Mixing of S-Wave Charmonia with $\mathrm{D}\overline{\mathrm{D}}$ Molecule States

Understand

Charmonium states can decay into pairs of $D$ and $\overline{D}$ mesons if their masses are above the allowed decay thresholds.

• In general $c\bar{c}$ states near threshold will also undergo mixing with $D\overline{D}$ molecular (or tetraquark) states, by creation and annihilation of light quark-antiquark pairs.
• The investigation of such effects sheds light on the higher Fock state contributions to charmonium wavefunctions and on mass shifts, relative to a scenario where such mixing effects are neglected.
• A variational approach is applied to a mixing matrix between operators of both sectors, of $c\bar{c}$ and of $D\overline{D}$ molecular type.