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

    Feynman diagram for pair annihilation

    Hi, I've been reading about Feynman diagrams lately and I'm trying to understand the pair annihilation diagram. The picture's here: http://en.wikipedia.org/wiki/File:Feynman_EP_Annihilation.svg I don't understand the following things about the diagram: 1. Why anti-patricles have to...
  2. bcrowell

    Why can't we detect neutrino-antineutrino annihilation?

    Various astrophysical processes produce antineutrinos, which then fly off into outer space. I assume there are pretty accurate estimates of the production rates. I can imagine three possible fates for such an antineutrino: (1) annihilating with a neutrino, (2) interacting with baryonic matter...
  3. G

    Photon and anti-photon annihilation?

    Photon and "anti-photon" annihilation? In quantum field theory pairs of virtual particles can appear from vacuum and quickly annihilate each other, for example an electron/positron or a proton/antiproton. But how does this work with photons?From what I know, the photon is its own anti-particle...
  4. Q

    Annihilation and potential energy?

    Sorry, brand new here and this may be in the wrong place or very obvious. When matter and antimatter annihilate is the energy released the sum of all their potential energy? does E=MC2 only work because of the specifics of our universe, and if the universe were to contain more matter (and...
  5. T

    Evaluating annihilation and creation operators

    1. Evaluate the following (i.e. get rid of the operators)...
  6. A

    Fermionic creation and annihilation

    Hi guys, I consider fermionic holes and I know the creation and annihilation operators of them. I have shown that \vec{S}= \sum\limits_{k \nu \mu} \frac{1}{2} \bf{c}_{k \mu}^{\dagger} \vec{\sigma}_{\mu \nu} \bf{c}_{k \nu} =...= \sum\limits_{k \nu \mu} \frac{1}{2} \bf{h}_{-k \mu}^{\dagger}...
  7. A

    Is the energy generated from matter-antimatter annihilation useful?

    I understand that when matter and antimatter come in contact with each other, they annihilate to generate either gamma rays or other particles such as pions, electrons, etc. So my question is, how do we use the gamma rays or the particles to say move a spaceship from one point to another...
  8. D

    Annihilation of electron positron pair

    Suppose in thought experiment one electron positron pair is annihilated in the carriage of fast moving train while the other pair is annihilated on the platform . Will the frequency of the photon reaching the platform from the carriage will be same as given out by the other pair which which is...
  9. W

    Can an annihilation operator be found for this Hamiltonian?

    Homework Statement Given the Hamiltonian H(t) = \frac{P^2}{2m} + \frac{1}{2}mw^2X^2 + b(XP+PX) from some b>0. Find an annihilation operator a_b s.t. [a_b,a_b^{\dagger}]=1 and H = \hbar k (a_b^{\dagger}a_b+\frac{1}{2}) for some constant k. Hint: [P + aX,X]=[P,X], \forall a.Homework Equations...
  10. Doofy

    Quantum harmonic oscillator, creation & annihilation operators?

    For a set of energy eigenstates |n\rangle then we have the energy eigenvalue equation \hat{H}|n\rangle = E_{n}|n\rangle. We also have a commutator equation [\hat{H}, \hat{a^\dagger}] = \hbar\omega\hat{a}^{\dagger} From this we have \hat{a}^{\dagger}\hat{H}|n\rangle =...
  11. C

    Why annihilation of matter/antimatter occurs in dual pairs?

    Just a question. A particle and a corresponding antiparticle (e.g. electron and positron) can annihilate by mutual interaction, producing energy (photons). If the process of mutual annihilation occurs necessarily between particles and antiparticles (matter and antimatter), we would expect...
  12. B

    Understanding Antimatter Annihilation: Levels and Possibilities"

    At what level does annihilation occur? For example, if I've got an up quark and an anti-up quark, they can annihilate. If I've got a proton (uud) and anti-proton (anti up, anti up, anti down), they can annihilate. What if I mix a neutron (down, down, up) with an anti-proton (anti up, anti up...
  13. K

    Creation, annihilation and motion

    I'd like to know if creation and annihilation operators are involved in a free trajectory of a particle from point A to point B. If it's the case, how so? If there is a detector at A, and another one at B, mathematically speaking, can it be said that the particle is annihilated at A, and...
  14. S

    Deuterium + Antideuterium Annihilation

    Does anyone have a reference for the details of energy and by-products produced in an annihilation reaction of a matter deuterium atom [np]e- with anti-matter antideuterium atom [p^{\overline{}}n^{\overline{}}]e+ (note: is there a better Latex code for putting bar to show antimatter ?) As I...
  15. phosgene

    Why 2 photons are formed from positron-electron annihilation at rest

    This isn't a homework question, though it kind of relates to a practical I did recently. Sorry if it's posted in the wrong section! So, why are only 2 photons formed from positron-electron annihilation at rest? I understand why you can't have just one, as then you won't get conservation of...
  16. L

