particle[1](particle) refers to the minimum that can exist in a free statematerialcomponent.The first particles discovered areatom, electronic andprotonIt was discovered in 1932neutronIt is confirmed that atoms are composed of electrons, protons and neutrons, which are more basic material components than atoms, so they are called elementary particles.In the future, more and more such particles have been found, with a cumulative number of more than hundreds, and there is a growing trend;In addition, some of these particlesexperimentIt has not been found that it has an internal structure, and some particle experiments show that it has an obvious internal structure.It seems that these particles do not belong to the same level, so the term "elementary particles" has become history and is now collectively referred to as particles.Particles are not actual concrete substances such as neutrons and protons, but their general name, which is a model concept.The entry details particles such as electrons, atomic nuclei, mesons, quarks, leptons, and hadrons.
Chinese name
particle
Foreign name
particle
Alias
Elementary particle
Definition
It refers to the basic components of all material entities
Thomson discovered the electron in 1897, and Rutherford proposed the nuclear structure of the atom in 1911.Then we found photons and thought that "photons, electrons, protons and neutrons" were indivisible particles of matter, so we called them "elementary particles"[2]”。
At the end of the 19th century, it was believed that atoms were the smallest particles of matter.After the discovery of electrons, protons and neutrons, many people believe that photons and them are the "basic particles" of matter.
Hundreds of new particles not composed of protons, neutrons and electrons were gradually discovered;It is also found that protons and neutrons have their own complex structures.Since the second half of the 20th century, the word "basic" has been removed and collectively referred to as particles.
Since the 1930s, some new particles have been found in the study of cosmic rays.
The positron was discovered in 1932;
Muons were discovered in 1937;
In 1947, he discovered K meson and meson;
Later, some particles, called hyperons, whose mass is greater than that of protons, were discovered.
Encyclopedia x Knowledgeable: Illustration of Particles
Interactions between particles
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All particle structures of substances currently known
There are interactions between particles[3], YesStrong interaction、electromagnetismInteractionWeak interactionandGravitational interactionThe gravitational interaction is very weak and can be ignored.Through these interactions, new particles are generated or particle transformation phenomena such as particle decay occur.The particles are divided into the following categories according to the nature of the interaction: ① gauge particles.It refers to the medium particles that transmit interaction, and the particles that have been found to transmit electromagnetic effectphotonAnd deliveryWeak actionW, Z particles. ②Lepton。Not directly involvedStrong actionParticles that can directly participate in electromagnetic and weak interactions, including electrons, muons, tauons and associated electronsneutrinove、Muon neutrino、Tau neutrinoAnd their antiparticles. ③hadron。Particles that directly participate in strong interaction, electromagnetic interaction and weak interaction.amongspinbyintegerThe hadrons of are calledmeson, spin isSemiintegerThe hadrons of are calledbaryon。There are many hadrons, most of which are particles decayed by strong action. They have very short life and are unstable particles, also known asResonance state。
nature
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PVC particles
Each particle has its own intrinsic properties[2], mass with particles m（Static mass, expressed in energy), life τ (average life, refers to the average life of the stationary system), charge Q (in charge of the proton), spin J (in unit)ParityP、isospinI、Isospin 3rd component I3Baryon numberB、Lepton numberLe、、Lr、Singular numberS、Charm numberC 、base numberD and so on.
Under the accuracy of the existing experiments, leptons behave like point particles, without showing an internal structure, while hadrons show a composite particle with a certain structure.According to modern particle physics, a meson consists of a pair of positive and negative particlesquarkBaryons are composed of three quarks, and leptons and quarks belong to the same level.
Classification of particles
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More than 400 particles have been found.
According to the different relations between particles and various interactions, particles are divided into[2]：
Meson
Photons (transfer electromagnetic interaction)
Gluon (transfer strong interaction)
Lepton
Electronics
Electron neutrino
Muons and muon neutrinos
Tau and tau neutrinos
hadron
proton
neutron
meson
Hyperon
quark
Upper quark
Lower quark
Odd quark
Charm quark
Bottom quark
Top quark
Elementary particle
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Basic particles are the basic components of all material entities;Also refers toQuantum TheoryA particle with a fundamental force in it.
Strictly speaking, elementary particles are particles that can no longer be decomposed into any components.Under this definition, onlyquarkAnd leptons.But although protons andneutronComposed of quarks, these two types of baryons cannot be decomposed into their quark components, because independent quarks cannot exist.Therefore, although protons, neutrons and other baryons are composed of quarks, they are often regarded as elementary particles.
