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Name: Phil G.
Status: other
Age: old
Location: N/A
Country: N/A
Date: 2001-2002


Question:
Pair production cross-sections If two particles, with kinetic energy (in the centre of mass frame) exceeding 2mc^2, collide sufficient surplus mass-energy is available to produce an electron-positron pair. If one or both of the particles is a lepton is there any conservation law that forbids this process?

If so, references please. If not, has any theoretical pair production cross-section ever been published for electron-electron collisions?


Replies:
Phil,

I am not aware of any such conservation laws. At the same time, I am not aware of any such collisions. If none exist, it would not surprise me. Getting a high energy electron to collide with an electron would be difficult to make happen. If it did happen, it would be difficult to track.

Electrons are too small. Hitting a bowling ball with a bullet is hard enough. Hitting a bullet with a bullet is often not worth trying. Mass of an electron is also too small. To make a proton have enough extra energy to produce an electron-positron pair is fairly easy. The proton mass is huge compared to an electron. Not much speed is required (compared to the speed of light). To give an electron that much extra energy would require relativistic speeds (near the speed of light). This can cause the electron to do things like emitting photons before the collision occurs.

Detection is difficult. Although detecting an electron is fairly easy, you won't know which electron you are seeing: incoming, target, produced. You would have to detect the positron and identify it as such, or else detect all three electrons.

I am sorry I could not be more definite about things. If nothing is available, now you understand why. Have a good day.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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