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Very recently, the Belle~II Collaboration presented a measurement for the decays B^+^ (*) 0 K^+K⁰ and B⁰ D^ (*) -K^+K⁰, the bulk of observed m (K^+ KS⁰) distributions showing low-mass structures in all four channels. In this work, we study the contributions of (770, 1450) ^+, a₂ (1320) ^+ and a₀ (980, 1450) ^+ resonances to these decay processes. The intermediate states (770, 1450) ^+ are found to dominate the low-mass distribution of kaon pairs roughly contributing to half of the total branching fraction in each of the four decay channels. The contribution of the tensor a₂ (1320) ^+ meson is found to be negligible. Near the threshold of the kaon pair, the state a₀ (980) ^+ turns out to be much less important than expected, not being able to account for the enhancement of events in that energy region observed in the B^+^ (*) 0 K^+K⁰ decays. Further studies both from the theoretical and experimental sides are needed to elucidate the role of the non-resonant contributions governing the formation of K^+K⁰ pairs near their threshold in these decay processes.
Wang et al. (Tue,) studied this question.