Finite-size scaling around the critical point in the heavy quark region of QCD

Finite-size scaling is investigated in detail around the critical point in the heavy quark region of nonzero temperature QCD. Numerical simulations are performed with large spatial volumes up to the aspect ratio Ns/Nt = 12 at a fixed lattice spacing with Nt = 4. We show that the Binder cumulant and the distribution function of the Polyakov loop follow the finite-size scaling in the Z(2) universality class for large spatial volumes with Ns/Nt >= 9, while, for Ns/Nt <= 8, the Binder cumulant becomes inconsistent with the Z(2) scaling. To realize the large-volume simulations in the heavy quark region, we adopt the hopping parameter expansion for the quark determinant: We generate gauge configurations using the leading-order action including the Polyakov loop term for Nt = 4, and incorporate the next-to-leading order effects in the measurements by the multipoint-reweighting method. We find that the use of the leading-order configurations is crucially effective in suppressing the overlapping problem in the reweighting and thus in reducing the statistical errors.