Low-mass enhancement of kaon pairs in $B^{+}\to {\bar{D}}^{(\ast )0}{K}^{+}{\bar{K}}^0$ and $B^0\to D^{(\ast )-}{K}^{+}{\bar{K}}^0$ decays

Abstract

Very recently, the Belle~II Collaboration presented a measurement for the decays $B^{+}\to {\bar{D}}^{(\ast )0}{K}^{+}{\bar{K}}^0$ and $B^0\to D^{(\ast )-}{K}^{+}{\bar{K}}^0$, the bulk of observed $m(K^{+}{K}_S^0)$ distributions showing low-mass structures in all four channels. In this work, we study the contributions of $\ddot{I}(770,1450{)}^{+}$, $a_2(1320{)}^{+}$ and $a_0(980,1450{)}^{+}$ resonances to these decay processes. The intermediate states $\ddot{I}(770,1450{)}^{+}$ 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 $a_2(1320{)}^{+}$ meson is found to be negligible. Near the threshold of the kaon pair, the state $a_0(980{)}^{+}$ 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 $B^{+}\to {\bar{D}}^{(\ast )0}{K}^{+}{\bar{K}}^0$ 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 $K^{+}{\bar{K}}^0$ pairs near their threshold in these decay processes.

18 pages, 4 figures