Electronic discovery
Until the end of the 19th century,atomIt has always been considered as the basic building block of matter.Later, BritainParticle physicsPioneersCavendish Laboratories, CambridgeOfJoseph John Thomson (Joseph John Thomson, 1856-1944), found that a kind of radiation produced by atoms can be explained by the flow of charged particles split by atoms themselves, and knew that such charged particles were electrons[4]。
Nucleus
Nuclear structure
Since the electron is negatively charged[5]The atom is electrically neutral. Obviously, there must be another positively charged particle inside the atom to offset the negative charge of the electron.In the early 20th century, Ernest Rutherford, a New Zealand born physicist working in Manchester (1871-1937) (laterThomson letCavendish LabDirector) proved that this positive charge, together with most of the atomic mass, is concentrated in a very small central nucleus.
At first it was thought that the nucleus was a mixture of electrons and positively charged protons.In 1932, he also worked in Cavendish LaboratoryJames Chatwick(James Chadwick, 1891-1937) discovered that the uncharged mass is almost the same as that of the protonneutron。thereforeNucleusA collection of protons and neutrons that is interpreted as being held together by strong nuclear interactions, or forces.
At that time, these three kinds of particles - electronprotonAnd neutrons
——It seems that there are only elementary particles constituting all substances, butcosmic raysResearch and particlesacceleratorMedium high energyParticle beamThe experiments of bombarding each other show that there are other types‘Subatomic’Particles;However, these 'new' particles are unstable. They will quickly 'decay' into showers of other particles, ending with familiar electrons, protons and neutrons.
It is important to understand that these new particles do not exist inParticle acceleratorThe 'interior' of particles (such as protons) bombarding each other in;They are derived from the energy injected into the accelerator according to Albert`Einstein(or, in the case under discussion, it is more appropriate).
However, during their short lifetime, they are real particles with characteristics such as mass and charge.Such particles should have appeared in large numbers under the high-energy conditions of the Big Bang.
meson
Physicists do not know how to incorporate these particles into a complete physical theory. They try to explain how the fundamental forces between these particles act.In doing so, they emulated the way photons carry charged particlesElectromagnetic forceWe want to use another kind of particle, meson, which carries force.But what are mesons made of?
quark
Quark composition
In 1964, physicist Gelman put forward the quark model, thinking that hadrons are composed of more basic components, which are called quarks.The quark model has been accepted by most physicists after decades of development[6]。
For a time, the situation was extremely chaotic.But in the 1960s and 1970sQuark theoryMake the situation clear.Quark theory holds that all known particles can be divided into two families.A family consists of quarks, which can 'sense' the strength that only works between quarks, called hadrons.The other group is called leptons. They cannot sense the power, but they participate in the so-calledweak forceIntermediary interactions (or weak interactions), such as radioactive decay (includingBeta decay）The process is caused by weak interaction.hadronIt can not only participate in strong interactions, but also sense weak forces.
Lepton
Lepton
They are really elementary particles, and they are not composed of anything else.canonical LeptonIt is the electron. The electron and another kind of neutrino (strictly speaking, it should beElectron neutrino）Leptons are associated with each other.When electrons participate in such processes as radioactive decay, neutrinos are always involved.
For some unknown reasons, this basic image has been copied twice, producing three generations of leptons.In addition to the electrons themselves, there are also heavier ones calledMesonThey are completely like electrons except that they are 207 times heavier than electrons;Another even heavier particle is called tau particle, whose mass is nearly twice that of proton.These two heavy electrons each have their own neutrinos, so there are six (three pairs) of particles in the lepton family.Although both muons and tau particles can be produced with energy in particle accelerators or fromcosmic rayBut they decay quickly and turn into electrons or neutrinos.
Hadron family
The hadron family itself is divided into two categories[7]。The particles composed of three quarks are called baryons, which are often called "matter" particles, including protons and neutrons (both baryons and leptons areFermionFermion is actually another name for ordinary matter particle.Particles composed of pairs of quarks are called mesons, and they carryFundamental forceAlthough there are other mesons (the carriers of these forces and other mesons are also calledBoson)。
Only two kinds of quarks are needed (their names are very strange, called 'Shang'quarkAnd 'lower' quarks) can explain the structure of protons and neutrons.Two protons held together by forceUpper quarkAnd aLower quarkConstitute, and oneneutronIt consists of two lower quarks and one upper quark held together by force.
The force itself can be regarded asGluonThe gluon itself is composed of quark pairs, so it is a meson.
Just as leptons reproduce for three generations, so do quarks.Although only two kinds of quarks are needed to explain the essence of protons and neutrons, the copied two generations of quarks are heavier than one generation. One generation is called 'odd' quark and 'charm' quark, and the heaviest generation is called 'bottom' quark and 'top' quark.andHeavy leptonSimilarly, these particles can be generated in high-energy experiments (so they must have existed in large numbers during the Big Bang), but quickly decay into their lighter counterparts.Although it is impossible to separate a single quark, particle accelerator experiments have provided direct evidence for the existence of all six members of the quark family;The last (top) quark was discovered in 2007 by scientists at the Fermi Laboratory in Chicago.
