Phase structure of finite density QCD with a histogram method

(WHOT-QCD collaboration) We study the phase structure of QCD in the T − µ plane using a histogram method and the reweighting technique by performing phase quenched simulations of two-flavor QCD with RG-improved gauge action and O(a) improved Wilson quark action. Taking the effects of the complex phase of the quark determinant using the cumulant expansion method, we calculate the probability distribution function of plaquette and phase-quenched determinant as a function of T and µ. We discuss the order of the QCD phase transition consulting the shape of the probability distribution function