Interquark potential for the charmonium system with almost physical quark masses

We study an interquark Q Q ¯ potential for the charmonium system, that is determined from the equal-time and Coulomb gauge Q Q ¯ Bethe–Salpeter (BS) wavefunction through the effective Schrödinger equation. This novel approach enables us to evaluate a kinetic heavy quark mass m Q and a proper interquark potential at finite quark mass m Q , which receives all orders of 1 / m Q corrections on the static Q Q ¯ potential from Wilson loops, simultaneously. Precise information of the interquark potential for both charmonium and bottomonium states directly from lattice QCD provides us a chance to improve quark potential models, where the spin-independent interquark potential is phenomenologically described by the Cornell potential and the spin-dependent parts are deduced within the framework of perturbative QCD, from first-principles calculations. In this study, calculations are carried out in both quenched and dynamical fermion simulations. We first demonstrate that the interquark potential at finite quark mass calculated by the BS amplitude method smoothly approaches the conventional static heavy quark potential from Wilson loops in the infinitely heavy quark limit within quenched lattice QCD simulations. Second, we determine both spin-independent and dependent parts of the interquark potential for the charmonium system in 2+1 flavor dynamical lattice QCD using the PACS-CS gauge configurations at the lightest pion mass, M π = 156  MeV.