arXiv subjects

O. Kaczmarek

Publications and source records attributed to O. Kaczmarek.

At least 73 records · Page 4Linked to original sources

arXiv2005

The screening length in hot QCD

We discuss the temperature dependence of the screening lengths in quenched and full QCD using the non-perturbative lattice approach. We analyze the temperature dependence of distances which are defined as moments of quark antiquark free energies. These distance scales are supposed to describe the geometric size of partonic clouds which screen static charges in a medium and characterize distances beyond which the quark antiquark free energy is to large extent dominated by medium effects. At asymptotic high temperatures these moments can be related to the inverse Debye mass. In our numeric analysis we find that these moments drop rapidly in the vicinity of the phase transition and indicate distances which are about twice as large as the inverse Debye mass found in earlier studies. Our analysis supports recent findings that indicate that $J/ψ$ will show significant medium modifications only at temperatures well above $T_c$.

hep-lat↗

arXiv2005

Static quark anti-quark free and internal energy in 2-flavor QCD and bound states in the QGP

We present results on heavy quark free energies in 2-flavour QCD. The temperature dependence of the interaction between static quark anti-quark pairs will be analyzed in terms of temperature dependent screening radii, which give a first estimate on the medium modification of (heavy quark) bound states in the quark gluon plasma. Comparing those radii to the (zero temperature) mean squared charge radii of cha rmonium states indicates that the $J/ψ$ may survive the phase transition as a bound state, while $χ_c$ and $ψ'$ are expected to show significant thermal modifications at temperatures close to the transition. Furthermore we will analyze the relation between heavy quark free energies, entropy contributions and internal energy and discuss their relation to potential models used to analyze the melting of heavy quark bound states above the deconfinement temperature. Results of different groups and various potential models for bound states in the deconfined phase of QCD are compared.

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arXiv2005

The QCD equation of state for two flavours at non-zero chemical potential

We present results of a simulation of 2 flavour QCD on a $16^3\times4$ lattice using p4-improved staggered fermions with bare quark mass $m/T=0.4$. Derivatives of the thermodynamic grand canonical partition function $Z(V,T,μ_u,μ_d)$ with respect to chemical potentials $μ_{u,d}$ for different quark flavours are calculated up to sixth order, enabling estimates of the pressure and the quark number density as well as the chiral condensate and various susceptibilities as functions of $μ_{u,d}$ via Taylor series expansion. Results are compared to high temperature perturbation theory as well as a hadron resonance gas model. We also analyze baryon as well as isospin fluctuations and discuss the relation to the chiral critical point in the QCD phase diagram. We moreover discuss the dependence of the heavy quark free energy on the chemical potential.

hep-ph↗

arXiv2005

Heavy quark free energies and screening at finite temperature and density

We study the free energies of heavy quarks calculated from Polyakov loop correlation functions in full 2-flavour QCD using the p4-improved staggered fermion action. A small but finite Baryon number density is included via Taylor expansion of the fermion determinant in the Baryo-chemical potential mu. For temperatures above Tc we extract Debye screening masses from the large distance behaviour of the free energies and compare their mu-dependence to perturbative results.

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arXiv2005

Heavy two- and three-quark free energies at finite $T$

We investigate the behaviour of heavy $QQ$- and $QQQ$-free energies in SU(3) pure gauge theory at finite temperature. After stating some general properties of the free energies, we discuss the $QQ$-antitriplet and -sextet channels as well as free energies in different $QQQ$-channels. We perform a detailed finite volume scaling analysis of $QQ$-free energies below and above $T_c$. Moreover, we also discuss the relation of the $QQ$-antitriplet to the $Q\bar Q$-singlet free energies. A comparison of the effective running coupling indicates that the $r$-dependence of the free energies differs by a factor of two in agreement with the different Casimir factors. We observe that the baryonic free energies can be decomposed into a sum of two particle interactions.

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arXiv2005

Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential

We analyze the dependence of heavy quark free energies on the baryon chemical potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the chemical potential which circumvents the sign problem. The Taylor expansion coefficients of colour singlet and colour averaged free energies are calculated and from this the expansion coefficients for the corresponding screening masses are determined. We find that for small mu_b the free energies of a static quark anti-quark pair decrease in a medium with a net excess of quarks and that screening is well described by a screening mass which increases with increasing mu_b. The mu_b-dependent corrections to the screening masses are well described by perturbation theory for T > 2 T_c. In particular, we find for all temperatures above T_c that the expansion coefficients for singlet and colour averaged screening masses differ by a factor 2.

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arXiv2005

Heavy Quarkonium Physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

hep-ph↗

arXiv2005

Static quark anti-quark interactions at zero and finite temperature QCD. II.Quark anti-quark internal energy and entropy

We analyze the change in free energy, internal energy and entropy due to the presence of a heavy quark anti-quark pair in a QCD heat bath. The internal energies and entropies are introduced as intensive observables calculated through thermal derivatives of the QCD partition function containing additional static color sources. The quark anti-quark internal energy and, in particular, the entropy clearly signal the phase change from quark confinement below and deconfinement above the transition and both observables are introduced such that they survive the continuum limit. The intermediate and large distance behavior of the energies reflect string breaking and color screening phenomena. This is used to characterize the energies which are needed to dissolve heavy quarkonium states in a thermal medium. Our discussion supports recent findings which suggest that parts of the quarkonium systems may survive the phase transition and dissolve only at higher temperatures.

