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How to make sense of a kaon decay $$K^+ \to \pi^0 + e^+ + \nu_e$$ if we take into account the quark structure of the kaon $K^+ = u \bar{s}$ and pion $\pi^0 = (u \bar{u} - d \bar{d})/\sqrt{2}$? Obviously, we have the weak decay of the $\bar{s}$ quark which produces $\bar{u}$. But, how do we get the extra $d \bar{d}$ quarks?

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The notation $\pi^0 = (u\bar{u} - d\bar{d})/\sqrt{2}$ means that the $\pi^0$ has equal probability of being either $u\bar{u}$ or $d\bar{d}$. It definitely doesn't mean they're tetraquarks!

They can be formed from a $u\bar{u}$ pair without having to consider the possibility of $d\bar{d}$, and vice-versa.

dukwon
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