What is Electron and positron: Definition and 20 Discussions

Electron–positron annihilation occurs when an electron (e−) and a positron (e+, the electron's antiparticle) collide. At low energies, the result of the collision is the annihilation of the electron and positron, and the creation of energetic photons:

e− + e+ → γ + γAt high energies, other particles, such as B mesons or the W and Z bosons, can be created. All processes must satisfy a number of conservation laws, including:

Conservation of electric charge. The net charge before and after is zero.
Conservation of linear momentum and total energy. This forbids the creation of a single photon. However, in quantum field theory this process is allowed; see examples of annihilation.
Conservation of angular momentum.
Conservation of total (i.e. net) lepton number, which is the number of leptons (such as the electron) minus the number of antileptons (such as the positron); this can be described as a conservation of (net) matter law.As with any two charged objects, electrons and positrons may also interact with each other without annihilating, in general by elastic scattering.

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  1. D

    Diagonalizing of Hamiltonian of electron and positron system

    What I did was first noting that ##\hat{\vec{S}}_1\cdot\hat{\vec{S}}_2=\frac{1}{2}(\hat{\vec{S}}^2-\hat{\vec{S}}_1^2-\hat{\vec{S}}_2^2)##, but these operators don't commute with ##\hat{S}_{1_z}## and ##\hat{S}_{2_z}##, this non the decoupled basis ##\ket{s_1,s_2;m_1,m_2}## nor the coupled one...
  2. P

    Electron and positron collision producing a b0 meson pair

    Conservation of Energy: 9GeV + E = 5.3GeV + 5.3GeV Therefore E = 1.6GeV for the threshold energy. How would I find the velocity of B0 mesons so that I can calculate their mean distance? Then it would just be distance = velocity of b0 * mean proper lifetime Right?
  3. D

    I Electron and positron annihilate

    Hi. I am just starting to self-study particle physics. Came across the following in some notes - Electron and positron annihilate to form a photon with zero momentum. I thought all photons had momentum due to the de Broglie equation ? Also 2 electrons scatter to form a photon with zero energy...
  4. J

    I Evaluating 2D Delta Function Integral - Any Help Appreciated

    I am quite new here, and was wondering if anybody knows how this 2D integral is evaluated. $$ \int_{-\infty}^\infty \int_{-\infty}^\infty \delta(k_1 x-k_2y)\,dx\,dy$$Any help is greatly appreciated! Thanks!
  5. Tareq Naushad

    B Life of free electrons in space

    If I shoot some free electrons detached from any atom in space from a space station what happens to the electrons? I know around the atom's nucleus electron creates cloud like movement having various energy levels. But what type of movement , cloud and energy the electron holds in absence of any...
  6. A

    Why must an electron-positron collision produce gamma rays?

    Or, more specifically, what determinates the frequency of the photons emitted by a such a collision. I know that the number of photons produced depends on the spin and energy states of the initial particles.
  7. Paradox101

    What is the recoil velocity of a carbon atom in pair production?

    Q. If a photon travels in an electric field(usually by a nucleus,such as ^12C),it can spontaneously disintegrate into an electron and a positron--known as pair production. A)Calculate the smallest possible photon frequency that produces pair production by assuming that both electron and positron...
  8. C

    Pair Production, electron and positron from isolated photon

    I don't completely understand why an electron positron pair cannot be created from an isolated photon. I understand it must have something to do with 4 momentum conservation, but I really can't see a problem given the photon has enough energy for the mass to energy vice versa conversion.\ The...
  9. R

    What happens when an electron and positron collide

    I was listening to this radio program (Google: In Our Time Antimatter) and they kept saying that when an electron and a positron collide they annihilate and radiate energy. I have a feeling that that's not right. I have a hunch that the particles turn into something else which then radiates...
  10. S

    Can photon capture give electron and positron opposite charge

    Is it possible, in theory, that the physical entity electron e(-) and its charged opposite positron e(+) both obtained their respective electric charges by simultaneous capture, by a more fundamental quantum entity (call it FQE), of a quantum of photon with zero rest mass having equal amounts of...
  11. T

    Photon decay into Electron and Positron

    Homework Statement Show that the energy momentum conservation forbids the reaction (gamma)-> positron + electron, Gamma is a photon, which is chargeless and massless Homework Equations E(photon)=hf p(photon)=hf/c Conservation of Energy Conservation of Momentum 4-momentum The Attempt at a...
  12. I

    Feynman diagram of electron and positron annihilation

    Hi all, I am learning Feynman diagrams, and I have a quick question: in diagrams such as the one for electron-positron annihilation (see http://en.wikipedia.org/wiki/Feynman_diagram#Electron-positron_annihilation_example) why is it that the line "in the middle" is that of an...
  13. E

    Annihilation of electron and positron

    Homework Statement A positron with kinetic energy 2.2MeV collides with an electron at rest, and annihilate each other. a. Calculate the average energy of the two gamma photons produced as a result of annihilation Homework Equations The Attempt at a Solution I would infact...
  14. K

    Electron and Positron Annihilation

    Homework Statement An electron traveling at 0.8c annihilates with a positron that is at rest, producing two photons. One of the produced photons travels in the direction of the electron. Determine the energy of each of the photons.Homework Equations p_{photon} = \frac{E}{c} P_{electron} =...
  15. D

    Electron and Positron system

    Homework Statement The system consists of an electron and a positron, which are rotating around each other. Using Bohr's theory of the hydrogen atom, what are possible orbits' radius (from the system mass center) and possible energy equation. Homework Equations The Attempt at a...
  16. I

    What is the orbital frequency of an electron and positron 2.00nm apart?

    A positron is an elementary particle identical to an electron except that its charge is . An electron and a positron can rotate about their center of mass as if they were a dumbbell connected by a massless rod. What is the orbital frequency for an electron and a positron 2.00nm apart? My...
  17. E

    Electron and positron length contraction q.

    Homework Statement In the stanford linear accelerator, electrons and positrons are fired at each other at 50Gev. In the lab, each electron and positron beam is 1cm long. (a) how long is each bundle in its frame? (b) what is the proper length of the accelerator for a bundle to have both its...
  18. K

    Photon as composite of electron and positron

    A photon annihilates into an electron and a positron (both having spin 1/2). The reverse process is also a reality. Can the photon therefore be viewed as a composite of an electron and a positron having a total spin 1?
  19. U

    Electric fields of electron and positron that undergo pair annihilation.

    Here is a question, which may seem dumb: Consider an electron and a positron that annihilate, both of which are non-relativistic (taking the observer's frame of reference to be the center of mass frame of the electron-positron pair) so that we only consider their electric fields for simplicity...
  20. P

    Electron and positron annihilation

    Problem:An electron flies toward +x direction with velocity of 0.9c, while a positron flies toward -y direction with the same velocity. Assuming their speed is so fast that they collide and annihilate at the origin, what will be the magnitude and the direction of the wave vector of the generated...