Y. Maezawa

Strangeness at high temperatures: from hadrons to quarks

Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover, separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window, these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.

The melting and abundance of open charm hadrons

Ratios of cumulants of conserved net charge fluctuations are sensitive to the degrees of freedom that are carriers of the corresponding quantum numbers in different phases of strong interaction matter. Using lattice QCD with 2+1 dynamical flavors and quenched charm quarks we calculate second and fourth order cumulants of net charm fluctuations and their correlations with other conserved charges such as net baryon number, electric charge and strangeness. Analyzing appropriate ratios of these cumulants we probe the nature of charmed degrees of freedom in the vicinity of the QCD chiral crossover region. We show that for temperatures above the chiral crossover transition temperature, charmed degrees of freedom can no longer be described by an uncorrelated gas of hadrons. This suggests that the dissociation of open charm hadrons and the emergence of deconfined charm states sets in just near the chiral crossover transition. Till the crossover region we compare these lattice QCD results with two hadron resonance gas models –including only the experimentally established charmed resonances and also including additional states predicted by quark model and lattice QCD calculations. This comparison provides evidence for so far unobserved charmed hadrons that contribute to the thermodynamics in the crossover region.

Phase structure of finite temperature QCD in the heavy quark region

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 Nf = 1, 2, 3 and 2 + 1 cases. The quark mass dependence of the latent heat is also evaluated in the first order transition region.

Equation of state in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach

We study the equation of state in 2 þ 1 flavor QCD with nonperturbatively improved Wilson quarks coupled with the renormalization group-improved Iwasaki glue. We apply the T-integration method to nonperturbatively calculate the equation of state by the fixed-scale approach. With the fixed-scale approach, we can purely vary the temperature on a line of constant physics without changing the system size and renormalization constants. Unlike the conventional fixed-Nt approach, it is easy to keep scaling violations small at low temperature in the fixed-scale approach. We study 2 þ 1 flavor QCD at light quark mass corresponding to m� =m� ’ 0:63, while the strange quark mass is chosen around the physical point. Although the light quark masses are still heavier than the physical values, our equation of state is roughly consistent with recent results with highly improved staggered quarks at large Nt.

Electric and Magnetic Screening Masses at Finite Temperature from Generalized Polyakov-Line Correlations in Two-flavor Lattice QCD

Screenings of the quark-gluon plasma in electric and magnetic sectors are studied on the basis of generalized Polyakov-line correlation functions in lattice QCD simulations with two flavors of improved Wilson quarks. Using the Euclidean-time reflection (R) and the charge conjugation (C), electric and magnetic screening masses are extracted in a gauge-invariant manner. Long distance behavior of the standard Polyakov-line correlation in the quark-gluon plasma is found to be dictated by the magnetic screening. Also, the ratio of the two screening masses agrees with that obtained from the dimensionally-reduced effective field theory and the N=4 supersymmetric Yang-Mills theory.

In-medium modifications of open and hidden strange-charm mesons from spatial correlation functions

We calculate spatial correlation functions of in-medium mesons consisting of strange-antistrange, strange-anticharm and charm-anticharm quarks in (2 + 1)-flavor lattice QCD using the highly improved staggered quark action. A comparative study of the in-medium modifications of mesons with different flavor contents is performed. We observe significant in-medium modifications for the phi and D-s meson channels already at temperatures around the chiral crossover region. On the other hand, for the J/psi and eta(c) meson channels in-medium modifications remain relatively small around the chiral crossover region and become significant only above 1.3 times the chiral crossover temperature.

Application of Fixed Scale Approach to Static Quark Free Energies in Quenched and 2 + 1 Flavor Lattice QCD with Improved Wilson Quark Action

tions, we adopt the plaquette gauge action on anisotropic 20 3 ×Nt lattices with Nt = 8–26 at the renormalized anisotropy as/at � 4. For 2 + 1 flavor QCD, we adopt the renormalizationgroup improved Iwasaki gluon action and the non-perturbatively O(a)-improved Wilson quark action on isotropic 32 3 × Nt lattices with Nt = 4–12 at mPS/mV =0 .63 (0.74) for the light (strange) flavors. We find that the color-singlet free energies at high temperatures converge to the zero-temperature static-quark potential evaluated from the Wilson-loop at short distances. This is in accordance with the theoretical expectation that the short distance physics is insensitive to the temperature. At long distances, the free energies approach twice the single-quark free energies, implying that the interaction between static quarks is fully screened. We find that the static-quark free energies for various color channels turn out to be well described by the screened Coulomb form, and the color-channel dependence of the inter-quark interaction can be described by the kinetic Casimir factor inspired from the lowest order perturbation theory. We also discuss comparison with a prediction of the thermal perturbation theory and flavor dependence of the screening masses. Subject Index: 231, 234

Meson screening masses at finite temperature with Highly Improved Staggered Quarks

We report on the first study of the screening properties of the mesonicexcitations with strange (

Free energies of heavy quarks in full-QCD lattice simulations with Wilson-type quark action

s

Thermodynamics in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach

) and charm (