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. (talk)

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  1. S

    Question about Feynman diagram showing annihilation

    This is Feynman diagram of annihilation I get from wikipedia https://en.wikipedia.org/wiki/Annihilation I don't understand what the middle line with arrow to the right is. If I consider the left vertex and conservation of charge, it means the horizontal line with arrow to the right should carry...
  2. P

    I How Do Positrons Reach Cloud Chambers Without Annihilating?

    I was researching on the Anderson cloud chamber that discovered the positron in 1932. I couldn't help but wonder, if positron annihilates upon contact with an electron, how was it able to get till the cloud chamber without annihilation? Shouldn't the 2 photons be the only thing observed in the...
  3. H

    I Boltzmann equation for annihilation

    In the Dodelson's textbook, the author introduce the Boltzmann equation for annihilation. ##a^{-3} \frac{d(n_1 a)}{dt} = \int \frac{d^3 p_1}{(2 \pi)^3 2E_1} \int \frac{d^3 p_2}{(2 \pi)^3 2E_2} \int \frac{d^3 p_3}{(2 \pi)^3 2E_3} \int \frac{d^3 p_4}{(2 \pi)^3 2E_4} \times (2 \pi)^4 \delta^3 (p_1...
  4. K

    B What are the differences between relict and relic?

    Dear PF Forum, It's been a while since I logged in PF Forum. And wish you a good health. I'd like to ask a question concerning anti matter. I read in Dan Brown's Angel and Demon that anti matter can be used as energy source. A ha, I said to myself. There were you went wrong mr. Author. The...
  5. richard_andy

    A Relation between the density matrix and the annihilation operator

    This question is related to equation (1),(3), and (4) in the [paper][1] [1]: https://arxiv.org/abs/2002.12252
  6. DiracPool

    B Particle creation and annihilation

    I read somewhere that when, say, an electron and positron annihilate, they create two photons which travel in opposite directions in order to conserve linear momentum. Is this true? What about pair production. Do you likewise need two photons to do this? Or, can you do it with one photon...
  7. J

    B Could Dark Matter/Energy be the byproduct of annihilation?

    I’m not super familiar with the physics of this but, from a statistical standpoint it would make sense since so much annihilation was taking place after the Big Bang, and most of our universe is dark energy and matter. Further we know annihilation creates energy why not the opposite of energy...
  8. Bruno Cardin

    A Expectation value in Heisenberg picture: creation and annihilation

    So, I have a hamiltonian for screening effect, written like: $$ H=\sum_{k}^{}\epsilon_{k}c_{k}^{\dagger}c_{k}+ \frac{1}{\Omega}\sum_{k,q}^{}V(q,t)c_{k+q}^{\dagger}c_{k} $$ And I have to find an equation for the time evolution of the expected value of the operator ##c_{k-Q}^{\dagger}c_{k}##. I...
  9. R

    B Regarding electron-positron annihilation

    When an electron meets an anti-electron which is also known as positron and collide, the particles will become photons. But where did the photons go after the electron-positron annihilation happened?
  10. E

    A How can we show that the annihilation operators satisfy the given equation?

    I don't really know what I'm doing, I'd appreciate some nudges in the right direction. We defined ##\mathcal{S}## as the space of complex solutions to the Klein-Gordon equation, and for any ##\alpha, \beta \in \mathcal{S}## that ##(\alpha, \beta) =-\int_{\Sigma_0} d^3 x \sqrt{h} n_a j^a(\alpha...
  11. Z

    B Does special relativity entail matter annihilation?

    hello Does special relativity entail matter annihilation ?
  12. F

    Annihilation: calculation of photon energies

    I set up this problem this way: ##p_a^{\mu}=(E, \sqrt{E^2-m^2}, 0, 0)## ##p_b^{\mu}=(m, 0, 0, 0)## ##p_c^{\mu}=(2E_\gamma, 2E_\gamma, 0, 0)## I have chosen to consider the two photons as a single particle of energy equal to ##2E_\gamma##. At this point I applied conservation of the...
  13. F

    Electron-positron annihilation, photon emission angle

    I consider the laboratory system. The four momentums in this reference system are respectively: ##p^\mu = \big(\sqrt{|p|^2+m^2}, 0, 0, |p| \big)## ##p'^\mu= \big(m, 0, 0, 0 \big)## ##k^\mu = E\big(1, 0, 1, 0\big)## ##k'^\mu = E'\big(1, 0, -\sin \varphi, \cos \varphi \big)## I used conservation...
  14. D

    B Particle annihilation -- Is it instantaneous?

