Information AboutAntiparticle |
| CATEGORIES ABOUT ANTIPARTICLE | |
| antimatter | |
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Corresponding to each kind of Particle , there is an associated antiparticle with the same Mass and Spin . Some particles, such as the Photon , are identical to their antiparticle; such particles must have no Electric Charge , but not all charge-neutral particles are of this kind. The laws of nature were thought to be symmetric between particles and antiparticles until CP Violation experiments found that Time-reversal Symmetry is violated in nature. The observed excess of Baryon s over anti-baryons in the universe is one of the primary Unsolved Problems in Cosmology . Particle-antiparticle pairs can annihilate each other if they are in appropriate Quantum State s. They can also be produced in various processes. These processes are used in today's Particle Accelerator s to create new particles and to test theories of Particle Physics . High energy processes in nature can create antiparticles. These are visible in Cosmic Ray s and in certain Nuclear Reaction s. The word Antimatter properly refers to (elementary) antiparticles, composite antiparticles made with them (such as Antihydrogen ) and to larger assemblies of either. HISTORY Experiment In 1932 , soon after the prediction of Positron s by Paul Dirac , Carl D. Anderson found that cosmic-ray collisions produced these particles in a Cloud Chamber — a Particle Detector in which moving Electron s (or positrons) leave behind trails as they move through the gas. The Electric Charge -to- Mass ratio of a particle can be measured by observing the curling of its cloud-chamber track in a Magnetic Field . Originally, positrons, because of the direction that their paths curled, were mistaken for electrons travelling in the opposite direction. The antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the University Of California, Berkeley . Since then the antiparticles of many other subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of Antimatter have been assembled out of antiprotons and positrons, collected in electromagnetic traps. Hole theory
Solutions of the Dirac Equation contained negative energy quantum states. As a result, an electron could always radiate energy and fall into a negative energy state. Even worse, it could keep radiating infinite amount of energy because there were infinitely negative energy states available. To prevent this unphysical situation from happening, Dirac proposed that a "sea" of negative-energy electrons fills the universe, already occupying all of the lower energy states so that, due to the Pauli Exclusion Principle no other electron could fall into them. Sometimes, however, one of these negative energy particles could be lifted out of this Dirac Sea to become a positive energy particle. But when lifted out, it would leave behind a ''hole'' in the sea which would act exactly like a positive energy electron with a reversed charge. These he interpreted as the Proton , and called his paper of 1930 ''A theory of electrons and protons''. Dirac was aware of the problem that his picture implied an infinite negative charge for the universe. Dirac tried to argue that we would perceive this as the normal state of zero charge. Another difficulty was the difference in masses of the electron and the proton. Dirac tried to argue that this was due to the electromagnetic interactions with the sea, until Hermann Weyl proved that hole theory was completely symmetric between negative and positive charges. Dirac also predicted a reaction e + p → γ + γ (electron and proton annihilate to give two Photon s). Robert Oppenheimer and Igor Tamm proved that this would cause ordinary matter to disappear too fast. A year later, in 1931, Dirac modified his theory and postulated the Positron , a new particle of the same mass as the electron. The discovery of this particle the next year removed the last two objections to his theory. However, the problem of infinite charge of the universe remains. Also, as we now know, Bosons (if they exist) also have antiparticles, but since they do not obey the Pauli exclusion principle, hole theory doesn't work for them. A unified interpretation of antiparticles is now available in Quantum Field Theory , which solves both these problems. PARTICLE-ANTIPARTICLE ANNIHILATION ''Main article: Annihilation ''. pair which influences the propagation of a Kaon causing a neutral kaon to ''mix'' with the antikaon. This is an example of Renormalization in Quantum Field Theory — the field theory being necessary because the number of particles changes from one to two and back again.]] If a particle and antiparticle are in the appropriate quantum states, then they can annihilate each other and produce other particles. Reactions such as e+ + e- → γ + γ (the two-photon annihilation of an electron-positron pair) is an example. The single-photon annihilation of an electron-positron pair, e+ + e- → γ cannot occur because it is impossible to conserve energy and momentum together in this process. The reverse reaction is also impossible for this reason. However, in . PROPERTIES OF ANTIPARTICLES | ||
| ::<b>CPT p,σ,n>   |   (-1)<sup>J-σ</sup> p,-σ,n<sup>c</sup>>,</b> |
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| ::<b>H   |   ∑<sub>k(+)</sub> E(k) a<sup>+</sup><sub>k</sub> a<sub>k</sub>  +  ∑<sub>k(-)</sub> E(k) b<sup>+</sup><sub>k</sub> b<sub>k</sub>  +  E<sub>0</sub>,</b> |
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| Where <b>E<sub>0</sub></b> Is An Infinite Negative Constant The | "http://wwwinformationdelightinfo/encyclopedia/entry/vacuum_state" class="copylinks">Vacuum State is defined as the state with no particle or antiparticle, ie, <b>a<sub>k</sub> 0> = 0</b> and <b>b<sub>k</sub> 0> = 0</b> Then the energy of the vacuum is exactly <b>E<sub>0</sub></b> Since all energies are measured relative to the vacuum, <b>H</b> is positive definite Analysis of the properties of <b>a<sub>k</sub></b> and <b>b<sub>k</sub></b> shows that one is the annihilation operator for particles and the other for antiparticles This is the case of a Fermion |
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