Open-charm tetraquark $X_c$ and open-bottom tetraquark $X_b$

Motivated by the LHCb observation of exotic states $X_{0,1}(2900)$ with four open quark flavors in the $D^- K^+$ invariant mass distribution in the decay channel $B^\pm \to D^+ D^- K^\pm$, we study the spectrum and decay properties of the open charm tetraquarks. Using the two-body chromomagnetic interactions, we find that the two newly observed states can be interpreted as a radial excited tetraquark with $J^P=0^+$ and an orbitally excited tetraquark with $J^P=1^-$, respectively. We then explore the mass and decays of the other flavor-open tetraquarks made of $su \bar d \bar c$ and $d s \bar u \bar c$, which are in the $\bar 6$ or $15$ representation of the flavor SU(3) group. We point that these two states can be found through the decays: $X^{(\prime)}_{d s \bar{u}\bar{c}}\to (D^- K^-, D_s^- \pi ^-)$, and $X^{(\prime)}_{s u \bar{d}\bar{c}}\to D_s^-\pi ^+$. We also apply our analysis to open bottom tetraquark $X_b$ and predict their masses. The open-flavored $X_b$ can be discovered through the following decays: $X_{ud\bar s\bar{b}}\to B^0K^+$, $X^{(\prime)}_{d s \bar{u}\bar{b}}\to (B^0 K^-, B_s^0 \pi ^-)$, and $X^{(\prime)}_{s u \bar{d}\bar{b}}\to B_s^0\pi ^+$.