three kinds of quarks are needed to explain the strong interaction particle theory, which is called quark three flavors. They are upper quark (up, u), lower quark (down, d) and singular s quark (s). 1974 The discovery of the J/ψ particle requires the introduction of the fourth quark charm quark (Charm, C). The particle υ was found in 1977, which requires the introduction of the fifth quark bottom (b). The sixth quark top, T quark (T), was found in 1994 and is considered as the last quark.

Quark theory holds that all baryons are composed of three quarks, while anti-baryons are composed of three corresponding antiquarks. Such as protons (uud) and neutrons (udd). Quark theory also predicted the existence of a particle (sss) composed of three strange quarks, which was observed in the hydrogen bubble chamber of 1964 and was called negative ω particle.

Quarks are divided into three generations according to their characteristics, as shown in the following table:

Symbol Chinese name English name Charge (E) Mass (GeV/C 2)

Quark up +2/3 0.004 on U

D under quark-1/3 0.008

C charm quark charm +2/3 1.5

S strange quark monster-1/3 0. 15

T-top quark top +2/3 176

B quark bottom-1/3 4.7

In quantum chromodynamics, quarks not only have the characteristics of "taste", but also have three characteristics of "color", namely, red, green and blue. Here, "color" does not mean that quarks really have color, but uses the word "color" to vividly compare a physical property of quarks themselves. Quantum chromodynamics holds that general matter has no "color", and the "colors" of the three quarks that make up baryons are red, green and blue respectively, so they are colorless when superimposed together. So it includes six flavors and three colors, * * * has 18 quarks and their corresponding 18 antiquarks.

Quark theory also holds that mesons are bound states composed of a quark and an antiquark of the same color. For example, Japanese physicist Hideki Yukawa predicted that [[π+meson]] consists of an upper quark and an anti-lower quark, while π-meson consists of an anti-upper quark and a lower quark, which are colorless.