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In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. [1]
The electron–positron annihilation process is the physical phenomenon relied on as the basis of positron emission tomography (PET) and positron annihilation spectroscopy (PAS). It is also used as a method of measuring the Fermi surface and band structure in metals by a technique called Angular Correlation of Electron Positron Annihilation ...
Pair production and annihilation: In the Stückelberg–Feynman interpretation, pair annihilation is the same process as pair production: Møller scattering: electron-electron scattering Bhabha scattering: electron-positron scattering Penguin diagram: a quark changes flavor via a W or Z loop Tadpole diagram: One loop diagram with one external leg
In many subfields of physics and chemistry, the use of these operators instead of wavefunctions is known as second quantization. They were introduced by Paul Dirac. [2] Creation and annihilation operators can act on states of various types of particles.
Feynman diagram of electron/positron annihilation. The electron–positron annihilation interaction: e + + e − → 2γ. has a contribution from the second order Feynman diagram: In the initial state (at the bottom; early time) there is one electron (e −) and one positron (e +) and in the final state (at the top; late time) there are two ...
The annihilation into a neutrino–antineutrino pair is also possible, but the probability is predicted to be negligible. The branching ratio for o -Ps decay for this channel is 6.2 × 10 −18 ( electron neutrino –antineutrino pair) and 9.5 × 10 −21 (for other flavour) [ 3 ] in predictions based on the Standard Model, but it can be ...
Both the scattering and annihilation diagrams contribute to the transition matrix element. By letting k and k' represent the four-momentum of the positron, while letting p and p' represent the four-momentum of the electron, and by using Feynman rules one can show the following diagrams give these matrix elements:
In the early years, ACAR was mainly used to investigate the physics of the electron-positron annihilation process. In the 1930s several annihilation mechanism were discussed. [ 8 ] [ 9 ] [ 10 ] Otto Klemperer could show with his angular correlation setup that the electron-positron pairs annihilate mainly into two gamma quanta which are emitted ...