What is Annihilation: Definition and 260 Discussions

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. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.During a low-energy annihilation, photon production is favored, since these particles have no mass. However, high-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created.
The word "annihilation" takes use informally for the interaction of two particles that are not mutual antiparticles – not charge conjugate. Some quantum numbers may then not sum to zero in the initial state, but conserve with the same totals in the final state. An example is the "annihilation" of a high-energy electron antineutrino with an electron to produce a W−.
If the annihilating particles are composite, such as mesons or baryons, then several different particles are typically produced in the final state.
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  1. S

    Energy Liberated in Electron/Proton Annihilation

    will the energy liberated be same if the electron and proton are annihilated in the moving carriage of train and on the railway platform
  2. C

    A Query about Pair Production and Electron-Positron Annihilation

    After an electron-positron pair is produced by a high-energy photon hitting the nucleus of an atom, is it possible for the produced positron to annihilate with a bound electron from the very same atom it was produced in? In this situation, what would happen to the produced electron--would it be...
  3. P

    C-Symmetry & P+p_bar Annihilation: Griffiths Ref. C. Baltay et al

    In the first edition of Griffiths' Introduction to Elementary Particles, p. 129, I read: "In strong interactions, charge conjugation invariance requires, for example, that the energy distribution of the charged pions in the reaction p + p_bar -> \pi^+ + \pi^- + \pi^0 should (on average) be...
  4. S

    Creation and annihilation operator in quantum mechanics?

    What is exactly the creation and annihilation operator in quantum mechanics? What its physical significance?
  5. K

    Can annihilation in flight produce higher energy γ-rays?

    I was wondering wether the γ-ray energy produced from the annihilation of a positron with a electron is always given only by the rest mass E=mc^2, that is 1022keV in total. I've read that the positron will slow down almost to rest before annihilation takes place. I've also read in...
  6. N

    A short query on annihilation process

    How does this annihilation process play in semiconductors? Initially i thought that as long as the an electron gets enough energy to move into conduction band (in an energy diagram) - it will move and wander within the Conduction band. However, i have a slide notes about annihilation that talks...
  7. M

    Z Boson, Posiron-Electron Annihilation.

    Suppose I want to find the minimum velocity of the electron and positron required to make a Z boson during annihilation. How would I go about this? I had an attempt which came out at 422ms^-1. This doesn't really seem right... so I'm guessing i made a big mistake...
  8. N

    Electron-pozitron annihilation, conservation of spin

    Hello, I have one question. The most probability annihilation is e+ + e- -> y + y with spins -1/2+1/2=-1+1. But I heard, so, there exist with small probability other combinations of spin. yy is general spin-2 and e+e- is spin-1 and now there is something purportedly with orbitals s, p, d, but I...
  9. J

    Annihilation - matter/antimatter

    sorry for this elementary question. when an electron (matter) and a positron (anitmatter) collide, they annihilate, releasing high energy photons/gamma rays - correct? so, when particle pairs are created within the quantum foam, which pop into and out of existence within the Planck time...
  10. R

    Pair Production and Annihilation

    When a photon, with the help of a nucleus experiences pair production to make a positron and an electron, the energy of the photon will equal the rest mass of both the electron and positron together right? Then when the electron and positron annihilate, the two photons produces will each have...
  11. A

    Expectation value of two annihilation operators

    Hello, I was studying about the effect of a beam splitter in a text on quantum optics. I understand that if a and b represent the mode operators for the two beams incident on the splitter, then the operator for one of the outgoing beams is the following, c = \frac{(a + ib)}{\sqrt{2}}...
  12. S

    Proton-Antiproton Annihilation

    Homework Statement A proton and antiproton at rest in an S-state annihilate to produce \pi0\pi0 pairs. Show that this reaction cannot be a strong interaction. Homework Equations I interpret this problem as: p + p_bar -> \pi0 + \pi0 The Attempt at a Solution If this were a strong...
  13. O

    Antimatter (Proton & Anti-Proton Annihilation)

    In Antimatter production in a labratory, does anyone know the principle element used to generate antimatter such as anti-protons?
  14. M

    Quantum physics- annihilation question

    So I'm looking at my notes, and there's a section on annihilation. It explains that in a particle/ anti-particle collision, momentum is conserved. In the problem, an electron with velocity= 8 x 10^6 m/s collides with a positron with velocity 3 x 10^6 m/s, producing two photons. The equation was...
  15. G

    Observing antiquark annihilation

    When looking for antimatter, we generally look for the electron vs. positron signature of 511 keV. It is my understanding that quarks are always confined in hadrons, and that they are held together by gluons. My questions: - Can quarks be removed from their confinement so that they may...
  16. K

    Big Bang - Gravitational field of antimatter + matter before annihilation

    I posted this question in the general physics section and the physics part has been answered somewhat. However the cosmological components remain un-answered. Would someone be kind enough to comment on those aspects please? Here is the question; Matter and Antimatter, I have always...
  17. S

    Exploring Lepton Annihilation and Hadron Formation in the Standard Model

    Imagine you have electron and positron (leptons) falling towards each other. The interaction between these two is electromagnetic at long distances. It is well established that this reaction eventually leads to annihilation of these two particles. Now consider electron and proton(hadron) falling...
  18. M

    Can e+e- collisions produce e+e- pairs through two-photon processes?

