Speaker
Description
The doubly bottom tetraquark $T_{bb}$, with $I(J^P) = 0(1^+)$, is widely expected to be a deeply bound exotic state. In contrast, much less is known about $BB^*$ scattering near and above threshold. Studying this system is challenging: one must separate the deeply bound $T_{bb}$ from the $B^{(*)}B^*$ scattering states by using both local tetraquark operators and bilocal scattering operators. In this exploratory study, we employed a relativistic heavy quark (RHQ) action for the $b$ quark on two CLS ensembles with Wilson-clover fermions at the $SU(3)$-flavour-symmetric point. To include both operator types in the variational analysis, we used the distillation framework combined with a position-space sampling method [arXiv:2510.26459]. In our preliminary analysis, we find a binding energy of about 50–60 MeV for the $T_{bb}$, consistent with the literature. We further determine the $s$-wave $BB^*$ scattering phase shift using Lüscher's finite-volume quantization conditions. The scattering amplitude from our single-channel analysis contains a pole close to threshold, indicating a shallow virtual bound state alongside the deeply bound $T_{bb}$.