    Wick theorem for particle-antiparticle annihilation

    I am trying to write down the LSZ formula for e- e+ -> 2 gamma: $$ S_{fi} \propto \langle 0| T \{\bar{\Psi}(x_1) \vec{A}(x_2) \Psi (x_4) \vec{A}(x_3) \left\lbrack \frac{(-i)^2}{2} \int d^4x A_\mu (x) \bar{\Psi}(x) \gamma^\mu \Psi (x) \int d^4y A_\nu (y) \bar{\Psi}(y) \gamma^\nu \Psi (y)...
  17. J

    Matter/antimmatter annihilation

    I know that matter and corresponding antimatter particles annihilate giving energy and, conversely a photon can give a pair of particle / antiparticle. Perhaps this is a candid question, but is it only an empiric finding? or is there other reason? In fact the two particles of the pair have...
  18. L

    Creation and annihilation operators

    In one dimensional problems in QM only in case of the potential ##V(x)=\frac{m\omega^2x^2}{2}## creation and annihilation operator is defined. Why? Why we couldn't define same similar operators in cases of other potentials?
  19. Fosheimdet

    Momentum increased in electron-positron annihilation?

    Homework Statement An electron and a positron is on a collision course. Both have a speed of 1,80*10^8 m/s. What are the frequencies of the two photons created after the electron and the positron has annihilated? Electron mass=positron mass= 9,11*10^-31 kg Homework Equations...
  20. B

    Is Information Preserved in Annihilation Processes?

    Hi, i have a question, what's about Einstein 'information keeping' law in matter and antimatter annihilation process, is any information left after this process ?
  21. M

    Proton + Antiproton annihilation

    I'm asked to state whether or not a proton and an antiproton can annihilate into an electron, a positron, and an electron neutrino. p + \overline{p} \rightarrow e + e^+ + \nu_e It doesn't seem allowed to me but I can't fully justify it with any conservation law. I've reasoned that...
  22. M

    Particle/Antiparticle annihilation

    p + \bar{p} \rightarrow W^+ + W^- I'm just going through various "Is this particle annihilation/decay possible" questions and came across this one...then started thinking...then started over-thinking. Is this possible? It seems because the W bosons are so much more massive than the protons it...
  23. R

    Pair production and pair annihilation

    what are pair production and pair annihilation phenomena?
  24. V

    Electron/Positron Annihilation

    I recently read a textbook that stated without explanation "When a positron collides head on with an electron, the energy of each photon is the sum of one particle's rest and kinetic energy." So E = m_o*c^2 + K. However my question is, why isn't the energy of each photon twice the mass and...
  25. I

    Particle Annihilation in Interacting Fields: Frequency and Bound State Quanta

    I need some advice. I have read that interacting fields can lead to quanta annihilation? How often does this happen, and can bound state quanta annihilate or is it just free quanta? Thanks
  26. J

    Creation and Annihilation Operators

    We know that a|n> = √n | √(n-1)> and a' |n> = √(n+1) | n + 1 > so, If we use this to find <n|a'a|n> it would be equal to n <n|a'a|n> = n Am I correct? I'm not really sure about my calculations. I operate with a first so. <n|a'a|n> <n|a' √n | √(n-1)> = n ...
  27. C

    WIMP annihilation cross section

    Hi, I'm reading an article called SuperSymmetric Dark Matter, by G. Jungman et al. doi:10.1016/0370-1573(95)00058-5 and in section 3.2, he claims that <σv> ≈ \alpha^{2}(100 GeV)^{-2} \approx10^{-25} cm^{3} s^{-1},[\itex] for \alpha \approx \frac{1}{100}. When I run through the calculation...
  28. L

    Creation and annihilation operators

    Hi all Homework Statement Show: (a^\dagger a)^2=a^\dagger a^\dagger a a +a^\dagger a wheres: a= \lambda x +i \gamma p a^\dagger= \lambda x -i \gamma p Homework Equations - The Attempt at a Solution Well, I haven't got much. I just tried to use the stuff given, put it into my...
  29. S

    Exploring Particle-Antiparticle Annihilation Possibilities

    I've been searching about particle-antiparticle annihilation and I've been wondering whether it was possible for particle to annihilate with antiparticle that is not its pair? Can annihilation occur with collision of different particle-antiparticle quarks(e.g. up antiquark and strange quark)...
  30. P

    Blackhole and Anti-Blackhole Annihilation

    Ok I am wondering what would happen if an anti-black hole collided with a black hole of the same mass. Would they annihilate and release energy or would it become a more massive or less massive black hole?
  31. A

    Antimatter Annihilation in Angels & Demons

    Hello, Last night I rented Angels & Demons and observed a number of physical flaws. I noticed that the explosion following the annihilation of the antimatter in the canister was not as intense as what I had expected, which may not be a flaw as I am merely a novice in the realm of physics...
  32. Y

