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. N

    Nate's Question: Why Is Detection Equivalent to Annihilation?

    http://en.wikipedia.org/wiki/Coherent_state#Quantum_mechanical_definition From the link above: "Physically, this formula means that a coherent state is left unchanged by the detection (or annihilation) of a particle." My question is, why is detection of a particle equivalent to...
  2. A

    Delay of virtual particle pair annihilation

    My grasp of physics is limited, however, I am an engineer, thus I am asking for other's assistance in understanding how to delay the annihilation of a virtual particle pair. Most literature I've read, indicates a virtual particle pair is "real" if only briefly. QUESTION: How long is...
  3. S

    Energy from matter-matter annihilation (relation to Dark Matter)

    Hi PF Would it be theoretically possible to create energy (for example photons) from matter-matter annihilation (not using anti-matter), so that we could create a powerplant based on this, without the need of producing anti-matter for the energy production? I know that Dark Matter WIMP's...
  4. N

    Can creation and annihilation operators be used in interaction case?

    In the free case,we decomposite the free Hamiltonian into the creation and annihilation operators, i just wonder why this ad hoc method can not be used to the interaction theory?
  5. D

    Do H- annihilation spectra vary with element?

    Do \bar{H} annihilation spectra vary with element? If \bar{H} collides (slowly, at 10 Kelvin for example) with H, Beryllium, Lead, does it make a difference?
  6. C

    Derivation of creation and annihilation operator commutation relations

    Hi, I'm hopng someone can help me. I've begun working my way through Lahiri's "A first book of quantum field theory". In chapter 3 he shows the Fourier decomposition of the free field is given by \phi(x) = \int \frac{d^3 P}{\sqrt{(2\pi)^3 2E_p}} (a(p) e^{-ip\cdot x} + a^D(p) e^{ip...
  7. Islam Hassan

    Why is Annihilation Not a Force?

    If no other force is responsible for annihilation, is it a force in itself? Does one always need a gauge boson in order to have a force? If so, can one consider that matter and antimatter are their own gauge bosons with annihilation? IH
  8. D

    Parallel velocity hydrogen/antihydrogen annihilation at relativistic speeds.

    They've just now kept antihydrogen in a bottle for some 15 minutes. Suppose we inject some H and measure the annihilation photon energies. Then we accelerate the mixture (somehow) to a velocity around .99c and measure the energies of those photons that are emerging orthogonal to the...
  9. M

    Can a Single Photon Carry All the Momentum in Electron-Positron Annihilation?

    Hi, I understand that momentum before and after annihilation must be conserved. However, why isn't it possible to have a net momentum not equal to zero before hand, (ex. an electron and a positron traveling head on, but at different velocities) and then just have a single photon travel in...
  10. D

    Exploring Proton-Antiproton Annihilation: Energy and Results Explained

    I recently checked this link... http://en.wikipedia.org/wiki/Proton_antiproton_annihilation It says that...For proton-antiproton annihilation at 2 GeV, one final state result is p + p → π0 + γ1 + γ2 + γ3 + γ4 with γ1 and γ3 ~125 MeV each, γ2 and γ4 ~530 MeV each...
  11. N

    Independent virtual particle after mind experiment annihilation

    Independent virtual particle after "mind experiment" annihilation Hello good people, Probably a bit of a silly question, but I have been entertaining a bit of a thought experiment about the following. Consider the following: 1. A virtual photon is exchanged between two electrons to...
  12. A

    Electron/Positron Annihilation

    Hi everyone, I'm currently studying a bit of quantum theory and I came across this paragraph: When an electron collides with a positron, it moves with an angle theta_1 with the normal. Ditto for the positron, except that it has an angle theta_2. But the two angles must be equal. Why...
  13. T

    Annihilation and Creation operator problem

    I've looked through all my course notes, but I just don't even know where to start with this problem. The problem: \langle 1 \mid x^2 \mid 2 \rangle Use the annihilation and creation form for x to obtain the above matrix element. What I do know: I know that x = \sqrt{\hbar /...
  14. M

    Definition of fermionic annihilation operators

    Hi, I'm revising for an exam and I came across a past paper that has a question on annihilation operators, It asks what happens when acting on a wavefunction with a group of different creation/annhilation operators (all identical fermions.. It's quite simple apart from the fact that it...
  15. D

    Annihilation of Matter/Antimatter

    When anti matter and matter come into contact do they only annihilate each other leaving everything else undisturbed? Or does the resulting energy destroy/tear apart nearby particles? The reason I ask, assuming that the result is the former, if antimatter were to be harnessed could...
  16. E

    Quark - antiquark annihilation

    Hi there! If an electron collides with a positron, they will annihilate producing a photon. But what about quarks? If an up quark collides with an antiup quark, do they produce a gluon or a photon? I ask that because I'm studying the reaction: \Pi^- + p \rightarrow \Lambda+K^0 where I suppose...
  17. M

