Consequences of covariant kaon dynamics in heavy ion collisions

The influence of the chiral mean field on the kaon dynamics in heavy ion reactions is investigated. Inside the nuclear medium the kaons are described as dressed quasi-particles carrying effective masses and momenta. A momentum dependent part of the interaction which resembles a Lorentz force originates from spatial components of the vector field and provides an important contribution to the in-medium kaon dynamics. This contribution is found to counterbalance the influence of the vector potential on the $K^+$ in-plane flow to a strong extent. Thus it appears to be difficult to restrict the in-medium potential from the analysis of the corresponding transverse flow.Comment: 14 pages, RevTex, 3 PS figures, accepted for publication in Phys. Lett.

Radial flow of kaon mesons in heavy ion reactions

This work investigates the collective motion of kaons in heavy ion reactions at SIS energies (about 1-2 GeV/nucleon). A radial collective flow of $K^+$ mesons is predicted to exist in central Au + Au collisions, which manifests in a characteristic "shoulder-arm" shape of the transverse mass spectrum of the midrapidity $K^+$ mesons. The $K^+$ radial flow arises from the repulsive $K^+$ mean field in nuclear matter. In spite of a strong reabsorption and rescattering the attractive $K^-$ mean field leads as well to a collective radial flow of $K^-$ mesons. The $K^-$ radial flow, however, is different from that of $K^+$ mesons and can be observed by a characteristic "concave" structure of the transverse mass spectrum of the $K^-$ mesons emitted at midrapidity. The kaon radial flows can therefore serve as a novel tool for the investigation of kaon properties in dense nuclear matter.Comment: 30 pages RevTex, 5 PS figures, accepted for publication in Phys. Rev.

J/ψJ/\psi normal and anomalous suppressions in a hadron and string cascade model

A mechanism for the effective dissociation of a $c\bar{c}$ pair in the colour electric field of strings is introduced into a hadron and string cascade model, i.e. JPCIAE, which is based on the LUND model, simulating ultra-relativistic nucleus - nucleus collisions. This new mechanism together with the known mechanism of nuclear absorption (both baryons and mesons) could reproduce fairly the data of the normal and anomalous $J/\psi$ suppressions in minimum bias pA, AB (with light projectile), and Pb + Pb collisions at 200 A GeV/c. However the impact parameter (E_T) dependence of the $J/\psi$ suppression factor, both, in S + U and Pb + Pb reactions at 200 A GeV/c and 158 A GeV/c, respectively, is not well reproduced. We also tested the additional mechanism of the energy degradation of leading particles, with which both, the normal and anomalous $J/\psi$ suppressions in minimum bias pA, AB, and Pb + Pb collisions and the E_T dependence of the $J/\psi$ suppression factor are better reproduced.Comment: 16 pages (RevTex), 6 ps-figures, to be published in J. Phys.

Stability of the B=2 hedgehog in the Skyrme model

We study the unstable modes of the baryon number two hedgehog of the Skyrme model on a three dimensional spatial lattice. An expansion of the Skyrme Lagrangian around the hedgehog configuration provides the equations of motion for the fluctuation fields solvable numerically via a relaxation method. We find the negative energy modes and, by evolving the excited hedgehog in time, a breakup into two separated solitonic configurations is obtained. Different paths of descent for the receding Skyrmions are presented and the possibility of determining the metric structure of the collective-coordinate manifold is discussed.Comment: 22 pages Latex, 9 uuencoded figures include

The deformation of the interacting nucleon in the Skyrme model

Changes in the nucleon shape are investigated by letting the nucleon deform under the strong interactions with another nucleon. The parameters of the axial deformations are obtained by minimizing the static energy of the two nucleon system at each internucleon distance $R$. It is shown that the intrinsic quadrupole moment of the interacting proton, $Q_{p}$, is about $0.02 fm^2$ at distances near $R \sim 1.25$ fm.Comment: 11 pages, uudecode, gzip, tar, latex, 3 eps figures, accepted for the publication by Phys.Lett.

