Strange particle, that is, allSingular numberNonzeroparticle。TheirpeculiarThe nature is to produce together, produce fast and decay slowly.At first, it could not be explained, so it was called strange particle.[1]
1953 MGelmanWest Island introduces newQuantum numberSingular number successfully explains thisstrangenature.
In 1947cosmic raysIn the research of, strange particles were first observed, but only in 1954acceleratorAfter the strange particles were produced in the experiment, the "strange" characteristics of such particles were gradually clarified through systematic research.The so-called strange particles refer to a large number of newly discovered particlesNew particle。
In 1947, when p-mesons were discovered, people took two pictures with V-shaped tracks in the cloud chamber using cosmic rays. The decay products were p ± mesons and protons (p).These two kinds of tracks cannot be explained by any first generation particles found at that time, so people naturally thought that they must be formed by the decay of two undiscovered particles.In the following years, people took more than 100000 cosmic ray pictures and finally discovered these two new uncharged particles.One of them is 1000 times the mass of the electron and is called "k0 meson";The other is about 2200 times of the electronic mass, called the l particle (read "Lamberta").We call them the second generation particles because they have two obvious characteristics: (1) fast production and slow decay;(2) Paired (synergetic) production, single decay.These characteristics cannot be explained by past theories, so they are also called "strange particles".
In order to quantitatively study these strange particles, it is not enough to rely on cosmic rays alone.In the early 1950s, some large accelerators were built one after another, making it possible for people to use the particles accelerated by the accelerator to bombard the atomic nucleus to study exotic particles.
By 1964, people had discovered a batch of strange particles, making the number of particle types discovered reach 33.These strange particles are collectively called "second generation particles".Excerpted from quantum mechanics book "Seeing the Little and Knowing the Little"[2]
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The characteristic is that when they are produced due to the collision between particles, they are always produced together, and they are produced very quickly, but the decay acts independently and decays slowly.To put it simply, they are always co generated and non co decayed.In 1953, Gelman used a newquantumNumber, namely odd number, is used to express this property, and it is assumed that the singular number is conserved in the strong interaction, while the singular number can not be conserved in the weak interaction, so that the properties of strange particles can be properly explained.
At that time, a difficult problem was found in the decay process of the lightest exotic particle (now called K meson), namely the so-called"θ - τ" difficult。The difficulty lies in that two kinds of particles with the same mass, lifetime and charge were found in the experiment, one is called theta meson, and the other is called tau meson.The difference between the two particles is that the θ meson decays into two π mesons, while the τ meson decays into three π mesons.By analyzing the experimental results, it can be concluded that the total angular momentum of the three pions is zero and the parity is negative, while if the total angular momentum of the two pions is zero, the parity can only be positive.Since the three terms of mass, life and charge are the same, these two particles should be the samedecayIn terms of behavior, if parity should be conserved, θ and τ cannot be the same particle.
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Research achievements of Li Zhengdao and Yang Zhenning
In 1956, Li Zhengdao and Yang Zhenning made a comprehensive investigation of the history and the current situation. They pointed out that the key to this problem was that people believed that the parity of microscopic particles must be conserved in the process of motion. In the process of strong interaction and electromagnetic interaction, parity conservation was tested, butWeak interactionIn the process of,ParityIt has not been tested decisively, and there is no basis to say that it must be conservative.
Strange particles are a classSubatomic particleThe general name of.The opposite of strange particles is ordinary particles, including protons, neutrons, pions and other ordinary particleshadronandLepton。In 1947, G. D. Rochester and C.C. Butler (1922 -) discovered Λ in cosmic rayszero、Κzero、Κ+And other particles with strange properties.In 1953, more exotic particles were found in the accelerator.Different from ordinary particles, strange particles are always produced quickly and at least two at the same time in strong interactions, and then slowly decay into non strange particles through weak interactions.
Gelman and other research achievements
In 1953, American physicist Gailman and Japanese physicistDongfu NakanoK. Nishijima independently proposed a new quantum number - singular number to explain the properties of strange particles.The singular number can only be taken as an integer, and it is specified that the singular number of ordinary particles is 0. The singular number of singular particles is specified by the following reaction:
π + p → Λzero+ Κzero
ProvisionszeroThe singular number of the particle is+1, ΛzeroThe singular number of the other particles is determined by other reactions.
The singular particle with singular number S=+1 haszero、Κ+Etc.
The singular particle with singular number S=- 1 has-、Λzero、Σ+、Σ-、ΣzeroEtc.
Strange particle with singular number S=- 2zero、Ξ-Etc.
The singular particle with singular number S=- 3 has Ω-Etc.
In the strong interaction, the singular particles co produce, and the singular number S is strictly conserved.Strange particles can decay into several ordinary particles independently, which takes a long time and is realized through weak interaction.In the weak interaction, the singular number S can be nonconservative, Δ S=0, ± 1.
If parity can not be conserved in the process of weak interaction, the θ - τ problem will be solved easily.
