Four-Quark Mesons?

Using the LAMP model for nuclear quark structure, we calculate the binding energy and quark structure of a $B$ meson with a $D$ meson. The larger-than-nucleon masses of the two heavy quarks and the complete absence of quark Pauli Exclusion Principle repulsive effects produce a bound state with structure ranging from a deuteron-like state to a fully mixed four-quark state. Unlike the deuteron, however, pion exchange does not provide the dominant contribution to binding.