Y-type flux-tube formation in baryons

For more than 300 different patterns of the 3Q systems, the ground-state 3Q potential V-3Q(g.s.), is investigated using SU(3) lattice QCD with 123 x 24 at beta = 5.7 and 16(3) x 32 at beta = 5.8, 6.0 at the quenched level. As a result of the detailed analyses, we find that the ground-state potential V-3Q(g.s.) is well described with so-called Y-ansatz as V-3Q = -A(3Q) Sigma(i < j) 1/vertical bar r(i) - r(j)vertical bar + sigma(3Q) L-min + C-3Q, with the accuracy better than 1%. Here, L in denotes the minimal value of total flux-tube length. We also study the excited-state potential V-3Q(e.s.) using lattice QCD with 16 x 32 at 0 = 5.8,6.0 for more than 100 patterns of the 3Q systems. The energy gap between V-3Q(e.s.) and V-3Q(e.s.) which physically means the gluonic excitation energy, is found to be about 1 GeV in the typical hadronic scale. Finally, we suggest a possible scenario which connects the success of the quark model to QCD.