138 research outputs found
Study of QCD critical point using canonical ensemble method
The existence of the QCD critical point at non-zero baryon density is not
only of great interest for experimental physics but also a challenge for the
theory. We use lattice simulations based on the canonical ensemble method to
explore the finite baryon density region and look for the critical point. We
scan the phase diagram of QCD with three degenerate quark flavors using clover
fermions with on lattices. We measure the
baryon chemical potential as we increase the density and we see the
characteristic "S-shape" that signals the first order phase transition. We
determine the phase boundary by Maxwell construction and report our preliminary
results for the location of critical point.Comment: 2 pages, 2 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Critical point of QCD from lattice simulations in the canonical ensemble
A canonical ensemble algorithm is employed to study the phase diagram of QCD using lattice simulations. We lock in the desired quark number sector
using an exact Fourier transform of the fermion determinant. We scan the phase
space below and look for an S-shape structure in the chemical potential,
which signals the coexistence phase of a first order phase transition in finite
volume. Applying Maxwell construction, we determine the boundaries of the
coexistence phase at three temperatures and extrapolate them to locate the
critical point. Using an improved gauge action and improved Wilson fermions on
lattices with a spatial extent of 1.8 \fm and quark masses close to that of
the strange, we find the critical point at and baryon
chemical potential .Comment: 5 pages, 7 figures, references added, published versio
Non-perturbative renormalization of overlap quark bilinears on domain wall fermion configurations
We present renormalization constants of overlap quark bilinear operators on
2+1-flavor domain wall fermion configurations. Both overlap and domain wall
fermions have chiral symmetry on the lattice. The scale independent
renormalization constant for the local axial vector current is computed using a
Ward Identity. The renormalization constants for the scalar, pseudoscalar and
vector current are calculated in the RI-MOM scheme. Results in the MS-bar
scheme are obtained by using perturbative conversion ratios. The analysis uses
in total six ensembles with lattice sizes 24^3x64 and 32^3x64.Comment: 7 pages, 10 figures, presented at the 31st International Symposium on
Lattice Field Theory (LATTICE 2013), 29 July - 3 August 2013, Mainz, German
Non-perturbative renormalization of overlap quark bilinears on 2+1-flavor domain wall fermion configurations
We present renormalization constants of overlap quark bilinear operators on
2+1-flavor domain wall fermion configurations. This setup is being used by the
chiQCD collaboration in calculations of physical quantities such as strangeness
in the nucleon and the strange and charm quark masses. The scale independent
renormalization constant for the axial vector current is computed using the
Ward Identity. The renormalization constants for scalar, pseudoscalar and
vector current are calculated in the RI-MOM scheme. Results in the MS-bar
scheme are also given. The step scaling function of quark masses in the RI-MOM
scheme is computed as well. The analysis uses, in total, six different
ensembles of three sea quarks each on two lattices with sizes 24^3x64 and
32^3x64 at spacings a=(1.73 GeV)^{-1} and (2.28 GeV)^{-1}, respectively.Comment: 26 pages, 17 figures. More discussions on O(4) breaking effects, and
on the perturbative running and a^2p^2 extrapolation of Zs. A subsection for
the calculation of the step scaling function of quark mass is added.
References added. Version to appear in PR
Finite density phase transition of QCD with and using canonical ensemble method
In a progress toward searching for the QCD critical point, we study the
finite density phase transition of and 2 lattice QCD at finite
temperature with the canonical ensemble approach. We develop a winding number
expansion method to accurately project out the particle number from the fermion
determinant which greatly extends the applicable range of baryon number sectors
to make the study feasible. Our lattice simulation was carried out with the
clover fermions and improved gauge action. For a given temperature, we
calculate the baryon chemical potential from the canonical approach to look for
the mixed phase as a signal for the first order phase transition. In the case
of , we observe an "S-shape" structure in the chemical potential-density
plane due to the surface tension of the mixed phase in a finite volume which is
a signal for the first order phase transition. We use the Maxwell construction
to determine the phase boundaries for three temperatures below . The
intersecting point of the two extrapolated boundaries turns out to be at the
expected first order transition point at with . This serves as a
check for our method of identifying the critical point. We also studied the
case, but do not see a signal of the mixed phase for temperature as
low as 0.83 .Comment: 28 pages, 11 figures,references added, final versio
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