= Strangeness selection in pion-proton and kaon-proton resonances
The $\pi^+p$ channel has baryon number one, strangeness zero and $I_3=3/2$, matching the ordinary $uuu$ <Delta baryon>. The $K^+p$ channel has strangeness plus one, which no three-light-quark baryon can have because each strange quark contributes minus one. A resonance in that channel would require exotic content such as four quarks and an antiquark; the ordinary low-energy qqq multiplets therefore explain the contrast.
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