Charged-to-neutral heavy meson yield ratio at the Z_b⁰ resonances as a probe of the I^G(J^P)=0^-(1^+) channel

It is argued that the ratio of the yield of pairs of charged and neutral $B^{(*)}$ mesons in the processes $\Upsilon(5S) \to \pi^0 + (B \bar B^* + c.c.)$ and $\Upsilon(5S) \to \pi^0 + B^* \bar B^*$ is very sensitive near the corresponding heavy meson threshold to the strong interaction between the mesons in the $I^G(J^P)=0^-(1^+)$ channel due to significant isospin breaking by the Coulomb force. This channel, not readily accessible by other means, may contain near-threshold molecular meson-antimeson resonances --- isoscalar analogs of the isovector states $Z_b(10610)$ and $Z_b(10650)$.