# Suppression of semileptonic lambda decays

• I
Confused by the branching ratio of uds ---> proton + e- + neutrino compared to uds ---> proton + pion (or neutron + pion).

In both cases an W boson is being produced as the strange quark changes flavour, and it is either decaying to leptons or first generation quarks - why is the leptonic decay so suppressed? (BR of order 10^-4).

I can see it must be easier to distribute momentum to two particles of similar mass, but is there a simple way to quantify this without doing the full phase space calculation?