Positron-Electron Annihilation - two questions

[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?

[anti_crank]

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.

[what_are_electrons]

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?

[Astronuc]

The Large Electron Positron Collider (LEP) (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 - Electron-Positron annihilation (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 (http://departments.weber.edu/physics/schroeder/feynman/) 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.

[what_are_electrons]

Fantastic! Many many thanks. Especially to the link that is your talk in PDF. http://departments.weber.edu/physics/schroeder/feynman/AnnihilationTalk.pdf

Vince

[Astronuc]

The pdf file is a talk given by Daniel V. Schroeder.
Department of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508
USA

http://departments.weber.edu/physics/schroeder/