Positron-Electron Annihilation - two questions

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In summary, at colliders such as the 27 km circumference LEP machine at CERN, positrons and electrons are accelerated at MeV, GeV levels and collide to produce various bosons, including the two Gamma Photons (511 keV). When the positrons and electrons collide, they are "converted" into the two gamma photons and the excess energy is transmitted to the photons, resulting in a much larger energy than simply 511 keV. However, this energy depends on the speed of the colliding particles and can be tuned to create specific particles, such as the Z0 or W+ and W-. The analysis of data from these collisions has allowed for precise tests of the standard model of particles and their interactions. The process
  • #1
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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  • #2
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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  • #3
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?
 
  • #4
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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  • #6

1. What is positron-electron annihilation?

Positron-electron annihilation is a process in which a positron (a positively charged particle) and an electron (a negatively charged particle) collide and produce two gamma rays. This process occurs when a positron and an electron are in close proximity to each other and their opposite charges cause them to attract and then annihilate each other.

2. How does positron-electron annihilation occur?

Positron-electron annihilation occurs when a positron and an electron collide and their opposite charges cause them to attract and then annihilate each other. This process produces two gamma rays with a combined energy equal to the mass of the positron and electron multiplied by the speed of light squared (E=mc^2).

3. What are the applications of positron-electron annihilation?

Positron-electron annihilation has various applications in industries such as medicine, materials science, and astrophysics. In medicine, positron emission tomography (PET) uses positron-electron annihilation to produce images of the body to diagnose and monitor diseases. In materials science, positron annihilation spectroscopy is used to study defects and properties of materials. In astrophysics, positron-electron annihilation is used to study high-energy processes in celestial objects.

4. Can positron-electron annihilation be reversed?

No, positron-electron annihilation cannot be reversed. When a positron and an electron collide, they are completely annihilated and transformed into energy in the form of two gamma rays. This process is a fundamental law of physics known as conservation of energy, and it states that energy cannot be created or destroyed.

5. How does positron-electron annihilation contribute to our understanding of the universe?

Positron-electron annihilation allows scientists to study the properties of matter and antimatter, which helps us understand the fundamental building blocks of the universe. It also provides valuable information about high-energy processes and celestial objects. Additionally, positron-electron annihilation is used in experiments to test theories such as the Standard Model of particle physics, which helps us understand the behavior of particles and their interactions.

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