antiparticle

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American Heritage Dictionary:

an·ti·par·ti·cle

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(ăn'tē-pär'tĭ-kəl, ăn'tī-) pronunciation
n.
A subatomic particle, such as a positron, antiproton, or antineutron, having the same mass, average lifetime, spin, magnitude of magnetic moment, and magnitude of electric charge as the particle to which it corresponds but having the opposite sign of electric charge, opposite intrinsic parity, and opposite direction of magnetic moment.


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A counterpart of an ordinary subatomic particle, which has the same mass and spin but the opposite charge. Certain other properties are also reversed, including the magnetic moment. An encounter between a particle and its corresponding antiparticle–for example, an electron and a positron–results in their mutual annihilation.
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antiparticle, elementary particle corresponding to an ordinary particle such as the proton, neutron, or electron, but having the opposite electrical charge and magnetic moment. Every elementary particle has a corresponding antiparticle; the antiparticle of an antiparticle is the original particle. In a few cases, such as the photon and the neutral pion, the particle is its own antiparticle, but most antiparticles are distinct from their ordinary counterparts.

When a particle and its antiparticle collide, both can be annihilated and other particles such as photons or pions produced. In some cases this represents the total conversion of mass into energy. For example, the collision between an electron and its antiparticle, a positron, results in the conversion of their combined masses into the energy of two photons. The reverse process, pair production, is the simultaneous creation of a particle and its antiparticle from the particles that result from their mutual annihilation.

The existence of antiparticles for electrons was predicted in 1928 by P. A. M. Dirac's relativistic quantum theory of the electron. According to the theory both positive and negative values are possible for the total relativistic energy of a free electron. In 1932, Carl D. Anderson, while studying cosmic rays, discovered the predicted positron, the first known antiparticle. About 23 years passed before the discovery of the next antiparticles-the antiproton was discovered by Owen Chamberlain and Emilio Segrè in 1955 at the Univ. of California, and the antineutron was discovered the following year-but the existence of antiparticles for all known particles was by then firmly established in theory.

The existence of antiparticles makes possible the creation of antimatter, composed of atoms made up of antiprotons and antineutrons in a nucleus surrounded by positrons. A very simple type of "atom" incorporating antiparticles is positronium, a brief pairing of a positron and an electron that may occur before their annihilation; it was first created and identified in the laboratory in 1951. Di-positronium, a molecule consisting of two positronium, was created in 2007. A few simple nuclei of antimatter have been created in the laboratory, such as the antideuteron (see deuterium). In 1995 nine atoms of antihydrogen (a single positively charged positron orbiting a single negatively charged antiproton) were created at CERN (near Geneva, Switzerland) by an Italian-German team headed by Walter Oelert.

Any antimatter in our part of the universe is necessarily very short-lived (the antihydrogen atoms, for example, survived for only 40 billionths of a second) because of the overwhelming preponderance of ordinary matter, by which the antimatter is quickly annihilated. Although scientists for a time considered the possibility that entire galaxies of antimatter could have evolved in a part of the universe far removed from our own, observations now indicate that this is not the case. The experimental work of Val L. Fitch and James W. Cronin in 1964 demonstrated an asymmetry in matter/antimatter reactions that may explain why the universe is composed mostly of matter. For their discovery, they shared the 1980 Nobel Prize in Physics. In 2010 an eight-year study of B meson decay at the Fermi National Accelerator Laboratory found a tendency to produce roughly 1% more muon pairs than antimuon pairs.


In physics, a rare form of subatomic matter that is a mirror image of normal matter. The antiparticle corresponding to an elementary particle has the same mass as the particle but is opposite in all other properties. The antiparticle corresponding to an electron is a positron, which has the same mass as an electron but a positive charge. Antiprotons have the same mass as protons but a negative charge. When matter and antimatter come together, the two particles annihilate each other, converting their mass into energy or into other types of particles.

  • As far as scientists can tell, there is almost no naturally occurring antimatter in the universe, although it is possible to make antimatter in particle accelerators.
  • Random House Word Menu:

    categories related to 'antiparticle'

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    Random House Word Menu by Stephen Glazier
    For a list of words related to antiparticle, see:
    • Nuclear and Particle Physics - antiparticle: particle that has the same mass and spin as its subatomic counterpart but opposite charge and magnetic moment


    Translations:

    Antiparticle

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    Dansk (Danish)
    n. - antipartikel

    Nederlands (Dutch)
    antideeltje

    Français (French)
    n. - antiparticule

    Deutsch (German)
    n. - (phys.) Antiteilchen

    Ελληνική (Greek)
    n. - (φυσ.) αντισωματίδιο, αντισωμάτιο

    Italiano (Italian)
    antiparticella

    Português (Portuguese)
    n. - antipartícula (f) (Fís.)

    Русский (Russian)
    античастица

    Español (Spanish)
    n. - antipartícula

    Svenska (Swedish)
    n. - antipartikel (fys.)

    中文(简体)(Chinese (Simplified))
    反粒子

    中文(繁體)(Chinese (Traditional))
    n. - 反粒子

    한국어 (Korean)
    n. - 반입자

    日本語 (Japanese)
    n. - 反粒子

    العربيه (Arabic)
    ‏(الاسم) غير قابل للتجز‏

    עברית (Hebrew)
    n. - ‮חלקיק תת-אטומי עם אותה מסה כשל חלקיק נתון אך עם מטען הפוך, אנטי-חלקיק‬


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    conjugate particles (particle physics)
    antideuteron (atomic physics)
    antilepton (atomic physics)
    charge conjugation operation (particle physics)