H Saito

Publications (8)0 Total impact

• Article: Probability distribution functions in the finite density lattice QCD

  S. Ejiri, Y. Nakagawa, S. Aoki, K. Kanaya, H. Saito, T. Hatsuda, H. Ohno, T. Umeda
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  ABSTRACT: We study the phase structure of QCD at high temperature and density by lattice QCD simulations adopting a histogram method. We try to solve the problems which arise in the numerical study of the finite density QCD, focusing on the probability distribution function (histogram). As a first step, we investigate the quark mass dependence and the chemical potential dependence of the probability distribution function as a function of the Polyakov loop when all quark masses are sufficiently large, and study the properties of the distribution function. The effect from the complex phase of the quark determinant is estimated explicitly. The shape of the distribution function changes with the quark mass and the chemical potential. Through the shape of the distribution, the critical surface which separates the first order transition and crossover regions in the heavy quark region is determined for the 2+1-flavor case.
  12/2012;
• Source

  Available from: Hiroshi Ohno

  Article: Histogram method in finite density QCD with phase quenched simulations

  Y. Nakagawa, S. Ejiri, S. Aoki, K. Kanaya, H. Ohno, H. Saito, T. Hatsuda, T. Umeda
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  ABSTRACT: We propose a new approach to finite density QCD based on a histogram method with phase quenched simulations at finite chemical potential. Integrating numerically the derivatives of the logarithm of the quark determinant with respect to the chemical potential, we calculate the reweighting factor and the complex phase of the quark determinant. The complex phase is handled with a cumulant expansion to avoid the sign problem. We examine the applicability of this method.
  11/2011;
• Source

  Available from: Yu Maezawa

  Article: Phase structure of finite temperature QCD in the heavy quark region

  H. Saito, S. Ejiri, S. Aoki, T. Hatsuda, K. Kanaya, Y. Maezawa, H. Ohno, T. Umeda
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  ABSTRACT: We study the quark mass dependence of the finite temperature QCD phase transition in the heavy quark region using an effective potential defined through the probability distribution function of the average plaquette. Performing a simulation of SU(3) pure gauge theory, we first confirm that the distribution function has two peaks indicating that the phase transition is of first order in the heavy quark limit, while the first order transition turns into a crossover as the quark mass decreases from infinity, where the mass dependence of the distribution function is evaluated by the reweighting method combined with the hopping parameter expansion. We determine the endpoint of the first order transition region for N_f=1, 2, 3 and 2+1 cases. The quark mass dependence of the latent heat is also evaluated in the first order transition region.
  06/2011;
• Source

  Available from: Yu Maezawa

  Article: Charmonium spectral functions with the variational method in zero and finite temperature lattice QCD

  H. Ohno, S Aoki, S. Ejiri, K. Kanaya, Y. Maezawa, H Saito, T Umeda
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  ABSTRACT: We propose a method to evaluate spectral functions on the lattice based on a variational method. On a lattice with a finite spatial extent, spectral functions consist of discrete spectra only. Adopting a variational method, we calculate the locations and the heights of spectral functions at low-lying discrete spectra. We first test the method in the case of analytically solvable free Wilson quarks at zero and finite temperatures and confirm that the method well reproduces the analytic results for low-lying spectra. We find that we can systematically improve the results by increasing the number of trial states. We then apply the method to calculate the charmonium spectral functions for S and P-wave states at zero-temperature in quenched QCD and compare the results with those obtained using the conventional maximum entropy method (MEM). The results for the ground state are consistent with the location and the area of the first peak in spectral functions from the MEM, while the variational method leads to a mass which is closer to the experimental value for the first excited state. We also investigate the temperature dependence of the spectral functions for S-wave states below and above $T_c$. We obtain no clear evidences for dissociation of $J/\psi$ and $\eta_c$ up to 1.4$T_c$.
  04/2011;
• Source

  Available from: Yu Maezawa

  Article: Scaling behavior of chiral phase transition in two-flavor QCD with improved Wilson quarks at finite density

  S. Ejiri, Y Nakagawa, S Aoki, K. Kanaya, H. Ohno, H Saito, T. Hatsuda, Y. Maezawa, T Umeda
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  ABSTRACT: We study scaling behavior of a chiral order parameter performing a simulation of two-flavor QCD with improved Wilson quarks. It has been shown that the scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Calculating derivatives of the chiral order parameter with respect to the chemical potential in two-flavor QCD, the scaling property of chiral phase transition is discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chirl phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation.
  01/2011;
• Source

  Available from: Yu Maezawa

  Article: The order of the deconfinement phase transition in a heavy quark mass region

  H Saito, S Aoki, K. Kanaya, H. Ohno, S. Ejiri, T. Hatsuda, Y. Maezawa, T Umeda
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  ABSTRACT: We study the quark mass dependence of the QCD phase transition by an effective potential defined through the distribution function of observables. As a test of the method, we study the first order deconfinement phase transition in the heavy quark mass limit and its fate at lighter quark masses. We confirm that the distribution function for the plaquette has two peaks indicating that the phase transition is of first order in the heavy quark limit. We then study the quark mass dependence of the distribution function by a reweighting method combined with the hopping parameter expansion. We find that the first order transition turns into a crossover as the quark mass decreases. We determine the critical point for the cases of $N_f$=1, 2, 3 and 2+1. We find that the probability distribution function provides us with a powerful tool to study the order of transitions. Comment: 7 pages, 7 figure, Talk presented at the XXVIII International Symposium on Lattice Field Theory, Lattice2010, Villasimius, Italy, June 2010
  11/2010;
• Source

  Available from: Yu Maezawa

  Article: An application of the variational analysis to calculate the meson spectral functions

  H. Ohno, S Aoki, S. Ejiri, K. Kanaya, Y. Maezawa, H Saito, T Umeda
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  ABSTRACT: We present a new method to calculate meson spectral functions (SPFs) on the lattice based on a variational method. Because, on a finite volume lattice, the meson SPFs have discrete spectra only, a suitable way to extract such discrete signals is needed. Using a variational method, we can calculate several discrete quantities such as the position and the area of spectral peaks for low-lying states. Moreover data accuracy can be improved by increasing the number of basis functions. In this report, we first confirm our method in the free quark case and show that our method works well. Then, we apply the method to a quenched lattice QCD simulation and calculate the charmonium SPFs for S and P-waves at zero temperature. Our results for the ground state are well consistent with the position and the area of the lowest peaks of charmonium SPFs calculated by the conventional maximum entropy method. For first excited states, the signals may be reliablly extracted with our method because the charmonium mass converges to a value close to the experimental one when the number of basis functions is increased. We also investigate the SPFs for S-wave charmonia at below and above $T_c$. Our results suggest that $J/\psi$ and $\eta_c$ may survive up to 1.4$T_c$.
  11/2010;
• Source

  Available from: Yu Maezawa

  Article: QCD thermodynamics at zero and finite densities with improved Wilson quarks

  K. Kanaya, S Aoki, S. Ejiri, T. Hatsuda, N Ishii, Y. Maezawa, H. Ohno, H Saito, N. Ukita, T Umeda
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  ABSTRACT: The WHOT-QCD Collaboration is pushing forward lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. We first present results on QCD at zero and finite densities with two flavors of degenerate quarks (N_F=2 QCD) adopting the conventional fixed-Nt approach. We then report on the status of a study of N_F=2+1 QCD adopting a fixed-scale approach armed with the T-integration method which we have developed.
  08/2010;