    During particle annhilation the rest mass of the particle pair gets converted into momentum with zero time component ie. light. As the pair is colliding do their rest masses decrease and get converted to momentum as a function of distance? Or do they instantaneous annihilate in a discrete interval?
  15. P

    B 1-photon emission possible from electron-positron annihilation?

    I was reading about electron-positron annihilation. Typically it results in two photons, each with an energy of 511 keV, that go shooting out in opposite directions. But I read that in some instances three photons can result. Electrons have an intrinsic spin of ½, while photons have a spin of 1...
  16. chocopanda

    Quantum Mechanics: creation and annihilation operators

    Hello everyone, I'm new here and I'm struggling with the mathematical formalities in quantum mechanics. $$\langle n+1|b^\dagger bb^\dagger + \frac 12 |n \rangle = \langle n+1|b^\dagger bb^\dagger |n \rangle + \langle n+1| \frac 12 |n \rangle $$ $$ = \langle n+1|b^\dagger b \sqrt{n+1} |n+1...
  17. Simon Bridge

    A Conservation of angular momentum in positron-electron annihilation

    Pretty much in a nutshell... fielded a question about how spin affects electron positron annihilation... ie do the spins have to be opposite in order to conserve angular momentum for two-photon annihilation to happen? Intuitively I figured that looks reasonable ... but decided to check, and...
  18. Physicsphysics

    Pion annihilation Feynman diagram

    π+ + π- → γ + γ How do you represent this in a Feynman diagram showing the individual quark? I am very confused please help! [Moderator's note: Moved from a technical forum and thus no template. Own effort below.]
  19. Tanmoy

    Annihilation operators of two different types of Fermions

    IfA=cd, where c and d are annihilation operators of two different types of Fermions, then {A,A°}is? A.1+n1+n2 B.1-n1+n2 C.1-n2+n1 D.1-n1-n2 Where,n1 and n2 are corresponding number operator, A° means A dagger or creation operator,as the particles are fermions they will obey anti-commutation I think
  20. F

    B Anti-matter and matter annihilation

    Does anti-matter and matter annihilate each other even if they are not same "type" (eg. neutron and positron) and they meet each other?
  21. N

    Have you seen Pacific Rim? What did you think of it?

    Doom: Annihilation 2019 has just been released October 1, 2019 and I just watched it. I think it is better than the Original Doom flick by the Rock. What is your thought? This is the synopsis (it's not a spoiler): "Follows a group of UAC Marines as they respond to a distress call from a top...
  22. geoelectronics

    I High Energy Physics: Positron-Electron Annihilation

    [Moderator's note: Post edited to remove the homework header.] High school physics demonstrations teach and show us that a positron and an electron must be at rest with their environment before they can join together and annihilate. The process makes them disappear and they are replaced by two...
  23. Q

    A Explicit form of annihilation and creation operators for Dirac field

    I'm unclear on what exactly an annihilation or creation operator looks like in QFT. In QM these operators for the simple harmonic oscillator had an explicit form in terms of $$ \hat{a}^\dagger = \frac{1}{\sqrt{2}}\left(- \frac{\mathrm{d}}{\mathrm{d}q} + q \right),\;\;\;\hat{a} =...
  24. Vamsi9955

    I The energy released from antimatter annihilation -- New uses?

