What is quark?

A proton and an antiproton collide at high energy, producing a pair of almost free 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 fundamental 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.

What is quark?

1, a particle with no more than three quarks.

2. All baryons are composed of three quarks, while anti-baryons are composed of three corresponding antiquarks, such as protons and neutrons. Proton consists of two upper quarks and one lower quark, and neutron consists of two lower quarks and one upper quark.

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They have a fractional charge, which is 2/3 or-1/3 times of the electron charge, and their spin is 1/2. 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 proton (uud) and neutron (UDD). Antibaryons consist of three corresponding antiquarks. 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. Top quarks, bottom quarks, odd quarks and charm quarks will decay into upper quarks or lower quarks in a short time due to their huge mass (see the table below). Quarks are divided into three generations according to their characteristics, as shown in the following table:

Charge quantity of Chinese and English name symbols in substitution function /e mass /MeV.c-2

Quarks on1+1/2iz =+1/2u+2/31.5 to 4.0.

1 ? 1/2 Iz=？ 1/2 quark) d? 1/3 4 to 8

2 ? 1/2 S=？ 1 strange quark) s? 1/3 80 to 130

2+ 1/2 C= 1 charm quark C+2/3 1 150 to 1350.

3 ? 1/2 B′=？ 1 bottom quark) b? 1/3 4 100 to 4400

3+ 1/2 T= 1 top quark t+2/3171400 2100.

Antibaryons consist 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.

Some physicists in our country call quarks straton, because they think that even straton is not the initial element of matter, but only one layer in the infinite layer of matter structure.

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.

Five kinds of quarks except the top quark were discovered through experiments. Ding Zhaozhong, a scientist from China, won the Nobel Prize in physics for discovering charm quarks (also known as J particles). Top quark (T) is a main direction of high-energy particle physicists in recent ten years.

As for the sixth "top quark" newly discovered by 1994, I believe it is the last one. Its discovery enables scientists to obtain a complete picture of quarks, which helps to study how the universe evolved in less than a second at the beginning of the Big Bang, because the high heat generated at the beginning of the Big Bang will produce top quark particles.

Studies have shown that some stars may become "quarks" at the end of evolution. When a star cannot resist its gravitational contraction, quarks will be squeezed out by a large increase in density. Eventually, a star the size of the sun may shrink to only seven or eight kilometers, but it will still shine.

Quark theory holds that quarks are all trapped inside particles and there is no single quark. Some people object that quarks do not really exist. However, almost all the predictions made by quark theory are in good agreement with the experimental measurements, so most researchers think that quark theory is correct.

1997, Russian physicist Diane Konov and others predicted that there was a particle composed of five quarks, the mass of which was 50% greater than that of hydrogen atom. In 200 1 year, Japanese physicists discovered the evidence of the existence of pentaquark particles when they bombarded a piece of plastic with gamma rays on the SP Ring-8 accelerator. It was later confirmed by physicists at Thomas Jepperson National Accelerator Laboratory and Moscow Institute of Theoretical and Experimental Physics. This pentaquark particle consists of two upper quarks, two lower quarks and an anti-singular quark, which does not violate the standard model of particle physics. This is the first time that a particle composed of more than three quarks has been found. Researchers believe that this particle may be only the first member of the "five quarks" particle family to be discovered, and there may be particles composed of four or six quarks.

One by one, nine experimental groups claimed to have found evidence of five quarks. But in other high-energy experimental groups and their data, including the use of lepton colliders, such as Zeus experiment in DESY, Germany, Belle in KEK, Japan and BaBar in SLAC, USA, as well as CDF and D? In the experiment, no evidence that should exist was observed. Therefore, the existence of the so-called five quark particles is still a controversial topic. At the same time, Chun8 also plans to further improve the efficiency, and the radiation is 10 times stronger than the current one, so as to obtain more experimental data for statistical confirmation.

At present, human beings are only making bold assumptions and scientific verification. Quark is a possible hypothesis to explain some phenomena that cannot be explained by human beings at present, but human beings have never found direct evidence of quark.

199665438+On February 2nd, Science and Technology Daily published Professor Cui Junda's article "Composite Space-time Theory is not Pathological Science". Cui further pointed out in the article: "The existence of quarks is not universally recognized in physics. The differences can be traced back to the 1970s. Zhu Hongyuan, a physicist in China, and Heidelberg, the founder of quantum mechanics, all think that many physicists all over the world have spent so much effort to find quarks. If quarks really existed, they should have been discovered long ago.

It is certainly wrong for this scientist to deny quarks, just like the sentence "If quarks really existed, they should have been discovered 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 anything false and emotional. Quarks cannot directly prove its existence, nor can they prove (even indirectly) that it does not exist. At present, it is only a hypothesis.