    Creation annihilation operators - expanding brackets

    I would like to normal order the following product of creation-annihilation operators, set up in Maple 16 as follows. The problem is, Maple won't perform "expand" (lowercase e) on the last step below (evaluating sigma3(x) :=[op1+op2]*[op3+op4]*[op5+op6] ); , which makes setting up the entire...
  33. Einj

    Silly question about pair annihilation

    Hi all. I have a (probably stupid) question about e^{+}e^{-} annihilation. I was reading about the emission of two 511keV photons which is the electron's mass. But, is this energy fixed every time e^{+}e^{-} annihilates in a two photons or is just the energy of the positronium dacay? My idea...
  34. TrickyDicky

    Exploring the Stability of Quark-Antiquark Annihilation in Pseudo-Scalar Mesons

    I was wondering, for instance in a neutral pion or the j/ψ meson, what prevents quark-antiquark annihilation during its short lifetime? I mean what allows them to be particles, shouldn't annihilation be inmediate? is it the time it takes quark and antiquark to collide inside the particle?
  35. C

    Neutrino Antineutrino annihilation possible?

    As far as I know, the anihilation of an electron by a positron is an electromagnetic process described by QED. Neutrinos, however, do not participate in the elektromagnetic interaction. Does that mean a Antineutrino will not anihilate a Neutrino of the same kind? Is there an interaction between...
  36. 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...
  37. S

    Angular momentum during Annihilation of Positron-electron

    1. During the annihilation of positron and electron AT REST, two photons are generally created at opposite direction - angle between them being 180 degres. However, an electron that is orbiting around an atom can sometimes react with a positron. The orbital electron in that case has therefore...
  38. K

    How much energy does annihilation take?

    Many people say that when mixing matter with anti-matter , energy is released according to e=mc2 however how much energy does it take to mix matter with antimatter which leads to annihilation .
  39. P

    Electron annihilation - what happens to gravity

    It is my understanding (?) that, when an electron is annihilated, the resulting photons do not react with gravity. Why isn't that quality conserved?
  40. 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...
  41. J

    Early annihilation of antimatter

    If a positron can be seen as an electron moving backwards in time technically, could it be that antimatter was annihilated near the beginning of the universe because it could go no further backwards in time that at the moment of the big bang, leaving only matter going forward in time?
  42. S

    Regarding pair production and annihilation

    Hi, i have a few questions about these two processes. Now, I am only 16 years old, in my last year of school, so I am not so familiar with physics, if you could put terms simple enough for an average 16 year old to understand, i'd much appreciate it :) my question is: If e‾ + e+ → γ + γ and γ →...
  43. S

    Proton, anti Proton annihilation help

    I have been told when a proton and anti proton annihilate only the one up and one anti up quark destroyed forming ∏+ and ∏- measons. I don't understand how both protons are not fully annihilated? anti proton has: anti up, anti up and anti down quarks proton has: up, up down quarks Any...
  44. M

    Proton, antiproton annihilation

    Need help with this question. What are the wavelengths of the two photons produced when a proton and antiproton at rest annihilate? Any help is appreciated, thank you :)
  45. N

    Particle annihilation and creation

    I'm just working on a particle physics assignment and seem to be a little stuck on one concept. I have a positron-electron to two scalar particles and a photon-photon -> electron-positron problem. The issue I'm having with it is that the only way I really know how to handle them is with the...
  46. Q

    Complete annihilation of light through polarizers

    Hi, when i am doing an experiment that uses two polarizers (Cross) to achieve complete annihilation of light, why am i not able to see complete darkness when i look at the light source from the end of the polarizers, but rather the light source changes to a different color for example...
  47. M

    Conjugation of creation and annihilation operators - Fock's

    Hi, I'm doing some exercise about second quantization. In a exercise about spiorial field I have to explicitly write the Hamiltonian of a Majorana-Langrangian, in terms of operators of creation and annihilation: A_{\vec{k},\lambda} that acts on Fock's space. The point is that during the...
  48. L

    Annihilation operator acting on a Fock state

    I'm trying to show: a(p)|q1,q2,...,qN> = \sumNi=1(2pi)32Ep\delta(3)(p-qi)x|qi,...,qi-1,qi+1,...,qN> I'm pretty sure you have to turn the ket into a series of creation operators acting on the vacuum |0>, but then not sure what relations need to be invoked for it to be clear. Any help...
  49. T

    How much energy is released from an electron-positron annihilation?

    More specifically, I am wondering what the energy released is when the electromagnetic force is also included in this calculation. In the case where the electron and positron are at a distance d, the energy released would be the mass energy (1.022 MeV) plus the energy that resulted from the...
  50. V

    Analytic function, creation and annihilation operators proof

    Homework Statement Show that f(a†a)a† = a†f(a†a + 1) Where f is any analytic function and a and a† satisfy commutation relation [a, a†] = 1. The Attempt at a Solution I have used [a, a†] = aa†-a†a=1 to write the expression like f(a†a)a†= a†f(aa†) but I don't know what to do...
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