hep-lat↗

arXiv2005

Heavy Quark Interactions in Finite Temperature QCD

We study the free energy of a heavy quark-antiquark pair in a thermal medium. We constuct a simple ansatz for the free energy for two quark flavors motivated by the Debye-Hückel theory of screening.

hep-ph↗

arXiv2005

Heavy quark potential and quarkonia dissociation rates

Quenched lattice data for the quark-antiquark interaction (in terms of heavy quark free energies) in the color singlet channel at finite temperatures are fitted and used within the nonrelativistic Schroedinger equation formalism to obtain binding energies and scattering phase shifts for the lowest eigenstates in the charmonium and bottomonium systems in a hot gluon plasma. The partial dissociation rate due to the Bhanot-Peskin process is calculated using different assumptions for the gluon distribution function, including free massless gluons, massive gluons, and massive damped gluons. It is demonstrated that a temperature dependent gluon mass has an essential influence on the heavy quarkonia dissociation, but that this process alone is insufficient to describe the heavy quarkonia dissociation rates.

hep-ph↗

arXiv2005

QCD at non-zero temperature and density from the lattice

The study of systems as diverse as the cores of neutron stars and heavy-ion collision experiments requires the understanding of the phase structure of QCD at non-zero temperature, T, and chemical potential, mu_q. We review some of the difficulties of performing lattice simulations of QCD with non-zero mu_q, and outline the re-weighting method used to overcome this problem. This method is used to determine the critical endpoint of QCD in the (mu_q,T) plane. We study the pressure and quark number susceptibility at small mu_q.

hep-lat↗

arXiv2005

Thermodynamics of Two Flavor QCD to Sixth Order in Quark Chemical Potential

We present results of a simulation of 2-flavor QCD on a 4x16^3 lattice using p4-improved staggered fermions with bare quark mass m/T=0.4. Derivatives of the thermodynamic grand canonical partition function Z(V,T,mu_u,mu_d) with respect to chemical potentials mu_(u,d) for different quark flavors are calculated up to sixth order, enabling estimates of the pressure and the quark number density as well as the chiral condensate and various susceptibilities as functions of mu_q = (mu_u + mu_d)/2 via Taylor series expansion. Furthermore, we analyze baryon as well as isospin fluctuations and discuss the relation between the radius of convergence of the Taylor series and the chiral critical point in the QCD phase diagram. We argue that bulk thermodynamic observables do not, at present, provide direct evidence for the existence of a chiral critical point in the QCD phase diagram. Results are compared to high temperature perturbation theory as well as a hadron resonance gas model.

hep-lat↗

arXiv2004

Fluctuations in the vicinity of the phase transition line for two flavor QCD

We study the susceptibilities of quark number, isospin number and electric charge in numerical simulations of lattice QCD at high temperature and density. We discuss the equation of state for 2 flavor QCD at non-zero temperature and density. Derivatives of $\ln Z$ with respect to quark chemical potential $(μ_q)$ are calculated up to sixth order. From this Taylor series, the susceptibilities are estimated as functions of temperature and $μ_q$. Moreover, we comment on the hadron resonance gas model, which explains well our simulation results below $T_c$.

hep-lat↗

arXiv2004

Numerical study of the equation of state for two flavor QCD at non-zero baryon density

We discuss the equation of state (EoS) for two flavor QCD at non-zero temperature and density. Derivatives of $\ln Z$ with respect to quark chemical potential $μ_q$ are calculated up to sixth order. From this Taylor series, the pressure, quark number density and associated susceptibilities are estimated as functions of temperature and $μ_q$. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as $μ_q$ is increased. This suggests the presence of a critical endpoint in the $(μ_q, T)$ plane. Moreover, we comment on the hadron resonance gas model, which explains well our simulation results below $T_c$.

hep-lat↗

arXiv2004

Free energies of static three quark systems

We study the behaviour of free energies of baryonic systems composed of three heavy quarks on the lattice in SU(3) pure gauge theory at finite temperature. For all temperatures above $T_c$ we find that the connected part of the singlet (decuplet) free energy of the three quark system is given by the sum of the connected parts of the free energies of $qq$-triplets (-sextets). Using renormalized free energies we can compare free energies in different colour channels as well as those of $qq$- and $qqq$-systems on an unique energy scale.

hep-lat↗

arXiv2004

Static quark anti-quark free energy and the running coupling at finite temperature

We analyze the free energy of a static quark anti-quark pair in quenched QCD at short and large distances. From this we deduce running couplings, g^2(r,T), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance non-perturbative regime in the QCD plasma phase. Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. Our analysis suggests that it is more appropriate to characterize the non-perturbative properties of the QCD plasma phase close to T_c in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force.

hep-lat↗

arXiv2003

Numerical study of the equation of state for two flavor QCD at finite density

We discuss the equation of state for 2 flavor QCD at non-zero temperature and density. Derivatives of $\ln Z$ with respect to quark chemical potential $μ_q$ up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of $μ_q$ via a Taylor series expansion. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as $μ_q$ is increased. This suggests the presence of a critical endpoint in the $(T, μ_q)$ plane.

hep-lat↗

arXiv2003

Heavy quark free energies, potentials and the renormalized Polyakov loop

We discuss the renormalized free energy of a heavy quark anti-quark pair in the color singlet channel for quenched and full QCD at finite temperature. The temperature and mass dependence, as well as its short distance behavior is analyzed. Using the free energies we calculate the heavy quark potential and entropy in quenched QCD. The asymptotic large distance behavior of the free energy is used to define the non-perturbatively renormalized Polyakov loop which is well behaved in the continuum limit. String breaking is studied in the color singlet channel in 2-flavor QCD.

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