    Hi, I don't think I understand why antimatter annihilates when it touches matter, should I picture has it as if it was a wave that canceled an other one? Or is it something else entirely? Thanks.
  19. Y

    Linearly indep. annihilation operator

    Homework Statement If \varphi and \widetilde{ \varphi } are linearly independent and \hat{N}\varphi=n\varphi and \hat{N}\widetilde{\varphi}=n\widetilde{\varphi}, with n\geq 1 \ \text{Prove that } \hat{a}\varphi_{n} \text{ and } \hat{a}\widetilde{\varphi}_{n} \text{ are also linearly...
  20. P

    Why do antiparticles annihilate on contact with normal matter?

    Hello, everyone. I have searched google and wiki, but have not been able to find the solution to my question. I was wondering why do antiparticles annihilate on contact with normal matter? If someone could help explain this to me or send me a link on where i can get this information it...
  21. H

    Particle creation and annihilation and the remaining fields problem

    lets simulate this simple experiment: creation followed by annihilation of 2 equal particles of type P, here named P1 and P2. (*) assuming the precursors before creation as usual, and also residuals as usual after annihilation. The question is about the remaining fields, gravitational...
  22. R

    Commuting creation and annihilation operators

    Hello, I have the missfortune of having to calculate a commutator with some powers of the creation and the annihilation operators, something like: \left[ a^m , (a^{\dagger})^n \right] I have managed to derive \left[ a^m , (a^{\dagger})^n \right]= m a^{m-1} \left[ a , a^{\dagger}...
  23. D

    Particle/antiparticle annihilation

    particle/antiparticle "annihilation" This has been bugging me for quite some time now. Why is it called "annihilation" when a particle and an antiparticle collide, when in fact they don't annihilate at all, but simply transform into photons with the original energy conserved? Since...
  24. marcus

    A way to see dark matter annihilation (Pamela: cosmic positrons/antiprotons)

    http://agenda.albanova.se/contributionDisplay.py?contribId=389&sessionId=257&confId=355 This came out at the Identification of Dark Matter (IDM-2008) meeting in Stockholm on 18-22 August PAMELA - an experiment searching for dark matter with cosmic antiparticles "The PAMELA satellite...
  25. J

    Pair Annihilation and Conservation of Momentum and Energy Explained

    I'm a little unsure about a certain part of this shown in a book. There is an electron and a positron moving in the +x direction. They annihilate each other and release 2 photons. to conserve momentum 1 moves in the -x and one in the +x direction. So then the first step is to do conservation...
  26. C

    Matter/antimatter annihilation question

    Although this question is simple it's been bugging me: If you were to take one kilo of antimatter and annihilate it with one kilo of matter is the energy (using E=mc^2) released proportional simply to the mass of the matter or to the sum of the masses of both the matter and antimatter? So...
  27. H

    Annihilation, perhaps a defination problem

    [SOLVED] Annihilation, perhaps a defination problem Problem: An electron and an anti-electron undergo mutual annihilation. Which of the following does not have to be conserved? A. Electric charge B. Kinetic energy C. Lepton number D. Momentum Attempt to question: The answer is B but...
  28. B

    Electron-Positron Collisions: Annihilation or Conversion?

    When electrons collide with positrons, we get gamma-rays and other particles. Keeping in mind E=mc^2, is the result better called "annihilation" or "conversion"?
  29. B

    Antiparticle and particle annihilation

    Is there set formulas on how exactly this works. We learned in class very very quickly about how a electron and positron collide and form two photons. There has to be a direct relation between the photons properties and the electron/positron. Thanks
  30. P

    Positron-electron annihilation

    Do the gamma rays (from positron-electron annihilation) must interact to have reversible reaction? I read in my textbook that this reaction is reversible? Is that true? The reaction: ^{0}_{-1}e+ ^{0}_{+1}e \rightarrow 2 \gamma
  31. GRB 080319B

    Matter-antimatter annihilation

    Why, or perhaps how, is 100% of the mass in matter-antimatter annihilation turned into energy? I thought no reaction could be 100% efficient, i.e. 2nd law of thermodynamics? Isn't the Carnot heat engine or the conversion of matter into energy in the accretion disk of a black hole the most...
  32. H

    Annihilation and anti-matter interactions

    Hi, We are learning particle physics at the moment in school. My teacher was telling me that when matter meets anti matter, they annihilate each other out. My question is what happens when an anti proton meets a positron or when an anti neutrino meets an electron. Would they annihilate each...
  33. V

    How do I write a nuclear equation for the annihilation of a positron?

