<IMG SRC="navi.gif" WIDTH=160 HEIGHT=440 usemap="#navi" BORDER=0> What is the World Made of?     Lepton Decay Quiz

Which lepton decays are possible? Why or why not?


(A tau lepton decays into an electron, an electron antineutrino, and a tau neutrino.)

Answer

Yes! Charge, tau number, electron number, and energy are all conserved.


(A tau lepton decays into a muon and a tau neutrino.)

Answer

No! Muon number is not conserved. A muon has a muon number of 1, and thus the right side of the decay equation has muon number 1, but the left side has muon number of 0.

Now try a tricky one:


(An electron decays into a muon, a muon antineutrino, and an electron neutrino.)

Answer

No! Surprise! Although electron and muon numbers are both conserved, energy is not conserved. A muon has a lot more mass than an electron, and a lepton cannot decay into something more massive than it started out!