Detailed Lattice-QCD Study for the Three-Quark Potential and Y-type Flux-Tube Formation

We study the ground-state three-quark (3Q) potential $V_{\rm 3Q}^{\rm g.s.}$ and the excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$ using SU(3) lattice Q CD. From the accurate and thorough calculation for more than 300 different patterns of 3Q systems, the static ground-state 3Q potential $V_{\rm 3Q}^{\rm g.s.}$ is found to be well described by the Coulomb plus Y-type linear potential, i.e., Y-ansatz, within 1%-level deviation. With lattice QCD, we calculate also the excited-state potential in the 3Q system, and find the gluonic excitation energy, $V_{\rm 3Q}^{\rm e.s.}-V_{\rm 3Q}^{\rm g.s.}$, to be about 1 GeV. This large gluonic-excitation energy would play an essential role to the success of the quark model for the low-lying hadrons in terms of the absence of the gluonic mode.