Scalar and vector decomposition of the nucleon self-energy in the relativistic Brueckner approach

We investigate the momentum dependence of the nucleon self-energy in nuclear matter. We apply the relativistic Brueckner-Hartree-Fock approach and adopt the Bonn A potential. A strong momentum dependence of the scalar and vector self-energy components can be observed when a commonly used pseudo-vector choice for the covariant representation of the T-matrix is applied. This momentum dependence is dominated by the pion exchange. We discuss the problems of this choice and its relations to on-shell ambiguities of the T-matrix representation. Starting from a complete pseudo-vector representation of the T-matrix, which reproduces correctly the pseudo-vector pion-exchange contributions at the Hartree-Fock level, we observe a much weaker momentum dependence of the self-energy. This fixes the range of the inherent uncertainty in the determination of the scalar and vector self-energy components. Comparing to other work, we find that extracting the self-energy components by a fit to the single particle potential leads to even more ambiguous results.Comment: 35 pages RevTex, 7 PS figures, replaced by a revised and extended versio

Scalar Mesons in a Chiral Quark Model with Glueball

Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3)xU(3) chiral quark model of the Nambu--Jona-Lasinio (NJL) type with 't Hooft interaction. The latter interaction produces singlet-octet mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and the glueball and their main modes of strong decay are described.Comment: 10 pages, LaTeX text, requires svjour.cls and svepj.cl

Skyrmiondynamik und die Nukleon-Nukleon-Wechselwirkung

Within the Skyrme model we study the low energy inter action of nucleons in the baryon number B=2 sector. Starting with the non-perturbative interaction of individualB=1 skyrmions we construct a B=2 hamiltonian which is used for the description of the nucleon-nucleon interaction. Using this hamiltonian we obtain semi-quantitative results for the nucleon-nucleon potential and for the properties of the deuteron. Having its origin in the large-Nc expansion of QCD, the Skyrme model is viewed as aneffective model of the strong interaction. This connection is presented in the first part of the work where also a semi-classical treatment of the nucleons via the solitonic description is applied. Some results for the B=1 sector are presented which confirm that the Skyrme model can serve as a very interesting model in the field of low energy hadronic physics. In the second part of this work we investigate the nonlinear interaction of two B=1 skyrmions. Using advanced numerical grid-methods we are able to calculate the relevant configurations in the B=2 sector. Of importance is the method of steepest descent developed in this work. Applying this special method to our problem we obtain different solitonic configurations which are of importance for a first description of the nucleon-nucleon interaction. Via the collective coordinate method we are able to describe approximately the dynamics of skyrmions and to deduce a collective coordinate hamiltonian. This model hamiltonian is used furt her in the third part of the work where we study the inter action of nucleons. We use the Born-Oppenheimer approximation in order to calulate the nucleon-nucleon potential and to obtain results for the properties of the bound state of two nucleons, the deuteron. The binding energy of the deuteron is calculated in different approximation schemes and certain properties of the deuteron, like the mean charge radius and the quadrupol moment are investigated in detail. The result we obtain are in satisfactory agreement to the experimentally known values. This shows that the Skyrme model can be viewed in the B=2 sector as weIl as an effective model of thestrong interaction

Skyrmiondynamik und die Nukleon-Nukleon-Wechselwirkung

Within the Skyrme model we study the low energy interaction of nucleons in the baryon number B=2 sector. Starting with the non-perturbative interaction of individual B=1 skyrmions we construct a B=2 Hamiltonian which is used for the description of the nucleon-nucleon interaction. Using this Hamiltonian we obtain semi-quantitative results for the nucleon-nucleon potential and for the properties of the deuteron. Having its origin in the large-N_c expansion of QCD, the Skyrme model is viewed as an effective model of the strong interaction. This connection is presented in the first part of the work where also a semi-classical treatment of the nucleons via the solitonic description is applied. Some results for the B=1 sector are presented which confirm that the Skyrme model can serve as a very interesting model in the field of low energy hadronic physics. In the second part of this work we investigate the nonlinear interaction of two B=1 skyrmions. Using advanced numerical grid-methods we are able to calculate the relevant configurations in the B=2 sector. Of importance is the method of steepest descent developed in this work. Applying this special method to our problem we obtain different solitonic configurations which are of importance for a first description of the nucleon-nucleon interaction. Via the collective coordinate method we are able to describe approximately the dynamics of skyrmions and to deduce a collective coordinate Hamiltonian. This model Hamiltonian is used further in the third part of the work where we study the interaction of nucleons. We use the Born-Oppenheimer approximation in order to calulate the nucleon-nucleon potentialSIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman