The muon family number is Lμ = 0 before and Lμ = −1+1 = 0 after. Strangeness changes from +1 before to 0 + 0 after, for an allowed change of 1. The decay is allowed by all these measures.
What particles have strangeness?
The strangeness of a particle is the sum of the strangeness of its component quarks. Of the six flavors of quarks, only the strange quark has a nonzero strangeness. The strangeness of nucleons is zero, because they only contain up and down quarks and no strange (also called sideways) quarks.
What is the strangeness of a muon?
The muon family number is Lμ = 0 before and Lμ = −1+1 = 0 after. Strangeness changes from +1 before to 0 + 0 after, for an allowed change of 1. The decay is allowed by all these measures.
