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U. Heinz

Publications and source records attributed to U. Heinz.

81 records · Page 5Linked to original sources
arXiv1997

What can we learn from three-pion interferometry ?

We address the question which additional information on the source shape and dynamics can be extracted from three-particle Bose-Einstein correlations. For chaotic sources the true three-particle correlation term is shown to be sensitive to the momentum dependence of the saddle point of the source and to its asymmetries around that point. For partially coherent sources the three-pion correlator allows to measure the degree of coherence without contamination from resonance decays. We derive the most general Gaussian parametrization of the two- and three-particle correlator for this case and discuss the space-time interpretation of the corresponding parameters.

nucl-th↗
arXiv1997

Three-Point Functions at Finite Temperature

We study 3-point functions at finite temperature in the closed time path formalism. We give a general decomposition of the eight component tensor in terms of seven vertex functions. We derive a spectral representation for these seven functions in terms of two independent real spectral functions. We derive relationships between the seven functions and obtain a representation of the vertex tensor that greatly simplifies calculations in real time.

hep-th↗
arXiv1996

Thermalization and Lyapunov Exponents in the Yang-Mills-Higgs Theory

We investigate thermalization processes occurring at different time scales in the Yang-Mills-Higgs system at high temperatures. We determine the largest Lyapunov exponent associated with the gauge fields and verify its relation to the perturbatively calculated damping rate of a static gauge boson.

hep-th↗
arXiv1996

Kaon Interferometry

Two-kaon and two-pion correlation functions for an expanding thermalized source are compared. In the Yano-Koonin-Podgoretskii parametrization of the correlation function, the HBT radius parameters are shown to obey M_\bot- scaling in the absence of collective transverse flow. This scaling is broken by transverse flow. An accurate comparison of pion and kaon correlations can thus resolve issue whether the observed M_\bot-dependence of the transverse radius parameter is due to transverse collective flow or other transverse gradients. Effects from resonance decays are shortly discussed.

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arXiv1996

Lifetimes and Sizes from Two-Particle Correlation Functions

We discuss the Yano-Koonin-Podgoretskii (YKP) parametrization of the two-particle correlation function for azimuthally symmetric expanding sources. We derive model-independent expressions for the YKP fit parameters and discuss their physical interpretation. We use them to evaluate the YKP fit parameters and their momentum dependence for a simple model for the emission function and propose new strategies for extracting the source lifetime. Longitudinal expansion of the source can be seen directly in the rapidity dependence of the Yano-Koonin velocity.

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arXiv1995

Rapidity Dependence of Strange Particle Ratios in Nuclear Collisions

It was recently found that in sulphur-induced nuclear collisions at 200 A GeV the observed strange hadron abundances can be explained within a thermodynamic model where baryons and mesons separately are in a state of relative chemical equilibrium, with overall strangeness being slightly undersaturated, but distributed among the strange hadron channels according to relative chemical equilibrium with a vanishing strange quark chemical potential. We develop a consistent thermodynamic formulation of the concept of relative chemical equilibrium and show how to introduce into the partition function deviations from absolute chemical equilibrium, e.~g.~an undersaturation of overall strangeness or the breaking of chemical equilibrium between mesons and baryons. We then proceed to test on the available data the hypothesis that the strange quark chemical potential vanishes everywhere, and that the rapidity distributions of all the observed hadrons can be explained in terms of one common, rapidity-dependent function $μ_{\rm q}(η)$ for the baryon chemical potential only. The aim of this study is to shed light on the observed strong rapidity dependence of the strange baryon ratios in the NA36 experiment.

hep-ph↗
arXiv1995

Relativistic Quantum Transport Theory for Electrodynamics

We investigate the relationship between the covariant and the three-dimensional (equal-time) formulations of quantum kinetic theory. We show that the three-dimensional approach can be obtained as the energy average of the covariant formulation. We illustrate this statement in scalar and spinor QED. For scalar QED we derive Lorentz covariant transport and constraint equations directly from the Klein-Gordon equation rather than through the previously used Feshbach-Villars representation. We then consider pair production in a spatially homogeneous but time-dependent electric field and show that the pair density is derived much more easily via the energy averaging method than in the equal-time representation. Proceeding to spinor QED, we derive the covariant version of the equal-time equation derived by Bialynicki-Birula et al. We show that it must be supplemented by another self-adjoint equation to obtain a complete description of the covariant spinor Wigner operator. After spinor decomposition and energy average we study the classical limit of the resulting three-dimensional kinetic equations. There are only two independent spinor components in this limit, the mass density and the spin density, and we derive also their covariant equations of motion. We then show that the equal-time kinetic equation provides a complete description only for constant external electromagnetic fields, but is in general incomplete. It must be supplemented by additional constraints which we derive explicitly from the covariant formulation.

nucl-th↗
arXiv1992

Strangeness Conservation in Hot Nuclear Fireballs

A constraint between thermal fireball parameters arises from the requirement that the balance of strangeness in a fireball is (nearly) zero. We study the impact of this constraint on (multi-)strange (anti-)baryon multiplicities and compare the hadron gas and quark-gluon plasma predictions. We explore the relation between the entropy content and particle multiplicities and show that the data are compatible with the quark-gluon plasma hypothesis, but appear to be inconsistent with the picture of an equilibrated hadron gas fireball. We consider the implications of the results on the dynamics of evolution and decay of the particle source.

hep-ph↗