    How do I write a nuclear equation representing the annihilation of a positron with an electron? Do they just cancel out? or do I write energy on the left hand side of the equation?
  34. M

    Electron-positron annihilation as an energy source?

    Why can't we use electron-positron annihilation as an energy source? Unlike antiprotons, positrons sometimes pop out of beta decay and positron-producing isotopes with short half lives are routinely produced in cyclotrons around the world for hospital PET-scanners. Positrons and electrons...
  35. max_emerso

    Conservation of momentum at Annihilation

    If you have a proton and an anti-proton traveling in the same direction with momentum from A to B but during the flight time they become attracted due to their opposite charges and annilhilate, the momentum I would guess is transferred to the resulting unstable K particles mesons etc, which, as...
  36. S

    Positron-electron annihilation in matter

    I have seen some seemingly differing statements in various sources about the dynamics of annihilation when the positron has some kinetic energy and is traveling through a medium. Two sources I've read state or imply that a positron in motion through matter must first lose it's kinetic...
  37. 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...
  38. T

    Pair creation and annihilation

    How did they experimentally verify that there is pair creation and annihilation in the vacuum? What kind of particles usually pops in and out of the vacuum?
  39. malawi_glenn

    Proton anti-proton annihilation.

    Homework Statement state why p + p_bar --> 1 photon is forbidden Homework Equations The Attempt at a Solution I have checked all quantum numbers and they are okay. I wondering altough if p_bar has intrinsic parity -1 (p has parity +1)?? According to the soloution, it is...
  40. T

    Positron - electron annihilation

    Homework Statement A positron having a kinetic energy equal to its rest mass energy mec^2 collides with a stationary electron. The positron and the electron annihilate in the process and two photons are created. What is the maximum possible energy of a photon produced in the...
  41. 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...
  42. N

    Annihilation Operator Hermitian?

    Homework Statement How do I show that the annihilation operator \hat{a} is hermitian WITHOUT explicitly using the condition where an operator X is hermitian if its adjoint is also X ie. X=X^+ Homework Equations none. The Attempt at a Solution I could show \hat{a} \hat{x}...
  43. N

    Harmonic Oscillator-Normalisation & Annihilation Operator

    Homework Statement Wavefunction: \psi(x) = N\sum_{n=0}^\infty \frac{\beta^n}{\sqrt{n!}}\psi_n(x) And \psi_n(x) has eigenvalue E_n = (n + 1/2)\hbar\omega . - Determine N (normalisation constant). - Show \psi(x) is an eigenstate of 'a' (annihilation operator). The attempt at a...
  44. A

    Exploring QM's Theory on Photon Creation and Annihilation

    Does QM tell us that photons are actually electrons and positrons goign through a cycle of annilation and creation?
  45. R

    Big Bang Matter-Antimatter Annihilation

    In as few words as possible, could someone refresh my memory as to why in the Big Bang there was a slight excess of matter that survived the matter-antimatter annihilation? And is such matter just baryons, or was there remaining from the annihilation other forms of matter besides baryons?
  46. T

    Mater Annihilation -matter v.s. anti-matter-

    Mater Annihilation --matter v.s. anti-matter-- hey all, in the study of "massless particles" such as the electron and the and the positron. in beta decay (beta plus) there is an emission of a subatomic particle called the positron (the anti-particle of the electron) my thought is...
  47. G

    Annihilation creation operator

    Hey, I am calculating the expectation value of the position x. I have the wave function psi(x) = |1> + |2> so I use the equation <x> = <psi|(a+a^+|psi> to calculate the mean value. So I get (<1| + <2|)(a+a^+)(|1> + |2>) which I reduce to <1|a|1> + <1|a|2> + <2|a|1> +...
  48. L

    What happens to a field after annihilation?

    When an electron and a positron, for instance, annihilate, do their fields disappear away at c from the point of the annihilation, letting their former influence still apply beyond the vanishing line? If the energy of these particles is entirely in their fields, as I sometimes read, how can...
  49. H

    Neutrino-antineutrino annihilation

    As far as I know the usual extension of the standard model to include a massive neutrino implies a violation of the conservation of quantum numbers, this means the lepton number (since the neutrino is uncharged). During its propagation a massive left-handed neutrino can be regarded as a massive...
  50. P

    Particle Annihilation: Electron-Positron & Photon Energies

    Hey i am doing some studying and when it comes to the subject of nuclear decays it says that when an electron and positron annihilate at rest they produce two photons with equal energys. Can someone try to explain to me why the photons have equal energies and how come there must be two photons...
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