Speaker
Description
We present two lattice studies: The $\bar bb\bar qq$ systems with various quantum numbers using static bottom quarks and $\bar cc \bar qq$ systems with $I(J^{PC})=1(1^{+\pm})$.
Only one set of quantum numbers that couples to $Z_b$ and $\Upsilon\;\pi$ was explored on the lattice before; these studies found an attractive potential between $B$ and $\bar B^*$ resulting in a bound state below the threshold. The first study ($\bar bb\bar qq$) considers the other three sets of quantum numbers. Eigen-energies are extracted as a function of separation between $b$ and $\bar b$. The resulting eigen-energies do not show any sizable deviation from noninteracting energies of the systems $\bar bb+\bar qq$ and $\bar bq+\bar qb$, so no significant attraction or repulsion is found.
Our second study ($\bar cc \bar qq$) is the first study for four-quark states with $I(J^{PC})=1(1^{+\pm})$, a non-zero total momentum and two different lattice volumes. Our preliminary lattice results show that the energy shifts for eigenstates dominated by $D\bar{D}^*$ are very small in the $1^{++}$ channel and consistent with zero in the $1^{+-}$ channel. Our future plan is to determine the scattering amplitude for the coupled $J/\psi\pi - D\bar{D}^*$ scattering close to the $D\bar{D}^*$ threshold that reproduces experimental results and lattice spectra.
