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Z. Fodor

Publications and source records attributed to Z. Fodor.

At least 145 records · Page 8Linked to original sources
arXiv2009

The curvature of the QCD phase transition line

We determine the curvature of the phase transition line in the mu-T plane through an analysis of various observables, including the Polyakov loop, the quark number susceptibilities and the susceptibility of the chiral condensate. The second derivative of these quantities with respect to mu was calculated. The measurements were carried out on N_T = 4,6,8 and 10 lattices generated with a Symanzik improved gauge and stout-link improved 2+1 flavour staggered fermion action using physical quark masses.

hep-lat↗
arXiv2009

Scaling study of dynamical smeared-link clover fermions

We present a framework for phenomenological lattice QCD calculations which makes use of a tree level Symanzink improved action for gluons and stout-link Wilson fermions. We give details of our efficient HMC/RHMC algorithm and present a scaling study of the low-lying N_f=3 baryon spectrum. We find a scaling region that extends to a~<0.16fm and conclude that our action and algorithm are suitable for large scale phenomenological investigations of N_f=2+1 QCD. We expect this conclusion to hold for other comparable actions.

hep-lat↗
arXiv2008

Energy dependence of phi meson production in central Pb+Pb collisions at sqrt(s_nn) = 6 to 17 GeV

Phi meson production is studied by the NA49 Collaboration in central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV beam energy. The data are compared with measurements at lower and higher energies and to microscopic and thermal models. The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.

nucl-ex↗
arXiv2008

Status of the QPACE Project

We give an overview of the QPACE project, which is pursuing the development of a massively parallel, scalable supercomputer for LQCD. The machine is a three-dimensional torus of identical processing nodes, based on the PowerXCell 8i processor. The nodes are connected by an FPGA-based, application-optimized network processor attached to the PowerXCell 8i processor. We present a performance analysis of lattice QCD codes on QPACE and corresponding hardware benchmarks.

hep-lat↗
arXiv2008

Event-by-event transverse momentum fluctuations in nuclear collisions at CERN SPS

The latest NA49 results on event-by-event transverse momentum fluctuations are presented for central Pb+Pb interactions over the whole SPS energy range (20A - 158A GeV). Two different methods are applied: evaluating the $Φ_{p_{T}}$ fluctuation measure and studying two-particle transverse momentum correlations. The obtained results are compared to predictions of the UrQMD model. The results on the energy dependence are compared to the NA49 data on the system size dependence. The NA61 (SHINE, NA49-future) strategy of searching of the QCD critical end-point is also discussed.

nucl-ex↗
arXiv2007

Recent Result in QCD Thermodynamics from the Lattice

Recent results on QCD thermodynamics are presented. The nature of the T>0 transition is determined, which turns out to be an analytic cross-over. The absolute scale for this transition is calculated. The results were obtained by using a Symanzik improved gauge and stout-link improved fermionic action. In order to approach the continuum limit four different sets of lattice spacings were used with temporal extensions N_t=4, 6, 8 and 10 (they correspond to lattice spacings a \sim 0.3, 0.2, 0.15 and 0.12 fm). The equation of state is determined on N_t=4 and 6 lattices. The importance of the continuum limit for different results (critical endpoint, colour superconducting phase) at non-vanishing baryonic densities is discussed.

hep-lat↗
arXiv2007

QCD Thermodynamics

Recent results on QCD thermodynamics are presented. The nature of the T>0 transition is determined, which turns out to be an analytic cross-over. The absolute scale for this transition is calculated. The temperature dependent static potential is given. The results were obtained by using a Symanzik improved gauge and stout-link improved fermionic action. In order to approach the continuum limit four different sets of lattice spacings were used with temporal extensions N_t=4, 6, 8 and 10 (they correspond to lattice spacings a \sim 0.3, 0.2, 0.15 and 0.12 fm). A new technique is presented, which --in contrast to earlier methods-- enables one to determine the equation of state at very large temperatures.

hep-lat↗
arXiv2007

Chiral behavior of pseudo-Goldstone boson masses and decay constants in 2+1 flavor QCD

We present preliminary results for the chiral behavior of charged pseudo-Goldstone-boson masses and decay constants. These are obtained in simulations with N_f=2+1 flavors of tree-level, O(a)-improved Wilson sea quarks. In these simulations, mesons are composed of either valence quarks discretized in the same way as the sea quarks (unitary simulations) or of overlap valence quarks (mixed-action simulations). We find that the chiral behavior of the pseudoscalar meson masses in the mixed-action calculations cannot be explained with continuum, partially-quenched chiral perturbation theory. We show that the inclusion of O(a^2) unitarity violations in the chiral expansion resolves this discrepancy and that the size of the unitarity violations required are consistent with those which we observe in the zero-momentum, scalar-isotriplet-meson propagator.

