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} $.