arXiv subjects

Klaus Geiger

Publications and source records attributed to Klaus Geiger.

23 records · Page 2Linked to original sources

arXiv1995

Quantum Field Kinetics of QCD: Quark-Gluon Transport Theory for Lightcone Dominated Processes

A quantum kinetic formalism is developed to study the dynamical interplay of quantum and statistical-kinetic properties of non-equilibrium multi-parton systems produced in high-energy QCD processes. The approach provides the means to follow the quantum dynamics in both space-time and energy-momentum, starting from an arbitrary initial configuration of high-momentum quarks and gluons. Using a generalized functional integral representation and adopting the `closed-time-path' Green function techniques, a self-consistent set of equations of motions is obtained: a Ginzburg-Landau equation for a possible color background field, and Dyson-Schwinger equations for the 2-point functions of the gluon and quark fields. By exploiting the `two-scale nature' of light-cone dominated QCD processes, i.e. the separation between the quantum scale that specifies the range of short-distance quantum fluctuations, and the kinetic scale that characterizes the range of statistical binary inter- actions, the quantum-field equations of motion are converted into a correspon- ding set of `renormalization equations' and `transport equations'. The former describe renormalization and dissipation effects through the evolution of the spectral density of individual, dressed partons, whereas the latter determine the statistical occurrence of scattering processes among these dressed partons. The renormalization equations and the transport equations are coupled, and hence must be solved self-consistently. This amounts to evolving the multi-parton system, from a specified initial configuration, in time and full 7-dimensional phase-space. This description provides a proba- bilistic interpretation and is therefore of important practical value for the solution of the dynamical equations of motion, e.g. by Monte Carlo simulation.

hep-ph↗

arXiv1995

REAL-TIME DESCRIPTION OF PARTON-HADRON CONVERSION AND CONFINEMENT DYNAMICS

We propose a new and universal approach to the hadronization problem that incorporates both partonic and hadronic degrees of freedom in their respective domains of relevance, and that describes the conversion between them within a kinetic field theory formulation in real time and full 7-dimensional phase space. We construct a scale-dependent effective theory that reduces to perturbative QCD with its scale and chiral symmetry properties at short space-time distances, but at large distances (r > 1 fm) yields symmetry breaking gluon and quark condensates plus hadronic excitations. The approach is applied to the evolution of fragmenting qq~ and gg jet pairs as the system evolves from the initial 2-jet configuration, via parton showering and cluster formation, to the final yield of hadrons. The phenomenological implications for e+e- -> hadrons are investigated, such as the time scale of the transition, and its energy dependence, cluster size and mass distributions. We compare our results for particle production and Bose-Einstein correlations with experimental data, and find an interesting possibility of extracting the basic parameters of the space-time evolution of the system from Bose enhancement measurements.

hep-ph↗

arXiv1995

REAL-TIME DYNAMICS OF PARTON-HADRON CONVERSION

We propose a new and universal approach to the hadronization problem that incorporates both perturbative QCD and effective field theory in their respective domains of validity and that models the transition between them in analogy to the finite temperature QCD phase transition. Using techniques of quantum kinetic theory, we formulate a real-time description in momentum and position space. The approach is applied to the evolution of fragmenting $q\bar q$ and $gg$ jets as the system evolves from the initial 2-jet, via parton multiplication and cluster formation, to the final yield of hadrons. We investigate time scale of the transition, energy dependence, cluster size and mass distributions, and compare our results for particle production and Bose-Einstein correlations with experimental data for $e^+e^-\rightarrow hadrons$. An interesting possibility to extract the space-time evolution of the system from Bose enhancement measurements is suggested.

hep-ph↗

arXiv1994

High Density QCD and Entropy Production at Heavy Ion Colliders

The role of entropy production in the context of probing QCD properties at high densities and finite temperatures in ultra-relativistic collisions of heavy nuclei is inspected. It is argued that the entropy generated in these reactions provides a powerful tool to investigate the space-time evolution and the question whether and how a deconfined plasma of quarks and gluons is formed. I will address the questions how entropy is produced, and how it is measurable. The uncertainties in predicting the different contributions to the total entropy and particle multiplicities during the course of heavy ion collisions are also discussed.

hep-ph↗

arXiv1993

QCD Evolution Equations for High Energy Partons in Nuclear Matter

We derive a generalized form of Altarelli-Parisi equations to decribe the time evolution of parton distributions in a nuclear medium. In the framework of the leading logarithmic approximation, we obtain a set of coupled integro- differential equations for the parton distribution functions and equations for the virtuality (``age'') distribution of partons. In addition to parton branching processes, we take into account fusion and scattering processes that are specific to QCD in medium. Detailed balance between gain and loss terms in the resulting evolution equations correctly accounts for both real and virtual contributions which yields a natural cancellation of infrared divergences.

hep-ph↗