The $X_0(2900)$ and its heavy quark spin partners in molecular picture

Abstract

The $X_0(2900)$ observed by the LHCb Collaboration recently in the $D^-K^+$ invariant mass of the $B^+\to D^+D^-K^+$ process is the first exotic candidate with four different flavors, which opens a new era for the hadron community. Under the assumption that the $X_0(2900)$ is a $I(J^P)=0(0^+)$ $\bar{D}^*K^*$ hadronic molecule, we extract the whole heavy-quark symmetry multiplet formed by the $\left(\bar{D},\bar{D}^*\right)$ doublet and the $K^*$ meson. For the bound state case, there would be two additional $I(J^P)=0(1^+)$ hadronic molecules associated with the $\bar{D}K^*$ and $\bar{D}^*K^*$ channels as well as one additional $I(J^P)=0(2^+)$ $\bar{D}^*K^*$ molecule. In the light quark limit, they are $36.66~\mathrm{MeV}$ and $34.22~\mathrm{MeV}$ below the $\bar{D}K^*$ and $\bar{D}^*K^*$ thresholds, respectively, which are unambiguously fixed by the mass position of the $X_0(2900)$. For the virtual state case, there would be one additional $I(J^P)=0(1^+)$ hadronic molecule strongly coupling to the $\bar{D}K^*$ channel and one additional $I(J^P)=0(2^+)$ $\bar{D}^*K^*$ molecule. Searching for these heavy quark spin partners will help shed light on the nature of the $X_0(2900)$.