Antiheavy-Antiheavy-Light-Light Four-Quark Bound States

We present our recent results on antiheavy-antiheavy-light-light tetraquark systems using lattice QCD. Our study of the $\bar{b}\bar{b}us$ four-quark system with quantum numbers $J^P=1^+$ and the $\bar{b}\bar{c}ud$ four-quark systems with $I(J^P)=0(0^+)$ and $I(J^P)=0(1^+)$ utilizes scattering operators at the sink to improve the extraction of the low-lying energy levels. We found a bound state for $\bar{b}\bar{b}us$ with $E_{\textrm{bind},\bar{b}\bar{b}us} = (-86 \pm 22 \pm 10)\,\textrm{MeV}$, but no indication for a bound state in both $\bar{b}\bar{c}ud$ channels. Moreover, we show preliminary results for $\bar{b}\bar{b}ud$ with $I(J^P)=0(1^+)$, where we used scattering operators both at the sink and the source. We found a bound state and determined its infinite-volume binding energy with a scattering analysis, resulting in $E_{\textrm{bind},\bar{b}\bar{b}ud} =(-103 \pm 8 )\,\textrm{MeV}$.