106 research outputs found

    Charmonia above the Deconfinement Phase Transition

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    Analyzing correlation functions of charmonia at finite temperature (TT) on 323×(3296)32^3\times(32-96) anisotropic lattices by the maximum entropy method (MEM), we find that J/ψJ/\psi and ηc\eta_c survive as distinct resonances in the plasma even up to T1.6TcT \simeq 1.6 T_c and that they eventually dissociate between 1.6Tc1.6 T_c and 1.9Tc1.9 T_c (TcT_c is the critical temperature of deconfinement). This suggests that the deconfined plasma is non-perturbative enough to hold heavy-quark bound states. The importance of having sufficient number of temporal data points in the MEM analysis is also emphasized.Comment: Lattice2003(nonzero), 3 pages, 3 figure

    Hadronic Spectral Functions above the QCD Phase Transition

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    We extract the spectral functions in the scalar, pseudo-scalar, vector, and axial vector channels above the deconfinement phase transition temperature (Tc) using the maximum entropy method (MEM). We use anisotropic lattices, 32^3 * 32, 40, 54, 72, 80, and 96 (corresponding to T = 2.3 Tc --> 0.8 Tc), with the renormalized anisotropy xi = 4.0 to have enough temporal data points to carry out the MEM analysis. Our result suggests that the spectral functions continue to possess non-trivial structures even above Tc and in addition that there is a qualitative change in the state of the deconfined matter between 1.5 Tc and 2 Tc.Comment: 3 pages, 4 figures, Lattice2002(nonzerot

    Maximum Entropy Analysis of the Spectral Functions in Lattice QCD

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    First principle calculation of the QCD spectral functions (SPFs) based on the lattice QCD simulations is reviewed. Special emphasis is placed on the Bayesian inference theory and the Maximum Entropy Method (MEM), which is a useful tool to extract SPFs from the imaginary-time correlation functions numerically obtained by the Monte Carlo method. Three important aspects of MEM are (i) it does not require a priori assumptions or parametrizations of SPFs, (ii) for given data, a unique solution is obtained if it exists, and (iii) the statistical significance of the solution can be quantitatively analyzed. The ability of MEM is explicitly demonstrated by using mock data as well as lattice QCD data. When applied to lattice data, MEM correctly reproduces the low-energy resonances and shows the existence of high-energy continuum in hadronic correlation functions. This opens up various possibilities for studying hadronic properties in QCD beyond the conventional way of analyzing the lattice data. Future problems to be studied by MEM in lattice QCD are also summarized.Comment: 51 pages, 17 figures, typos corrected, discussions on the boundary conditions and renormalization constants added. To appear in Progress in Particle and Nuclear Physics, Vol.4

    J/ψJ/\psi and ηc\eta_c in the Deconfined Plasma from Lattice QCD

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    Analyzing correlation functions of charmonia at finite temperature (TT) on 323×(3296)32^3\times(32-96) anisotropic lattices by the maximum entropy method (MEM), we find that J/ψJ/\psi and ηc\eta_c survive as distinct resonances in the plasma even up to T1.6TcT \simeq 1.6 T_c and that they eventually dissociate between 1.6Tc1.6 T_c and 1.9Tc1.9 T_c (TcT_c is the critical temperature of deconfinement). This suggests that the deconfined plasma is non-perturbative enough to hold heavy-quark bound states. The importance of having sufficient number of temporal data points in MEM analyses is also emphasized.Comment: 4 pages, 4 figures, REVTEX, version to appear in Physical Review Letter

    Secondary phi meson peak as an indicator of QCD phase transition in ultrarelativistic heavy ion collisions

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    In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy ion collisions.Comment: 8 pages, 9 uuencoded postscript figures included, Latex, LBL-3572

    Bayesian approach to the first excited nucleon state in lattice QCD

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    We present preliminary results from the first attempt to reconstruct the spectral function in the nucleon and Δ\Delta channels from lattice QCD data using the maximum entropy method (MEM). An advantage of the MEM analysis is to enable us to access information of the excited state spectrum. Performing simulations on two lattice volumes, we confirm the large finite size effect on the first excited nucleon state in the lighter quark mass region.Comment: Lattice2002(spectrum), Latex with espcrc2.sty, 3 pages, 3 figure

    Excited nucleon spectrum from lattice QCD with maximum entropy method

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    We study excited states of the nucleon in quenched lattice QCD with the spectral analysis using the maximum entropy method. Our simulations are performed on three lattice sizes 163×3216^3\times 32, 243×3224^3\times 32 and 323×3232^3\times 32, at β=6.0\beta=6.0 to address the finite volume issue. We find a significant finite volume effect on the mass of the Roper resonance for light quark masses. After removing this systematic error, its mass becomes considerably reduced toward the direction to solve the level order puzzle between the Roper resonance N(1440)N'(1440) and the negative-parity nucleon N(1535)N^*(1535).Comment: Lattice2003(spectrum), 3 pages, 4 figure

    Quasiparticle picture of quarks near chiral transition at finite temperature

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    We investigate, using a chiral effective model, the quark spectrum in the critical region of the chiral transition focusing on the effect of the possible mesonic excitations in the quark-gluon plasma phase. We find that there appears a novel three-peak structure in the quark spectra. We elucidate the mechanism of the appearance of the multi-peak structure with the help of a Yukawa model with an elementary boson.Comment: 4 pages, 5 eps figures, to appear in the proceedings of International Conference on Strong & Electroweak Matter 2006, Brookhaven National Laboratory, USA, May 10-13, 200

    Critical Behavior of J/psi across the Phase Transition from QCD sum rules

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    We study behavior of J/psi in hot gluonic matter using QCD sum rules. Taking into account temperature dependences of the gluon condensates extracted from lattice thermodynamics for the pure SU(3) system, we find that the mass and width of J/psi exhibit rapid change across the critical temperature.Comment: 5 pages, 3 figures. Poster contribution for Quark Matter 2008. To be published in the proceeding
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