Atoms are composed of neutrons, protons, and electrons. Neutrons and protons seem to be composed of quarks. What else is there below? What is the smallest particle?

In quantum field theory, there are three types of fields and 62 types of particles. The first physical particle field includes 48 types of particles, including leptons and quarks. An electron is a lepton. Although it seems that quarks cannot be divided anymore, there is a subtle correspondence between leptons and quarks. People divide them into three generations:

First generation: up quark and down quark

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Two: Strange quarks and charm quarks

Three: Top quarks and bottom quarks

Leptons also include electrons, neutrinos, etc.

Among all the 62 particles, the lepton type particles are the smallest.

Quark

quark

In the 1960s, American physicists Murray Gell-Mann and G. Zweig independently proposed the neutron Hadrons such as protons and protons are composed of more basic units - quarks, which many Chinese physicists call "stratons". They have a fractional charge, which is 2/3 or -1/3 times the charge of an electron, and have a spin of 1/2. The word quark was taken by Gell-Mann from J. Joyce's novel "Finnegan's Sleepover" The phrase "The king of reviewers for Mark, the three-tone quark". Quark has many meanings in the book, one of which is the sound of a seabird. He believed that this was suitable for his original peculiar idea that "elementary particles are not basic and basic charges are not integers." At the same time, he also pointed out that this was just a joke, which was a rebellion against the pretentious scientific language. In addition, it may also be the reason why he likes birds.

The original theory to explain strongly interacting particles required three kinds of quarks, called the three flavors of quarks. They are up quark (up,u), down quark (down,d) and strange quark (strange). ,s). The J/ψ particle was discovered in 1974, requiring the introduction of the fourth quark, charm quark (charm, c). The Y particle was discovered in 1977, requiring the introduction of the fifth quark, bottom quark (bottom, b). The sixth quark, the top quark (top, t), was discovered in 1994 and is believed to be the last quark.

Quark theory holds that all baryons are composed of three quarks, and antibaryons are composed of three corresponding antiquarks. For example, proton (uud), neutron (udd). Quark theory also predicts the existence of a particle (sss) composed of three strange quarks. This particle was observed in a hydrogen bubble chamber in 1964 and is called a 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)

u up quark up +2/3 0.004

d down quark down -1/3 0.008

c charm quark charm +2/3 1.5

< p>s strange quark strange -1/3 0.15

t top quark top +2/3 176

b bottom quark bottom -1/3 4.7

In quantum chromodynamics, in addition to the "flavor" properties, quarks also have three "color" properties, namely red, green and blue. "Color" here does not mean that quarks actually have color, but uses the word "color" to vividly describe a physical property of quarks themselves. Quantum chromodynamics believes that general matter has no "color". The "colors" of the three quarks that make up baryons are red, green and blue, so when superimposed together they become colorless. Therefore, including the attributes of 6 flavors and 3 colors, there are 18 kinds of quarks, and their corresponding 18 kinds of antiquarks.

Quark theory also believes that mesons are bound states composed of a quark and an anti-quark of the same color. For example, the [[π+ meson]] predicted by Japanese physicist Hideki Yukawa is composed of an up quark and an anti-down quark, and the π-meson is composed of an anti-up quark and a down quark. They are both Colorless.

Five kinds of quarks except the top quark have been discovered through experiments. The Chinese scientist Ting Zhaozhong won the Nobel Prize in Physics for the discovery of the charm quark. One of the main research directions of high-energy particle physicists in the past decade has been the top quark (t).

As for the sixth "top quark" newly discovered in 1994, it is believed to be the last one. Its discovery allows scientists to obtain a complete picture of quarks, which will help study the origin of the universe at the beginning of the Big Bang. How the universe evolved in less than a second because the initial intense heat from the Big Bang created top excitation particles.

Quark theory believes that quarks are trapped inside particles, and there are no individual quarks. Some people have objected, arguing that quarks are not real. However, almost all predictions made by quark theory agree well with experimental measurements, so most researchers believe that quark theory is correct.

Let me correct it: Some people say that a certain quark was discovered, which is completely fabricated without understanding science. Now humans are just making bold assumptions and scientific verification. Quarks were proposed to explain some phenomena that humans cannot explain at present. There may be hypotheses, but humans have never found direct evidence of the existence of quarks.

On December 2, 1996, "Science and Technology Daily" published Professor Cui Junda's refutation of Academician He Zuoma's article "The theory of composite space-time is not "Sick Science". Cui further pointed out in the article: "Not everyone in the physics community recognizes the existence of quarks. Different opinions have existed as early as the 1970s. Chinese physicist Zhu Hongyuan, Nobel Prize winner and founder of quantum mechanics Heidelberg all believe that: many people around the world Physicists have spent so much effort searching for quarks. If quarks really exist, they should have been found long ago. "

Of course it is wrong for this scientist to deny quarks, like the sentence "If quarks are real." "It should have been found long ago" is obviously a fallacy, which is equivalent to saying "if cancer really existed, it should have been cured long ago"

In short, science cannot be false or emotional, and quark cannot. Directly proving its existence cannot prove (even indirectly) its non-existence. It is currently just a hypothesis.