Grading a problem set

PHYSICS · Subjective · Fermi University Physics · Particle Physics & Quantum Fields · Particles, interactions and experiment · Particles, interactions and experiment

Particle Physics, Ch Quantum numbers, conservation laws and allowed reactions

Problem

Grading a problem set, a marker writes: "For the reaction K+→π++π0K^+ \to \pi^+ + \pi^0, strangeness gives S=+1S=+1 on the left (K+=usˉK^+=u\bar s) and S=0S=0 on the right, since neither pion carries a strange quark. Since strangeness is not conserved, this decay is forbidden." Find the error in this reasoning, and state whether K+→π++π0K^+ \to \pi^+ + \pi^0 is in fact observed.

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