    Resoance states and quark annihilation

    I've been looking at interactions between K mesons and "ordinary" matter such as protons and neutrons. Since I can't put a bar over a letter, I'll let a CAPITAL letter stand for an ANTI-quark. sD + duu ---> suu + uU (thru a resonance baryon suu ++) I know this one is possible, but what...
  18. A

    Quantum mechanics - creation and annihilation operators

    Homework Statement Evaluate <n|p^2|n> where p is the momentum operator for the quantised harmonic oscillator. Homework Equations creation operator: a+|n>=sqrt(n+1)|n+1> annihilation operator: a|n>=sqrt(n)|n-1> The Attempt at a Solution the operator p can be defined in terms of...
  19. F

    Electrostatic energy in annihilation process

    When an electron and a positron annihilate, they typically produce two gamma rays, each of energy mc^2 plus whatever kinetic energy available before annihilation. I was recently told that it is an experimental fact that the electrostatic energy between the electron and the positron does NOT...
  20. T

    Annihilation of Electron by Positron to Produce at least 2 Gamma Rays

    Homework Statement The problem is listed as follows: Show that conservation of energy and momentum require at least two gamma rays to e emitted in the annihilation of an electron by a positron. Homework Equations p(initial) = p(final) E(initial) = E(final) Total rest mass = 1.0218...
  21. H

    Can Particle Pair Annihilation Produce Only One Photon?

    1. Problem Statement What is the wavelength of each of the two photons produced when a particle pair of a positron and electron accelerated at 25GeV collide? Can the net result of this annihilation be only ONE single photon? Why or why Not? Homework Equations Etotal(initial) =...
  22. A

    Mass, fine structure constant & annihilation

    Hi, If the mass is very high and the fine structure constant very small, is it true particles of opposite charge can't annihilate? If yes. What has mass and fine structure constant got to do with annihilation?
  23. alemsalem

    Particle- antiparticle annihilation, how is it understood?

    How do physicists understand or "visualize" annihilation without Dirac's hole theory?
  24. D

    Understanding Energy in Annihilation: Proton-Antiproton vs. Neutron-Antineutron

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  25. O

    Parity Transformation of Annihilation Operator

    Homework Statement Given that, for operators A and B: \mathrm{e}^{\mathrm{i} \alpha A} B \mathrm{e}^{-\mathrm{i} \alpha A} = \sum_{n=0}^{\infinity} {(\mathrm{i}\alpha)^n \over n!} B_n where B_0 = B and B_n = [A, B_{n-1}] for n=1,2,... show that: P_1...
  26. P

    Annihilation of two particles / Rest mass energy

    I haven't used the template because I just need some reassurance on understanding a topic, not help with a question! When two particles annihilate (e.g. proton and antiproton), the resulting radiation will have a minimum energy of the sum of the rest mass energies of the two particles, right...
  27. N

    Why the annihilation must be between a couple of particle and counterpart antipartic?

    Please teach me about this: Why the annihilation between particles must be particle and coresponding anti particle.Example:electron can annihilate positron create a virtual photon,after that,virtual photon create a couple muyon and antimuyon.But why can't be there exist the annihilation between...
  28. O

    Derive expression for Klein-Gordon annihilation operator

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  29. S

    Annihilation Operators: Prove af(a^\dagger)|n>=df(a^\dagger)/da|0>

    So we all know about a and a^\dagger. My problem says that if f(a^\dagger) is an arbitrary polynomial in a^\dagger then af(a^\dagger)|n> = \frac{df(a^\dagger)}{da}|0> where |0> is the ground state energy. How can I go about proving this? A hint would be highly appreciated. Thanks,
  30. S

    Is there some reverse of annihilation?

    When heavy nuclei split up we get energy,when light nuclei join together we get energy. When elemental particles split up in annihilation we get energy (photons). What if we join certain photons together?Could we obtain energy in this way and make analog of nuclear fusion?
  31. U

    Why does this Bra Ket (with creation and annihilation operators) equal zero?

    1. Explain why <n|(a-a+)^3|n> must be zero 2. a and a+ (a dagger) are the raising and lowering operators (creation and annihilation operators). 3. Because it says explain, I am not sure any mathematical proof is needed. I am best answer is that because (ignoring that the bracket...
  32. D

    Fermion creation and annihilation operators

    Hi. If c and c^\dagger are fermion annihilation and creation operators, respectively, we know that cc^\dagger+c^\dagger c=1 and cc=0 and c^\dagger c^\dagger=0. I can use this to show the following [c^\dagger c,c]=c^\dagger cc-c c^\dagger c=-cc^\dagger c=-c(1-cc^\dagger)=-c But on the...
  33. J

    Positron - electron annihilation.

    Here is an excerpt from my textbook: "The mass of a Z boson is about 90 Gev. By selecting the energy of the electron and positron beams in the LEP collider to be 45 Gev each, a high rate was achieved for the production of neutrino-antineutrino pairs in the process. The experiment shows that...
  34. P

    Better Understanding Antimatter Annihilation?

