First exotic hadron with open heavy flavor: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>c</mml:mi><mml:mi>s</mml:mi><mml:mover accent="true"><mml:mi>u</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mover accent="true"><mml:mi>d</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover></mml:math> tetraquark
Marek Karliner, Jonathan L. Rosner
Abstract
The LHCb Collaboration has reported resonant activity in the channel ${D}^{+}{K}^{\ensuremath{-}}$, identifying two components: ${X}_{0}(2900)$ with ${J}^{P}={0}^{+}$ at $2866\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{MeV}$, ${\mathrm{\ensuremath{\Gamma}}}_{0}=57\ifmmode\pm\else\textpm\fi{}13\text{ }\text{ }\mathrm{MeV}$ and ${X}_{1}(2900)$ with ${J}^{P}={1}^{\ensuremath{-}}$ at $2904\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{MeV}$, ${\mathrm{\ensuremath{\Gamma}}}_{1}=110\ifmmode\pm\else\textpm\fi{}12\text{ }\text{ }\mathrm{MeV}$. We interpret the ${X}_{0}(2900)$ component as a $cs\overline{u}\overline{d}$ isosinglet compact tetraquark, calculating its mass to be $2863\ifmmode\pm\else\textpm\fi{}12\text{ }\text{ }\mathrm{MeV}$. This is the first exotic hadron with open heavy flavor. The analogous $bs\overline{u}\overline{d}$ tetraquark is predicted at $6213\ifmmode\pm\else\textpm\fi{}12\text{ }\text{ }\mathrm{MeV}$. We discuss possible interpretations of the heavier and wider ${X}_{1}(2900)$ state and examine potential implications for other systems with two heavy quarks.