# Electron-positron collisions

## Main Question or Discussion Point

I'm trying to understand electron-positron collisions and I've got a few questions if you don't mind :)

I know hadrons can be created through electron-positron annihilation. Can protons be produced like this? Has it been done before? How much energy would be required? How do you figure the amount of energy needed?

Also, does annihilation occur due to scattering? I think I'm confused on that terminology.

Thanks!!

Related High Energy, Nuclear, Particle Physics News on Phys.org

I know, but I can't find any information on if it's been done before.

I know, but I can't find any information on if it's been done before.
in high e+e- collisions one produces quark- antiquark pais, which hadronizes. The probability that only a proton and an antiproton is produced is close to 0 since they consists together of 3 valance quarks and of equal flavour.

I know, but I can't find any information on if it's been done before.
Yes, protons are among the measured products in high energy electron-positron collisions. An internet search shows, for example, the DELPHI experiment at LEP that among other things measured identified hadrons (including protons):

http://delphiwww.cern.ch/

The leading factor in the cross section for electron-positron (pair) production by photons (electromagnetic) is

σ0 = (1/137) (e2/mec2)2 = 0.58 x 10-27 cm2 = 0.58 millibarns

where me is the electron mass, so by substuting the proton mass Mp, the cross section for pbar-p (proton anti-proton) production in electron positron collisions is probably down by 18362, so

σ0 = ~2 x 10-34 cm2 = 200 picobarns for pbar-p production,

at collision energies well above 2 GeV (threshold to produce one p and one p-bar) in the center of mass. Equation 37.3 in

http://pdg.lbl.gov/2002/kinemarpp.pdf

gives the transformation from the energy in the lab frame to the energy in the center of mass frame.

Bob S

[added] The above very crude pbar-p production cross section estimate is probably missing an extra factor of 1/137. Also see page 10 of

http://moriond.in2p3.fr/QCD/2003/monday/Lin.pdf

for differential pbar-p cross section yields (units in picobarns) in the L3 CERN-LEP experiment.

Last edited:
what is position of the electron in the both magnetic field and elect. fild will be parellel ?