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

TL;DR

This study investigates how S-wave charmonium states mix with D D̄ molecular states near threshold, revealing their impact on charmonium properties through lattice QCD calculations.

Contribution

It introduces a variational approach with all-to-all propagators to analyze mixing between charmonium and molecular states on the lattice.

Findings

Evidence of mixing effects near threshold

Mass shifts due to D D̄ molecular components

Enhanced understanding of charmonium wavefunctions

Abstract

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. The efficient calculation of several diagrams appearing in this matrix requires all-to-all propagators, which are realized by sophisticated stochastic estimator techniques. The runs are performed on $n_F=2$ $24^3\times 48$ lattice volumes with $m_{\pi} \approx 280$ MeV, using the non-perturbatively improved clover Wilson action, both for valence and for sea quarks.