    So I am taking an introductory particle physics class, and we have started learning about the leptons and how some particles, like neutrinos, have antiparticle pair based on a different in a different quantum number, like Lepton number. Another example is Neutrion and Anti-Neutron which differ...
  35. R

    Electron - positron annihilation

    Apologies if this question is already covered. I searched, but couldn't get info from pf. when electron-positron annihilation happens..what is emitted ? as per wiki, its gamma rays but on cern website i read that muon pairs(muon and anti muons) are emitted. which one is correct ?
  36. H

    Annihilation and energy occurance

    Can someone be precise and tell how much energy is released when annihilation occurs...let's say proton-antiproton(i.e in MeV),also is there some missing energy in it that is not detected(i.e difference between predicted and observed results in energy generation)
  37. H

    Exploring Matter-Antimatter Annihilation: Energy Ratio and Logical Explanations

    I've heard that matter antimatter annihilation does not produce required mass to energy ratio at the end, i.e either some particles created are not being detected...is this true? Also why does annihilation creates so much energy, any logical explanation?
  38. G

    Is a matter-antimatter annihilation just a particle turning around in time?

    Is a matter-antimatter annihilation just a particle turning around in time, or is it a particle from the present being hit by a partcle from the future (because antimatter is matter going back in time)?
  39. A

    Photon Annihilation, where does the energy go?

    Ok When we look at diffraction, single or double slit, we can obtain the minima and maxima by determining the path lengths and relating that to the wavelength. The idea here is that 1/2 wavelength path difference or 180 deg phase difference result in minima etc. does the The minima, or...
  40. C

    Black Hole Annihilation & Photon Interaction

    Lets say i had a black hole out in space , and then i had another black hole made out of anti-matter , and they came together after they annihilated each other and produced photons , would the photons kind of orbit each other because they could not escape the intense G field , i realize...
  41. haael

    Fermion annihilation operators from position and momentum

    Is it possible to express fermion annihilation operator as a function of position and momentum? I've seen on Wikipedia the formula for boson annihilation operator: \begin{matrix} a &=& \sqrt{m\omega \over 2\hbar} \left(x + {i \over m \omega} p \right) \\ a^{\dagger} &=& \sqrt{m \omega...
  42. 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} =...
  43. S

    Up, anti-up quark annihilation Feynman diagram

    Homework Statement At the Tevatron you observe the process u ̅u → τ+τ−. Draw the lowest order Feynman diagrams for the processes involved and state which interactions are responsible. Label all internal lines, external lines and vertices [u = up quark, τ = tau lepton] The Attempt at a...
  44. J

    Neutrino Annihilation: Validity of Interaction and Lepton Number Conservation

    Homework Statement Is the following process a valid interaction? \nu_\mu \bar{\nu}_e \rightarrow e^+ \mu Homework Equations none The Attempt at a Solution I'm not sure whether lepton number must be conserved at each vertex, or just for the overall process. I can draw a Feynman diagram...
  45. F

    Energy of resulting Gamma Rays after particle annihilation

    Homework Statement An electron and a positron are moving side by side in the +x direction at 0.50c when they annihilate each other creating two gamma rays. What is the energy of each photon? Homework Equations (mc2 + K+) + (mc2 + K-) = E1 + E2 The Attempt at a Solution I solved...
  46. maverick280857

    Energy conservation in e-e+ annihilation

    Hi, I'm trying to convince myself (mathematically) that energy is conserved at the vertex in e^-e^+ annihilation, while solving Exercise 3.5(b) of Halzen and Martin's book (page 83). I am looking at the time dependent term in the scattering amplitude T_{fi} alone, to recover the delta...
  47. R

    QCD Calculation for e+e- Annihilation: Quarks, Gluons, & Hadrons

    In e+e- annihilation, are the jets that are produced quarks and gluons, or hadrons? What is the basic idea behind a QCD calculation for such a process? For example, do I take the two initial states to be e+e-, and the two final states to be q+q- (quark and antiquark), but also add the...
  48. L

    Time dependent annihilation op

    Hi, In the free theory \mid k \rangle=a^{\dag} (\vec{k}) \mid 0 \rangle . Then in Srednicki chapt 5, he defines time-independent operator that he says in free theory creates a particle localized in momentum space about \vec{k_1} as: a^{\dag}_1 \equiv \int f_1 (\vec{k}) a^{\dag}(\vec{k})...
  49. T

    Pion Annihilation: Can Neutral Pions Really Convert to Photons?

    I'm running into a dilemma: I've recently worked out the Feynman rules for Chiral perturbation theory for 2 flavors, and discovered that the term \mathcal{L}=\frac{f_\pi^2}{4} \Tr[(D_\mu U)^\dag (D^\mu U)] seems to contain the term ~ e^2 A_\mu A^\mu \pi^0 \,\pi^0 describing a direct...
  50. S

    Which electron on annihilation will release more energy

    Homework Statement which electron on annihilation will release more energy ,the one at rest or the one in relative motion Homework Equations The Attempt at a Solution
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