arXiv subjects
Publications and source records attributed to Volker Koch.
These lectures are an attempt to a pedagogical introduction into the elementary concepts of chiral symmetry in nuclear physics. Effective chiral models such as the linear and nonlinear sigma model will be discussed as well as the essential ideas of chiral perturbation theory. Some applications to the physics of ultrarelativistic heavy ion collisions will be presented.
We study finite temperature effects on dilepton production from pion-pion annihilation in hot hadronic matter. The softening of the pion dispersion relation in a medium is found to enhance the production rate of dileptons with invariant masses in the region of $2m^*_π(T)<M<m_ρ$. On the other hand, the reduction of the pion electromagnetic form factor at finite temperature leads to a suppression of the dilepton production rate. Including both effects, we have found that the dilepton yield is slightly enhanced in the invariant mass region $M= 270\sim 600$ MeV but is suppressed around the vector meson resonance. We further discuss the relevance of our results to recent experimental data from the S+Au collisions at CERN/SPS energies by the CERES collaboration.
The E814-collaboration has found a component of very low $m_t$ $K^+$ mesons with a slope parameter of $T \sim 15 \, \rm MeV$. We will present a scenario which explains the observed slope parameter and which allows us to predict the expected slope parameter for kaons produced in heavier systems such as Au+Au. We also will discuss the effect of the coulomb interaction on the structure of the spectrum.
The scattering of antikaons with nucleons is studied in the nuclear environment. Describing the $\lam$ as a $K^-$ proton bound state, we find, that due to the Pauli blocking of intermediate states, the mass of the $Λ(1405)$ is shifted upwards in energy, above the $K^-$ proton threshold and and its width is somewhat broadened. As a consequence the s-wave $K^-$--nucleon scattering length turns attractive at finite nucleon density ($ρ\geq 0.25 ρ_0$) leading to a mean field potential for the $K^-$ of about $\sim -100 \, \rm MeV$ in nuclear matter at ground state density. Consequences for Heavy Ion collisions and possible experimental checks for the structure of the $\lam$ are discussed. (Figures will be sent on request)
The E814-collaboration has found a component of very low $m_t$ $K^+$ mesons with a slope parameter of $T \sim 15 \, \rm MeV$. We will present a scenario which explains the observed slope parameter and which allows us to predict the expected slope parameter for kaons produced in heavier systems such as Au+Au. Implications for the restoration of chiral symmetry in relativistic heavy ion collisions are discussed.(figures are being sent on request)
We study the temperature dependence of quark antiquark correlations in the space like direction. In particular, we predict the temperature dependence of space like Bethe-Salpeter amplitudes using recent Lattice gauge data for the space like string potential. We also investigate the effect of the space like string potential on the screening mass and discuss possible corrections which may arise when working with point sources.
The effect of collective potentials on pion spectra in ultrarelativistic heavy ion collisions is investigated. We find the effect of these potential to be very small, too small to explain the observed enhancement at low transverse momenta. (7 figures, bill be send on request)