Variation of the relative yield of charged and neutral B mesons across the Upsilon(4S) resonance

It is shown that the ratio of the production rates of the pairs (B+ B-) and (B0 anti-B0) should experience a substantial and rapid variation with energy within the width of the Upsilon(4S) resonance, crossing the value of one near the center of the resonance. This behavior is due to an interference of the rapidly changing with energy Breit-Wigner phase with the phase introduced in the wave function of charged mesons by their Coulomb interaction.