A bstract Using data samples collected by the Belle and Belle II experiments at the Υ (4 S) resonance with integrated luminosities of 571 fb − 1 and 365 fb − 1, respectively, we measure the pseudoscalar B -meson mass difference to be m (B 0) − m (B +) = (0. 495 ± 0. 024 ± 0. 005) MeV/ c 2. The results are based on a simultaneous fit to the variable M ₁₂, which is related to the B momentum, for B 0 and B + candidates; and to the energy dependence of R= (e^+e^- B^0B ^0) / (e^+e^- B^+B^-), which is measured using changes in the average center-of-mass energy over the data taking periods. The phase-space hypothesis R= ({p₁^{0} /p₁^{+}) }^3, upon which previous measurements rely, is strongly disfavored by our fit; the measured mass-difference value for the phase-space hypothesis also differs significantly from our measurement. We constrain R in a broader energy range than covered by the direct measurement and extract the energy dependence of R in the range from the BB threshold up to 10. 59 GeV. We interpret the results using a phenomenological model and constrain the parameters of the BB potential in the isovector channel.
Abumusabh et al. (Fri,) studied this question.