We report on our progress with the ongoing study of exotic, heavy tetraquark states, $qq’ \bar Q\bar Q’$. With regards to the previously reported $\bar Q\bar Q’=\bar b\bar b$ case, we have significantly increased our statistics by computing and saving more propagators on publicly available dynamical $n_f =2+1$ Wilson-Clover gauge configurations, generated by the PACS-CS collaboration, with pion masses $\simeq$164, 299 and 415 MeV. We extend our previous analysis to heavy quark components containing heavier than physical bottom quarks $\bar Q\bar Q’=\bar b’\bar b’$, charm and bottom quarks $\bar c\bar b$ and also only charm quarks $\bar c\bar c$. Throughout we employ NRQCD and Fermilab heavy quarks for the heavier than bottom, bottom and charm quarks. Using our previously established diquark-antidiquark and meson-meson operator basis we comment in particular on the dependence of the binding energy on the mass of the heavy quark component $\bar Q\bar Q$, with heavy quarks ranging from $m_Q=0.7…6.3\cdot m_b$. In the heavy flavor non-degenerate case, $\bar Q\bar Q’$, and especially for the tetraquark channel $ud\bar c\bar b$, we extend our work to utilize a $3\times 3$ GEVP to study the ground and threshold states, thereby enabling an identification also of finite volume effects in this channel. Finally, we present some initial work on the $\bar Q\bar Q’=\bar c\bar c$ system where a much larger operator basis is available in comparison to flavor combinations with NRQCD quarks.

Hadron Spectroscopy and Interactions