We investigate the exotic hadrons consisting of two light quarks and two heavy antiquarks, $(q\bar Q)$-$(q\bar Q)$. The spin-dependent term between quarks is known to give an attraction to the $ud$ spin-0 component in the isospin-0 $u\bar c d\bar c$ system, $T_{ cc}$. However, the said component also gets a repulsion from the partial Pauli-blocking. By the dynamical calculation with a simplified quark model, we discuss that the competition of the two effects leads to a shallow bound state for $T_{ cc}$, which is preferred from the experiment, and a deep bound state for $T_{ bb}$.
Categories: hep-ph