The Standard Model - What is the world made of? - Lepton decay quiz
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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!
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