Why do atmospheric pions decay to muons, not electrons?

[Kolahal Bhattacharya]

Why does pions(coming through atmosphere) decays into a muon and a muon neutrino, not directly into electron and lelectron neutrino?I know it's because splin angular momentum conservation...but I need to be more clear about it.

 

[Norman]

Actually some of the pions do decay directly into electron and anti-neutrino (or positron and neutrino). But the branching ratio for this process is very small- only about 1%.

To explain this, please read:http://hyperphysics.phy-astr.gsu.edu/hbase/particles/hadron.html"

And Griffiths' book on particle physics also has a very good discussion.

Cheers.