hep-lat↗
arXiv2007

Static quark free energies at finite temperature

We determine the static quark free energies around the transition temperature using 2+1 flavors of staggered fermions. Simulations are carried out on N_t=4,6,8 and 10 lattices using physical quark masses. The free energies extracted from Polyakov-loop correlators are extrapolated to the continuum limit.

hep-lat↗
arXiv2007

QCD on the Cell Broadband Engine

We evaluate IBM's Enhanced Cell Broadband Engine (BE) as a possible building block of a new generation of lattice QCD machines. The Enhanced Cell BE will provide full support of double-precision floating-point arithmetics, including IEEE-compliant rounding. We have developed a performance model and applied it to relevant lattice QCD kernels. The performance estimates are supported by micro- and application-benchmarks that have been obtained on currently available Cell BE-based computers, such as IBM QS20 blades and PlayStation 3. The results are encouraging and show that this processor is an interesting option for lattice QCD applications. For a massively parallel machine on the basis of the Cell BE, an application-optimized network needs to be developed.

hep-lat↗
arXiv2007

The nature of the finite temperature QCD transition as a function of the quark masses

The finite temperature QCD transition for physical quark masses is a crossover. For smaller quark masses a first-order phase transition is expected. Using Symanzik improved gauge and stout improved fermion action for 2+1 flavour staggered QCD we give estimates/bounds for the phase line separating the first-order region from the crossover one. The calculations are carried out on two different lattice spacings. Our conclusion for the critical mass is $m_0 \lesssim 0.07 \cdot m_{phys}$ for $N_T=4$ and $m_0 \lesssim 0.12 \cdot m_{phys}$ for $N_T=6$ lattices.

hep-lat↗
arXiv2007

Hadron spectroscopy from canonical partition functions

A spectroscopic method for staggered fermions based on thermodynamical considerations is proposed. The canonical partition functions corresponding to the different quark number sectors are expressed in the low temperature limit as polynomials of the eigenvalues of the reduced fermion matrix. Taking the zero temperature limit yields the masses of the lowest states. The method is successfully applied to the Goldstone pion and both dynamical and quenched results are presented showing good agreement with that of standard spectroscopy. Though in principle the method can be used to obtain the baryon and dibaryon masses, due to their high computational costs such calculations are practically unreachable.

hep-lat↗
arXiv2006

The QCD transition temperature: results with physical masses in the continuum limit

The transition temperature ($T_c$) of QCD is determined by Symanzik improved gauge and stout-link improved staggered fermionic lattice simulations. We use physical masses both for the light quarks ($m_{ud}$) and for the strange quark ($m_s$). Four sets of lattice spacings ($N_t$=4,6,8 and 10) were used to carry out a continuum extrapolation. It turned out that only $N_t$=6,8 and 10 can be used for a controlled extrapolation, $N_t$=4 is out of the scaling region. Since the QCD transition is a non-singular cross-over there is no unique $T_c$. Thus, different observables lead to different numerical $T_c$ values even in the continuum and thermodynamic limit. The peak of the renormalized chiral susceptibility predicts $T_c$=151(3)(3) MeV, wheres $T_c$-s based on the strange quark number susceptibility and Polyakov loops result in 24(4) MeV and 25(4) MeV larger values, respectively. Another consequence of the cross-over is the non-vanishing width of the peaks even in the thermodynamic limit, which we also determine. These numbers are attempted to be the full result for the $T$$\neq$0 transition, though other lattice fermion formulations (e.g. Wilson) are needed to cross-check them.

hep-lat↗
arXiv2006

The order of the quantum chromodynamics transition predicted by the standard model of particle physics

We determine the nature of the QCD transition using lattice calculations for physical quark masses. Susceptibilities are extrapolated to vanishing lattice spacing for three physical volumes, the smallest and largest of which differ by a factor of five. This ensures that a true transition should result in a dramatic increase of the susceptibilities.No such behaviour is observed: our finite-size scaling analysis shows that the finite-temperature QCD transition in the hot early Universe was not a real phase transition, but an analytic crossover (involving a rapid change, as opposed to a jump, as the temperature varied). As such, it will be difficult to find experimental evidence of this transition from astronomical observations.

hep-lat↗
arXiv2006

The equation of state in lattice QCD: with physical quark masses towards the continuum limit

The equation of state of QCD at vanishing chemical potential as a function of temperature is determined for two sets of lattice spacings. Coarser lattices with temporal extension of N_t=4 and finer lattices of N_t=6 are used. Symanzik improved gauge and stout-link improved staggered fermionic actions are applied. The results are given for physical quark masses both for the light quarks and for the strange quark. Pressure, energy density, entropy density, quark number susceptibilities and the speed of sound are presented.

hep-lat↗
arXiv2005

The Density of States Method at Finite Chemical Potential

We study the density of states method to explore the phase diagram of the chiral transition on the temperature and quark chemical potential plane. Four quark flavors are used in the analysis. Though the method is quite expensive small lattices show an indication for a triple-point connecting three different phases on the phase diagram.

hep-lat↗