Positron-Electron Annihilation - two questions

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Discussion Overview

The discussion revolves around positron-electron annihilation, specifically addressing the energy dynamics involved in the process and the outcomes of collisions at particle accelerators. Participants explore the production of gamma photons and other bosons, as well as the implications of excess energy in these interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions what happens to the excess energy of positrons and electrons after they are converted into gamma photons, noting that the photons' energy should exceed 511 keV due to the initial kinetic energy of the particles.
  • Another participant agrees that the excess energy is transmitted to the photons, suggesting that their energy will be much larger than the rest mass energy of 511 keV, which applies only when the particles are at rest.
  • A participant seeks references for further learning about the topic, indicating interest in deeper understanding.
  • Information is provided about the LEP collider at CERN, detailing its operation and the types of particles produced during electron-positron collisions, including Z0 and W+/- bosons, depending on the energy levels of the collisions.
  • Participants discuss the importance of exceeding the rest mass energy threshold for particle creation in collisions.

Areas of Agreement / Disagreement

There is some agreement on the transmission of excess energy to the photons, but the discussion includes multiple viewpoints regarding the specifics of energy dynamics and the outcomes of the annihilation process. The topic remains unresolved with participants expressing different aspects of the phenomenon.

Contextual Notes

Participants have not fully resolved the implications of excess energy in positron-electron annihilation, and there are varying interpretations of the energy dynamics involved. The discussion also highlights the dependence on the energy levels of the colliding particles and the conditions under which different bosons can be produced.

Who May Find This Useful

This discussion may be useful for individuals interested in particle physics, particularly those studying annihilation processes, energy dynamics in collisions, and the production of fundamental particles in high-energy environments.

what_are_electrons
At the colliders, positrons and electrons are accelerated at MeV, GeV levels on their way to making head-on collisions. Various Bosons can be produced. The most discussed type seems to be the two Gamma Photons (511 keV). Question #1: What happens to the XS energy of the positrons and electrons after they have been "converted" into the two gamma photons?

When I use SLAC's EGS software which has an upper limit of 200 MeV for accelerating positrons, I use liquid hydrogen as the target and look at the results, which include gamma ray emission, electron emission and positron scattering, but none of the other possible bosons. I have used as few as 10 positrons and the max of 100 positrons in the simulation, but I see only about a 10% production of gamma rays. Question #2. What am I overlooking?
 
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what_are_electrons said:
At the colliders, positrons and electrons are accelerated at MeV, GeV levels on their way to making head-on collisions. Various Bosons can be produced. The most discussed type seems to be the two Gamma Photons (511 keV). Question #1: What happens to the XS energy of the positrons and electrons after they have been "converted" into the two gamma photons?
The excess energy is transmitted to the photons in this case, ergo the photons' energy will be much, much larger than simply 511keV. That number, by the way, applies to the annihilation of an electron-positron that are both at rest.
 
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anti_crank said:
The excess energy is transmitted to the photons in this case, ergo the photons' energy will be much, much larger than simply 511keV. That number, by the way, applies to the annihilation of an electron-positron that are both at rest.

Do you have a reference I can learn more from?
 
http://www.pparc.ac.uk/Rs/Pp/Sp/Artcl/LEP.asp

The 27 kilometre circumference LEP machine at CERN (the European Laboratory for particle physics) ran from 1986 until 2000, colliding electrons with their antimatter partners, positrons.

When an electron and a positron collide, they disappear in a burst of energy which, almost immediately, changes back into particles. LEP was designed so that the collisions took place inside four detectors where the particles produced could be studied in detail. PPARC was involved in funding the construction and operation of three of these detectors: ALEPH (Apparatus for LEP Physics at CERN), OPAL (the Omni-purpose Apparatus at LEP) and DELPHI (Detector with Lepton, Photon and Hadronic Identification at LEP.

The nature of the particles generated in these collisions depends upon the speed, or energy, of the colliding electrons and positrons. Between 1989 and 1995 their energy was tuned exactly to the value needed to create Z0 particles, the neutral carrier of the weak nuclear force. Between 1996 and 2000, the collision energy was increased to produce two heavier particles, the W+ and W-, the charged carriers of the weak neutral force. The detection and study of millions of these three particles has allowed LEP to make extremely precise tests of the standard model of particles and their interactions.

Although the LEP project has now finished, with the collider being removed to make way for the Large Hadron Collider which is to be built in the same tunnel, the analysis of the enormous quantity of data generated by the LEP experiments continues.

See also - http://van.hep.uiuc.edu/van/qa/section/New_and_Exciting_Physics/Antimatter/20031005144616.htm

Also, check out the pdf file at Feynman Diagrams and Electron-Positron Annihilation It's a good overview.

Particles occur above some energy threshold (the rest mass), i.e. the total energy involved must exceed the rest energy of the particle that is to be created.
 
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