Searching for evidence of diquark states using lattice QCD simulations

In recent years, exotic hadrons called X, Y, Z which cannot be explained by the quark model have been found one after another. The tetra–quark state, which is one of the typical scenarios to interpret the exotic state, is based on the existence of a diquark state. The discovery of a pentaquark state at CERN in 2015 also makes a diquark state even more important. Therefore, it is considered that a diquark state plays an important role in many kinds of QCD physics. We discuss existence of such diquarks from the viewpoint of a first principle calculation.