We study the color correlation between two static quarks in 3Q ($QQQ$) and 4Q ($QQ\overline{Q}\overline{Q}$) multiquark systems at $T=0$ based on the reduced two-body density matrices $\rho$ in color space. We perform quenched lattice QCD calculations with the Coulomb gauge adopting the standard Wilson gauge action, and the spatial volume is $L^3=32^3$ at $\beta =5.8$, which corresponds to the lattice spacing $a=0.14\mathrm{fm}$ and the system volume $L^3={4.5}^3{\mathrm{fm}}^3$. We evaluate the two-body color density matrix $\rho$ of static quarks and investigate the dependence of color correlations on the quarks’ spatial configuration. As a result, we find that the color correlations depend on the minimal path length along a flux tube which connects two quarks under consideration. The color correlation between quarks quenches because of color leak into the gluon field (flux tube) and the color configuration of quarks finally approaches the random one in the large distance limit. We also find a “universality” in the flux-tube path length dependence of the color correlations for 2Q, 3Q, and 4Q ground-state systems. Our results show that the color correlations of end-point quarks can be a clue to clarify the internal structures of hadrons, including exotic (multiquark) hadrons.

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• Color confinement
• Lattice gauge theory
• Non-Abelian gauge theories
• Quantum chromodynamics