arXiv subjects

W. Nörenberg

Publications and source records attributed to W. Nörenberg.

6 recordsLinked to original sources

arXiv2002

Stability and instability of a hot and dilute nuclear droplet. II. Dissipative isoscalar modes

Results on dissipative isoscalar modes of a hot and dilute nuclear droplet are presented. As compared to the adiabatic limit (part I), realistic dissipation yields a substantial reduction of the growth rates for all unstable modes, while the area of spinodal instability in the ($\varrho$,T)-plane remains unchanged. The qualitative features of multifragmentation through spinodal decomposition as obtained in the adiabatic limit are not significantly affected by dissipation.

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arXiv1998

The quark condensate in relativistic nucleus-nucleus collisions

We compute the modification of the quark condensate $<\bar{q} q>$ in relativistic nucleus-nucleus collisions and estimate the 4-volume, where the quark condensate is small ($<\bar{q}q>/<\bar{q} q>_0\leq$ 0.1--0.3) using hadron phase-space distributions obtained with the quark-gluon string model. As a function of the beam energy the 4-volume rises sharply at a beam energy $E_{lab}/A \simeq$ (2--5) GeV, remains roughly constant up to beam energies $\simeq 20$ GeV and rises at higher energies. At low energies the reduction of the condensate is mainly due to baryons, while at higher energies the rise of the 4-volume is due to the abundant mesons produced. Based on our results we expect that moderate beam energies on the order of 10 GeV per nucleon are favourable for studying the restoration of chiral symmetry in a baryon-rich environment in nucleus-nucleus collisions.

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arXiv1998

Thermodynamics of Delta resonances

The thermodynamic potential of a system of pions and nucleons is computed including the piN interactions in the P33 channel. A consistent treatment of the width of the resonance in this channel, the Delta(1232) resonance, is explored in detail. In the low-density limit we recover the leading term of the virial expansion for the thermodynamic potential. An instructive diagrammatic interpretation of the contributions to the total baryon number is presented. Furthermore, we examine within a fireball model the consequences for the pion spectra in heavy-ion collisions at intermediate energies, including the effect of collective flow. A consistent treatment of the Delta width leads to a substantial enhancement of the pion yield at low momenta.

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arXiv1995

Photoproduction of $η$-mesons off protons and deuterons

An effective field theory with hadrons and photons is constructed, where the hadronic parameters are determined by fitting elastic $π$N scattering data. The predicted pion-induced $η$-production on the nucleon agrees well with the data. The hadronic model is then used to describe the final-state interaction in photoinduced processes. We present a consistent description of pion photoproduction in the E$_0^+$-channel and of the total cross sections for photoinduced $η$-production on the proton as well as on the deuteron.

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arXiv1995

The Path of Hot Nuclei Towards Multifragmemtation

The initial production and dynamical expansion of hot spherical nuclei are examined as the first stage in the projectile-multifragmentation process. The initial temperatures, which are necessary for entering the adiabatic spinodal region, as well as the minimum temperatures and densities, which are reached in the expansion, significantly differ for hard and soft equations of state. Additional initial compression, occurring in central collisions leads most likely to a qualitatively different multifragmentation mechanism. Recent experimental data are discussed in relation to the results of the proposed model.

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arXiv1994

Resonance Model for $π$N Scattering and $η$-Meson Production in the s$_{11}$ Channel

A model for $π$N scattering and $η$-meson production in the S$_{11}$ channel is presented. The model includes $π$N-scattering Born terms as well as the N$^*${} resonances S$_{11}$(1535) and S$_{11}$(1610). The $T$-matrix is computed in the $K$-matrix approximation. The parameters of the model are determined by fitting the elastic $π$N-scattering $T$-matrix to empirical data. We find an excellent fit for all energies up to $\sqrt{s}$ = 1.75 GeV. Furthermore, a good description of the cross section for $π^- + p \rightarrow η+ n$ is obtained without further adjustment of parameters.

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