End point of the first-order phase transition of QCD in the heavy quark region by reweighting from quenched QCD

We study the end point of the first-order deconfinement phase transition in two- and 2 + 1 -flavor QCD in the heavy quark region of the quark mass parameter space. We determine the location of the critical point at which the first-order deconfinement phase transition changes to a crossover, and calculate the pseudoscalar meson mass at the critical point. Performing quenched QCD simulations on lattices with the temporal extents Nt = 6 and 8, the effects of heavy quarks are determined using the reweighting method. We adopt the hopping parameter expansion to evaluate the quark determinants in the reweighting factor. We estimate the truncation error of the hopping parameter expansion by comparing the results of leading- and next-to-leading-order calculations, and study the lattice spacing dependence as well as the spatial volume dependence of the result for the critical point. The overlap problem of the reweighting method is also examined. Our results for Nt = 4 and 6 suggest that the critical quark mass decreases as the lattice spacing decreases and increases as the spatial volume increases.