Staggered Fermion Thermodynamics using Anisotropic Lattices

Numerical simulations of full QCD on anisotropic lattices provide a convenient way to study QCD thermodynamics with fixed physics scales and reduced lattice spacing errors. We report results from calculations with 2-flavors of dynamical fermions where all bare parameters and hence the physics scales are kept constant while the temperature is changed in small steps by varying only the number of the time slices. The results from a series of zero-temperature scale setting simulations are used to determine the Karsch coefficients and the equation of state at finite temperatures.Comment: Lattice2002(nonzerot), 3 pages, 2 figure

Investigations on the deconfining phase transition in QCD

We investigate the deconfining phase transition in SU(3) pure gauge theory and in full QCD with two flavors of staggered fermions by means of a gauge invariant thermal partition functional. In the pure gauge case our finite size scaling analysis is in agreement with the well known weak first order phase transition. In the case of 2 flavors full QCD we find that the phase transition is consistent with weak first order, contrary to the expectation of a crossover for not too large quark masses.Comment: 3 pages, 3 figures, Lattice2003(topology

Anisotropic Lattices and Dynamical Fermions

We report results from full QCD calculations with two flavors of dynamical staggered fermions on anisotropic lattices. The physical anisotropy as determined from spatial and temporal masses, their corresponding dispersion relations, and spatial and temporal Wilson loops is studied as a function of the bare gauge anisotropy and the bare velocity of light appearing in the Dirac operator. The anisotropy dependence of staggered fermion flavor symmetry breaking is also examined. These results will then be applied to the study of 2-flavor QCD thermodynamics.Comment: Lattice2001(spectrum

A Family of Equations of State Based on Lattice QCD: Impact on Flow in Ultrarelativistic Heavy-Ion Collisions

We construct a family of equations of state within a quasiparticle model by relating pressure, energy density, baryon density and susceptibilities adjusted to first-principles lattice QCD calculations. The relation between pressure and energy density from lattice QCD is surprisingly insensitive to details of the simulations. Effects from different lattice actions, quark masses and lattice spacings used in the simulations show up mostly in the quark-hadron phase transition region which we bridge over by a set of interpolations to a hadron resonance gas equation of state. Within our optimized quasiparticle model we then examine the equation of state along isentropic expansion trajectories at small net baryon densities, as relevant for experiments and hydrodynamic simulations at RHIC and LHC energies. We illustrate its impact on azimuthal flow anisotropies and transverse momentum spectra of various hadron species

Dynamical quark recombination in ultrarelativistic heavy-ion collisions and the proton to pion ratio

We study quark thermal recombination as a function of energy density during the evolution of a heavy-ion collision in a numerical model that reproduces aspects of QCD phenomenology. We show that starting with a set of free quarks (or quarks and antiquarks) the probability to form colorless clusters of three quarks differs from that to form colorless clusters of quark-antiquark and that the former has a sharp jump at a critical energy density whereas the latter transits smoothly from the low to the high energy density domains. We interpret this as a quantitative difference in the production of baryons and mesons with energy density. We use this approach to compute the proton and pion spectra in a Bjorken scenario that incorporates the evolution of these probabilities with energy density, and therefore with proper time. From the spectra, we compute the proton to pion ratio and compare to data at the highest RHIC energies. We show that for a standard choice of parameters, this ratio reaches one, though the maximum is very sensitive to the initial evolution proper time.Comment: 10 pages, 12 figures, version to appear in Phys. Rev.

On the nature and order of the deconfining transition in QCD

The determination of the parameters of the deconfining transition in N_f=2 QCD is discussed, and its relevance to the understanding of the mechanism of color confinement.Comment: 10 pages. In honour of Yu. A. Simonov on his seventyth birthday; to be published in Yadernaya Fizik

Bottomonium Production at RHIC and LHC

Properties of bottomonia (Upsilon, chi_b and Upsilon') in the Quark-Gluon Plasma (QGP) are investigated by assessing inelastic reaction rates and their interplay with open-bottom states (b-quarks or B-mesons) and color-screening. The latter leads to vanishing quarkonium binding energies at sufficiently high temperatures (close to the dissolution point), which, in particular, renders standard gluo-dissociation, g+Upsilon -> b + b-bar, inefficient due to a substantial reduction in final-state phase space. This problem is overcome by invoking a "quasifree" destruction mechanism, g,q,q-bar + Upsilon -> g,q,q-bar + b + b-bar, as previously introduced for charmonia. The pertinent reaction rates are implemented into a kinetic theory framework to evaluate the time evolution of bottomonia in heavy-ion reactions at RHIC and LHC within an expanding fireball model. While bottom quarks are assumed to be exclusively produced in primordial nucleon-nucleon collisions, their thermal relaxation times in the QGP, which importantly figure into Upsilon-formation rates, are estimated according to a recent Fokker-Planck treatment. Predictions for the centrality dependence of Upsilon production are given for upcoming experiments at RHIC and LHC. At both energies, Upsilon suppression turns out to be the prevalent effect.Comment: 16 Pages, 21 figures, 1 table v2: Manuscript reorganized, several sections moved to appendices, additional comments included, contents unchange

Anisotropy beta functions

The flow of couplings under anisotropic scaling of momenta is computed in $\phi^3$ theory in 6 dimensions. It is shown that the coupling decreases as momenta of two of the particles become large, keeping the third momentum fixed, but at a slower rate than the decrease of the coupling if all three momenta become large simultaneously. This effect serves as a simple test of effective theories of high energy scattering, since such theories should reproduce these deviations from the usual logarithmic scale dependence.Comment: uuencoded ps file, 6 page

QCD at non-zero chemical potential and temperature from the lattice

A study of QCD at non-zero chemical potential, mu, and temperature, T, is performed using the lattice technique. The transition temperature (between the confined and deconfined phases) is determined as a function of mu and is found to be in agreement with other work. In addition the variation of the pressure and energy density with mu is obtained for small positive mu. These results are of particular relevance for heavy-ion collision experiments.Comment: Invited paper presented at the Joint Workshop on Physics at the Japanese Hadron Facility, March 2002, Adelaide. 10 pages, uses ws-procs9x6.cls style file (provided