18764006
Nonequilibrium dynamics of a hadronizing quark-gluon plasma
We investigate the hadronic cooling of a quark droplet within a microscopic model. The color flux tube approach is used to describe the hadronization of the quark phase. The model reproduces experimental particle ratios equally well compared to a static thermal hadronic source. Furthermore, the dynamics of the decomposition of a quark-gluon plasma is investigated and time dependent particle ratios are found.
126346677
Collective Flow Signals the Quark-Gluon Plasma
A critical discussion of the present status of the CERN experiments on hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A·GeV: here the hydrodynamic model has predicted the collapse of the ]]> v_1$ flow and of the v2 flow at ∼10 A·GeV; at 40 A·GeV it has been recently observed by the NA49 Collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as potential evidence for a first order phase transition at high baryon density ρB. A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Here, hadronic rescattering models can explain 2 GeV/c. This is interpreted as evidence for the production of superdense matter at RHIC with initial pressure far above hadronic pressure, p > 1 GeV/fm3. We suggest that the fluctuations in the flow, v1 and v2, should be measured in future since ideal hydrodynamics predicts that they are larger than 50% due to initial state fluctuations. Furthermore, the QGP coefficient of viscosity may be determined experimentally from the fluctuations observed.
119364125
Exotic hadrons from dynamical clustering of quarks in ultrarelativistic heavy ion collisions
Results from a model study on the formation of exotic quark clusters at the hadronization stage of a heavy ion collision are presented. The dynamical quark molecular dynamics (qMD) model which is used is sketched, and results for exotica made of up to six (anti-)quarks are shown. The second part focuses on pentaquarks. The rapidity distribution are shown, and the distribution of strangeness is found to yield an indicator of thermalization and homogenization of the deconfined quark system. Relative Θ+ yields are found to be lower than thermal model estimates.
201855044
Parton Recombination And Fluctuations Of Conserved Charges
We study various fluctuation and correlation signals of the d econfined state using a dynamical recombination approach (quark Molecular Dynamics, qMD). We a nalyse charge ratio fluctuations, charge transfer fluctuations and baryon-strangeness corre lations as a function of the center of mass energy with a set of central Pb+Pb/Au+Au events from AGS energies on ( Elab = 4 AGeV) up to the highest RHIC energy available ( √ sNN = 200 GeV) and as a function of time with a set of central Au+Au qMD events at √ sNN = 200 GeV with and without applying our hadronization procedure. For all studied quantities, the results start fr om values compatible with a weakly coupled QGP in the early stage and end with values compatible wit h the hadronic result in the final state. We show that the loss of the signal occurs at the same ti me as hadronization and trace it back to the dynamical recombination process implemented in our model.
125800824
Critical review of quark gluon plasma signatures
We discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions, using insight gained from non‐equilibrium models (three‐fluid hydrodynamics and the hadronic transport model UrQMD). It is demonstrated that these two models ‐ although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) ‐ both yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Ψ meson production/suppression, strange matter formation, dileptons, and directed flow (bounce‐off and squeeze‐out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data.
278178
Physics opportunities at RHIC and LHC
Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models—although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles)—all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Ψ meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from dat...
122955732
Chiral Perturbation Theory for Baryons
So far we have considered the purely mesonic sector of chiral perturbation theory, involving the interaction of Goldstone bosons with each other and with external fields. However, ChPT can be extended to also describe the dynamics of baryons at low energies. Here we will concentrate on matrix elements with a single baryon in the initial and final states. As in the mesonic sector, Green functions are calculated in an effective-Lagrangian approach in combination with a power counting. The symmetries of QCD and the pattern of their breaking again constrain the possible interaction terms appearing in the effective Lagrangian, and we will discuss several approaches to obtain a consistent power counting.
117594500
Spontaneous Symmetry Breaking and the Goldstone Theorem
So far we have concentrated on the chiral symmetry of the QCD Hamiltonian and the explicit symmetry breaking by the quark masses. We have discussed the importance of chiral symmetry for the properties of Green functions with particular emphasis on the relations among different Green functions as expressed through the chiral Ward identities. Now it is time to address a second aspect which, for the low-energy structure of QCD, is equally important, namely, the concept of spontaneous symmetry breaking. A (continuous) symmetry is said to be spontaneously broken or hidden if the ground state of the system is no longer invariant under the full symmetry group of the Hamiltonian. In this chapter we will first illustrate this by means of a discrete symmetry and then turn to the case of a spontaneously broken continuous global symmetry.
15477090
Recent developments in effective field theory
Abstract We will give a short introduction to the one-nucleon sector of chiral perturbation theory and will address the issue of a consistent power counting and renormalization. We will discuss the infrared regularization and the extended on-mass-shell scheme. Both allow for the inclusion of further degrees of freedom beyond pions and nucleons and the application to higher-loop calculations. As applications we consider the chiral expansion of the nucleon mass to order O ( q 6 ) and the inclusion of vector and axial-vector mesons in the calculation of nucleon form factors.
15270133
BARYON CHIRAL PERTURBATION THEORY IN MANIFESTLY LORENTZ-INVARIANT FORM
A successful effective field theory program requires besides the most general effective Lagrangian a perturbative expansion scheme for observables in terms of a consistent power counting method. We discuss a renormalization scheme for manifestly Lorentz-invariant baryon chiral perturbation theory generating a simple and consistent power counting for renormalized diagrams. The approach may be used in an iterative procedure to renormalize higher-order loop diagrams and also allows for implementing a consistent power counting when vector mesons are explicitly included.
13532458
Pion polarizabilities: No conflict between dispersion theory and ChPT
Recent attempts to determine the pion polarizability by dispersion relations yield values that disagree with the predictions of chiral perturbation theory. These dispersion relations are based on specific forms for the absorptive part of the Compton amplitudes. The analytic properties of these forms are examined, and the strong enhancement of intermediate-meson contributions is shown to be connected to non-analytic structures