Studies on the mass and other properties of quarks show that there can be no more generations of quarks, only three groups of quarks and three groups of leptons.Fortunately, the standardBig Bang ModelIt is also believed that there can be no more than three generations of particles;Otherwise, the extra neutrinos in the very early universepressureIt should drive the universe to expand too fast, so that the remaining helium content is extremely oldfixed starThe observation results of are inconsistent (seeα β γ theory、Nucleosynthesis)。This is one of the most wonderful evidences, showing that both particle physics and cosmologyStandard modelThe description of the behavior of the universe is not far from the basic truth.
However, except for the first moment of the Big Bang, the second and third generation particles have little effect on the evolution of the universe or the behavior of its contents.Everything we see in the universe can be explained by two kinds of quarks (upper and lower) and two kinds of leptons (electrons and electron neutrinos);Indeed, since a single quark cannot exist independently, everything we see can still use the electrons, neutrons and protons known in 1932 plus electron neutrinos, andFour basic forces, which is fairly accurate.
University of CambridgeRecently, a press release said that researchers from the university and colleagues from Birmingham University had completed the research in cooperation.According to the bulletin, electronics are generally considered indivisible.But in 1981, some physicists proposed that under certain special conditions, electrons can be split into magneticspinon And chargedCaviton。
Cambridge University researchers placed the extremely thin "quantum metal wire" on a metal plate, controlled the distance between them to be about 30 atoms wide, and placed them in an ultra-low temperature environment of about minus 273 degrees Celsius, then changed the externalmagnetic field, found that the electrons on the metal plate are passing throughQuantum tunnelling effect When jumping onto the wire, it splits into autogyrons and hollow holes[8]。
Researchers say that people's research on electronic properties has set off a semiconductor revolution, which has led to the rapid development of the computer industry. There are also opportunities to actually study the properties of autospinons and holes, which may promote the development of the next generation of quantum computers and bring about a new round of computer revolution.[3]
Discover new particles
Fermi National Accelerator Laboratory
Sohu Science News on March 27, 2009[3]According to National Geographic, scientists announced this week thatFermi National Accelerator Laboratory A strange new particle has been found in, which can not be explained by the existing theory. It will probably break all the known rules for the composition of existing substances.This newly discovered particle is called Y (4140), which does not conform to the known pattern of two substances. Even scientists have not yet determined what Y (4140) is composed of.
Scientists have always believed that quarks can combine together to form other large subatomic particles in various effective ways. One mode is meson formed by quark anti quark pairs, and the other mode is baryon composed of three quarks, such as protons and neutrons."But this new particle we found does not belong to these quark combinations, which is surprising," said Jacob Koenigsberg of the University of Florida in the United States. "As far as we know, if you try to combine quark anti quark pairs together, you cannot build this particle."
Particle physicists said that the Y (4140) particle discovered this time was one of the members of the particle family with similar unconventional properties observed in these laboratories. It was generated by two beams of particles colliding violently with each other at the speed of near light speed, so the probability of discovering new particle Y (4140) was about 20 in 10 billion.The scientists in Fermilab found that the Y (4140) particle often produces a particle containing a bottom quark (called B+meson) in the process of decay.After screening trillions of proton and antiproton collisions in Fermilab, scientists determined a small sample of B+mesons decaying in an unconventional way.Further analysis shows that these B+mesons can decay into Y (4140).In addition, scientists also found that the Y (4140) particle can decay into a pair of other particles - J/psi and phi particles, which physicists believe may be a combination of charm and anti charm quarks.However, for such a composition, its decay characteristics are against the convention.
Seiji Yamauchi, a physicist and spokesman of the Japanese High Energy Laboratory, said that this was the first time to confirm that a new unexpected Y state new particle could decay into J/psi and phi particles.This Y state may be related to the Y (3940) they found earlier, or it may be another example of an exotic hadron containing charm quarks.These exotic quark combinations do not belong to known mesons and baryons,Theoretical physicistTheir real properties are being cracked, and the experimenters are also continuing to strive to find more such particles.
The discovery of this new particle challenges particle physicists who are familiar with how quarks combine to form matter.In addition, the United States announced the discovery of a rare single topped quark and several other discoveries, physicists actually missedHiggs boson(The so-called God particle) is getting closer, but now they have to rethink how matter is composed.This research result was published in the latest issue of Physical Review Letters.
epilogue
But there are probably more things in the universe than we can see;Both observation and theory have reasons to believe thatdark substanceMuch more than bright matter.A large part of dark matter may be particles that are neither hadrons nor leptons.But this is another topic.
