Antimaterials

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Antimaterial and annihilation
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• The most studied is the annihilation of an
  electron-positron pair. At low energies of the
  colliding electron and positron, as well as in
  the annihilation of their bound state -
  positronium - this annihilation reaction gives in
  the final state two or three photons, depending
  on the orientation of the electron and positron
  spins. At energies of the order of several MeV,
  multiphoton annihilation of an electron-positron
  pair also becomes possible. At energies of the
  order of hundreds of MeV, mainly hadrons are
  produced during the annihilation of an
  electron-positron pair.

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• The annihilating particle and the antiparticle do
  not have to be of the same type Thus, the
  dominant decay of the charged pi-meson p ? µ
  ?µ is due to weak annihilation of a pair of
  quarks of different types du into a virtual W
  boson, which then decays into a pair of leptons
  1. The process of annihilation of a positive
  muon with an electron, similar to the
  annihilation of a positron with an electron, is
  considered. This process has not yet been
  observed experimentally, since the lepton number
  conservation law does not allow a muon-electron
  pair (unlike a positron-electron pair) to
  electromagnetically annihilate into photons and
  requires weak annihilation into neutrinos. For
  example, in muonium, a quasi-atom consisting of µ
  and e -, the calculated probability of
  annihilation into a pair of neutrinos µ e - ?
  ?µ?e is only 6.6 10-12 of the probability of
  ordinary muon decay

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• The annihilation of a nucleon-antinucleon pair
  (for example, an antiproton with a proton or
  neutron) was also studied. In fact, in the
  interaction of antinucleons with nucleons (and in
  general of antihadrons with hadrons), it is not
  the hadrons themselves that annihilate, but the
  antiquarks and quarks that make up the hadrons.
  Moreover, quark-antiquark pairs that are part of
  one hadron also annihilate. Thus, the neutral
  pi-meson p0 consists of a quantum-mechanical
  combination of quark-antiquark pairs uu and dd
  its decay into two photons occurs due to the
  annihilation of such a pair

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• There are not only electromagnetic annihilation
  processes (like the above processes of
  annihilation of electron-positron and
  quark-antiquark pairs into photons, as well as
  decays of neutral vector mesons into lepton
  pairs, for example, decay of a rho-meson into an
  electron-positron pair), but also a "weak" and
  strong annihilation due to the weak and strong
  interactions, respectively. An example of weak
  annihilation is two-particle lepton decays of
  pseudoscalar 2 charged mesons (such as K ? µ
  ?µ), caused by the annihilation of the
  quark-antiquark pairs included in the mesons into
  the virtual vector boson W , which then decays
  into a pair of charged and neutral leptons (for
  the above example with a positive K-meson K
  (us) ? W (virtual) ? µ ?µ). At high
  energies, processes of weak annihilation of a
  fermion-antifermion (i.e., quark-antiquark or
  lepton-antilepton) pair into a real W - or Z
  0-boson are also observed, and the weak
  annihilation cross section increases with
  increasing energy, in contrast to the
  electromagnetic and strong

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• An example of strong annihilation are some decays
  of quarkonia heavier than a neutral pion (J / ?
  meson, ? meson, etc.). Quarks in them can
  annihilate with the participation of a strong
  interaction of two or three gluons, depending on
  the total spin, although such processes are
  usually suppressed by the Okubo - Zweig - Iizuki
  rule . Then the gluons turn into quark-antiquark
  pairs

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• The reverse process of annihilation is the
  creation of particle-antiparticle pairs. Thus,
  the creation of an electron-positron pair by a
  photon in the electromagnetic field of an atomic
  nucleus is one of the main processes of
  interaction of a gamma quantum with matter at
  energies above 1 MeV.

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