First exotic hadron with open heavy flavor: $cs\bar{u}\bar{d}$ tetraquark

Abstract

The LHCb Collaboration has reported resonant activity in the channel $D^{+}{K}^{-}$, identifying two components: $X_0(2900)$ with $J^P=0^{+}$ at $2866\pm 7$ MeV, ${\Gamma }_0=57\pm 13$ MeV and $X_1(2900)$ with $J^P=1^{-}$ at $2904\pm 7$ MeV, ${\Gamma }_1=110\pm 12$ MeV. We interpret the $X_0(2900)$ component as a $cs\bar{u}\bar{d}$ isosinglet compact tetraquark, calculating its mass to be $2863\pm 12$ MeV. This is the first exotic hadron with open heavy flavor. The analogous $bs\bar{u}\bar{d}$ tetraquark is predicted at $6213\pm 12$ MeV. We discuss possible interpretations of the heavier and wider $X_1(2900)$ state and examine potential implications for other systems with two heavy quarks.

Comments: 4 pages, 1 figure; some additional physics comments; added references