    The pure energy released from antimatter annihilation can there be any use of this clean energy for research purposes like the use of light in LIGWO for gravitational waves study can we use it efficiently like light in LIGWO I think we can and it could lead us to reveal mysteries of universe
  25. A

    A Helicity and electron/positron annihilation

    Hello everybody! I have a question regarding the process ##e^+ e^- \rightarrow Z/\gamma \rightarrow f \bar{f}##, where ##f## is a fermion and ##\bar{f}## is an antifermion. I am studying the process to understand LEP measurements. Supposing of being in ultrarelativistic regime, so helicity and...
  26. chmodfree

    To prove that a coherent state is an eigenstate of the annihilation operator

    The definition of coherent state $$|\phi\rangle =exp(\sum_{i}\phi_i \hat{a}^\dagger_i)|0\rangle $$ How can I show that the state is eigenstate of annihilation operator a? i.e. $$\hat{a}_i|\phi\rangle=\phi_i|\phi\rangle$$
  27. B

    B But WHY do antimatter and matter annihilate on contact?

    Everyone knows that matter and antimatter annihilate upon contact. But exactly WHY this should happen is not at all obvious, at least to me. So what exactly happens when two such particles encounter one another that leads them to disappear in a large release of photons? And for that matter...
  28. G

    I Annihilation vs. Creation Operators: What's the Difference?

    Cohererent states are defined as eigenstates of the annihilation operator. Never the creation operator is referred to. Is this just a convention or is more behind? What is the essential difference between eigenstates of the annihilation- versus the creation operator? Thank you very much in...
  29. C

    I How close do electrons and positrons have to be to interact?

    Electrons and positrons are assumed to be point masses. Two points presumably can never actually touch. How close do they have to be before they annihilate each other?
  30. D

    Number operator on wavefunction

    Homework Statement Consider the state $$\psi_\alpha = Ne^{\alpha \hat a^\dagger}\phi_0, $$ where ##\alpha## can be complex, and ##N = e^{-\frac{1}{2}|\alpha|^2}## normalizes ##\psi_\alpha##. Find ##\hat N \psi_\alpha##. Homework Equations $$\hat N = \hat a^\dagger \hat a$$ $$\hat a\phi_n =...
  31. Paul Colby

    I Gluon creation and annihilation operators

    Hi, When one quantizes EM the resulting gauge boson, the photon, ends up being its own antiparticle. From what I read of gluons, they have anti particles. I can follow how anti particles come about quantizing a complex-valued field like that for electrons. For the spin 1/2 case non-interacting...
  32. RicardoMP

    Bosonic annihilation and creation operators commutators

    Homework Statement After proving the relations ##[\hat{b}^{\dagger}_i,\hat{b}^{\dagger}_j]=0## and ##[\hat{b}_i,\hat{b}_j]=0##, I want to prove that ##[\hat{b}_j,\hat{b}^{\dagger}_k]=\delta_{jk}##, however I'm not sure where to begin. 2. The attempt at a solution I tried to apply the...
  33. Sophrosyne

    B Creation and annihilation operators in particle physics

    I was recently reading about annihilation and creation operators in particle physics using the model of an harmonic oscillator, and then quantizing it. This is fine. I can understand it. But how does this quantization of the energy of the harmonic oscillator manifest physically? Is it that only...
  34. M

    Creation and Annihilation operators on photons

    Homework Statement The possible (normalized) eigenstates of a photon in a given system are written as: $$|\psi_1>,|\psi_2>,...|\psi_m>$$ Let another state be $$|\phi> = \frac{|\psi_1>+|\psi_2>+...+|\psi_m>}{\sqrt{m}}$$ and denote: $$|n>=|\psi_1>|\psi_1>...|\psi_1>$$ which represent a state...
  35. caitphys

    Muon production and decay from relativistic annihilation

    Homework Statement An antiproton of energy 35 ##GeV## from a source outside the solar system interacts with a proton in the upper atmosphere traveling on a trajectory which is radial with respect to the centre of the Earth. The antiproton annihilates the proton with the final outcome that two...
  36. S

    I Understanding Spin to Particles & Annihilation

    Hello! I am a bit confused about the idea of spin. Let's say we have spin ##1/2## particles. This means that the spin along a random axis is ##\pm 1/2##, right while the values of the particle spin (i.e. the module) is actually ##\sqrt{1/2(1+1/2)}##? Also I am a bit confused about combining...
  37. Eric Walker

    B Exploring Electron-Positron Annihilation & Gravitation

    I have been trying to understand the implications of a thought experiment and am interested to know either where it's going off course or what those implications might be. Through some reading of earlier threads on this forum I have verified my starting hunch that photons bend spacetime despite...
  38. H

