# History of High Energy electron-positron collisions

by dseabroo
Tags: collisions, electronpositron, energy, history
 P: 6 Can someone please tell me the history of high-energy electron-positron collisions? In specific when was it discovered that such collisions can create hadrons? Any information would be useful. Thanks.
 P: 986 According to Wikipedia, the first electron-positron collider was called AdA, it was constructed in Italy in the early 60's. Its energy and luminosity were insufficient to observe hadron production. Soviet collider called VEPP-2 was launched in Novosibirsk in 1966. They were the ones who first observed pion pair production in in e+e- collisions in 1967. By the early 70's, Americans got seriously involved too, SLAC in Stanford was up and running by 1972 and made a couple of major discoveries in 1974-76. http://accelconf.web.cern.ch/AccelCo...C1973_0756.PDF That does not answer your exact question - when was it discovered that you could make hadrons in electron-positron collisions - because, even before these colliders went online, physicists knew that you could produce pion pairs that way, and they were even able to estimate production cross sections. How they got there, I don't know, maybe it involved observing cosmic ray positrons somehow.
P: 1,160
 Quote by hamster143 That does not answer your exact question - when was it discovered that you could make hadrons in electron-positron collisions - because, even before these colliders went online, physicists knew that you could produce pion pairs that way, and they were even able to estimate production cross sections. How they got there, I don't know, maybe it involved observing cosmic ray positrons somehow.
The hadron pair production e-+e+ → h-+h+ can be considered and calculated as a cross channel of the known elastic electron scattering off hadrons e-+h+ → e-+h+.

Bob_for_short.

P: 986

## History of High Energy electron-positron collisions

 Quote by Bob_for_short The hadron pair production e-+e+ → h-+h+ can be considered and calculated as a cross channel of the known elastic electron scattering off hadrons e-+h+ → e-+h+. Bob_for_short.

That is a good point - crossing symmetry was already known in the 60's. Regarding the cross process, to get pion and kaon pair production amplitudes, physicists must have measured pion scattering on electrons, not vice versa.
 P: 6 Thanks for your quick reply guys. A few more questions: In addition to creation via collisions are you aware of any other way that hadrons come about. For instance do charged proton-anti-proton pairs appear, theoretically, in electric fields via the Schwinger Effect? If you would provide any citations to important papers about the creation of hadron pairs via Schwinger or electron-positron collisions I would be charmed. Any insight at all into hadron creation is welcome. Thanks again.
P: 986
 Quote by dseabroo Thanks for your quick reply guys. A few more questions: In addition to creation via collisions are you aware of any other way that hadrons come about. For instance do charged proton-anti-proton pairs appear, theoretically, in electric fields via the Schwinger Effect?
Theoretically yes, but electric fields required are immense. Even electron-positron pair production via Schwinger Effect has not been observed yet (to my knowledge) and energies required for pp are three orders of magnitude higher. There is potential to achieve those effects with high-powered lasers.

Most hadrons in the Universe came about through condensation of primordial quark-gluon plasma as it cooled shortly after the Big Bang.

 P: 986 First of all I must correct myself - the field for pp is not three but six orders of magnitude greater than the field for ee. And the field needed for ee pairs is on the order of 10^18 V/m. Below that, pair production is exponentially suppressed by a factor $$(E_{crit}/E)^2 exp(-E_{crit}/E)$$. You still see pairs, but, the lower the field, the less likely it is to create particle pairs. Already at the field 1% of critical the rate is so low that you're exceedingly unlikely to detect any pairs created during your lifetime. The field needed can be estimated by a simple semiclassical argument. In the vacuum, virtual particle pairs appear and disappear all the time. A typical separation between two particles in such a pair is on the order of their Compton wavelength. You will see significant pair production if the field is so strong that the difference of potentials over the Compton wavelength is comparable to the rest energy of the pair. If the field is strong enough, you will see ee pairs, pp pairs, all sorts of other pairs, muons, pions, etc. etc. The ratio of pp/ee in a strong enough field would probably be on the order of 1 - but protons and antiprotons are not elementary particles and the dynamic of their creation would be much more complicated. Also, there's a big assumption we're making, namely that it's even possible to sustain a field of that magnitude. A system with field strength above ee creation threshold would be constantly losing energy to pair creation.