Positron - electron annihilation.

JZR

Here is an excerpt from my textbook:

"The mass of a Z boson is about 90 Gev. By selecting the energy of the electron and positron beams in the LEP collider to be 45 Gev each, a high rate was achieved for the production of neutrino-antineutrino pairs in the process. The experiment shows that there are no more types of neutrino than the three already discovered. Had there been a fourth type of neutrino, the rate of electron-positron annihilation would have been higher than observed."

My question is, why would the rate of annihilation be higher if there were four types of neutrino?

betel

Basically you would have more possible channels in which your electron and positron can decay to. Providing more options for a decay will increase the rate.

phyzguy

Here's a nice explanation, with a graph:

http://backreaction.blogspot.com/200...-families.html