    B Entanglement and pair-production and annihilation

    I am confused about entanglement, but I am not a physicist. The concept sounds cool and I want to understand in a way so that it is familiar with what I already know. I want to know if I am interpreting this right: 1) If we have a photon that produces a pair of electron and positron, the...
  39. Aarav Sangar

    B Energy density of annihilation

    <Moderator's note: Two threads on the same topic merged in order to have arguments and sources at one place.> Can antimatter-matter be used as a fuel for a rocket? There are various problems for anti-matter to be used as a fuel as it produces a lot of gamma rays. Gamma rays are not healthy to...
  40. G

    Potential energy and annihilation

    Let's assume an electron and an anti-electron are in a gravitational field so they both have potential energy. What will become of this energy if they annihilate? Will the momentum of the photons after the annihilation will increase so the total energy will be conserved? Thanks for answering!
  41. B

    A R value in electron positron annihilation

    In the calculation of R=σ(e+e-→hadrons)/σ(e+e-→μ+μ-) from BaBar experimental data at a center of mass energy of √s≈10 GeV i obtain R=5. Theoretically I should get a value of R=10/3. I know it has something to do with the resonances of ϒ mesons shown in the plot attached, but I don't know how to...
  42. Adgorn

    Annihilator of a Direct Sum: Proving V0=U0⊕W0 for V=U⊕W

    Homework Statement Suppose V=U⊕W. Prove that V0=U0⊕W0. (V0= annihilator of V). Homework Equations (U+W)0=U0∩W0 The Attempt at a Solution Well, I don't see how this is possible. If V0=U0⊕W0, then U0∩W0={0}, and since (U+W)0=U0∩W0, it means (U+W)0={0}, but V=U⊕W, so V0={0}. I don't think this...
  43. A

    I Annihilation and production of bosons

    I am confused about the production of bosons in annihilation processes. If we have a positron and an electron coming together and annihilating, we can always find a frame in which the net momentum is zero, which would suggest that a single photon can never be produced in such an interaction...
  44. L

    Find the energy of a photon after this annihilation process

    Homework Statement [/B] The problem is as follows: in a reference frame there is one electron at rest and one incoming positron which annihilates with the electron. The positron energy is E and two gamma rays are produced. Find first the energy of the photons in the center of mass frame as...
  45. G

    A Is the matter-antimatter annihilation observable in priciple

    The youngest epoch of the universe we can observe so far is the CMB. It is theorized that systematic and accurate measurement of gravitational waves could allow us to "see" events from even earlier cosmic epochs. If we go to even earlier cosmic epochs we have what must have been a very singular...
  46. Buzz Bloom

    I Q re early universe matter-antimatter annihilation

    I have seen several estimates that the period during the early universe in which almost all the protons, neutrons, anti-protons, and anti-neutrons (P, N , AP, AN) were annihilated occurred about 1 second after the big bang. I conceptualize this as a period in which as the temperature cooled...
  47. I

    A What Are the Spin States of W Bosons and How Do They Affect Annihilation?

    How can a couple of W bosons annihilate each other, if both are left-handed particles? (there are no right handed Ws)
  48. S

    B Matter-antimatter annihilation and inflation

    Is there any link between the energy released from the annihilation of matter-antimatter during baryogenesis and cosmic inflation or expansion/dark energy? This question came up when reading: https://www.nasa.gov/mission_pages/chandra/news/08-160.html
  49. S

    A Electron-positron pair annihilation

    Consider the following u-channel diagram (on the right) in the link below. https://www.physicsforums.com/attachments/diphoton-png.95147/ Let the polarization vectors of ##k_1## and ##k_2## be ##(\epsilon^{\mu}_{1})^{*}## and ##(\epsilon^{\mu}_{2})^{*}## respectively. Do you label the incoming...
  50. F

    I Create black hole with lasers? Physics project

    Hi! We have a projekt at the university and I have been thinking of creating a tiny tiny black hole after I've read some articles. I know one can create an artificial black hole with polarized laser pulses at a block of glass. And then one can measure a lot of things, usually hawkingradiation...