Compulsory Resonance Formation

It is noted that if two mesons are allowed by the quark model to resonate, they do so for $p^{*}\le p_0^{\mathrm{MM}}\equiv 350$ MeV/c, where $p^{*}$ is the c.m. momentum. The corresponding value for mesonbaryon systems is $p_0^{\mathrm{MB}}\equiv 250$ MeV/c, suggesting (in an optical picture) that the baryon is indeed bigger than the meson. Crucial tests of the rule are provided by exotic baryon-antibaryon systems, for which one expects $p_0^{\mathrm{BB}}\cong 200$ MeV/c, and by other specific two-body modes which are predicted to resonate not far above threshold.