arXiv subjects
Publications and source records attributed to B. Kampfer.
Within a transport code of BUU type the production of phi-mesons in the reactions Ni+Ni at 1.93 AGeV and Ru+Ru at 1.69 AGeV is studied. New elementary reaction channels rho+N(Delta) to phi+N and pi+N(1520) to phi+N are included. In spite of a substantial increase of the ϕmultiplicities by these channels the results stay below the tentative numbers extracted from experimental data.
The preliminary experimental data on $ϕ$ production in the reaction Ni(1.93 AGeV) + Ni point to a puzzling high $ϕ$ yield which can not be reproduced with present transport codes. We survey the experimental situation and present prospects for dedicated measurements of the $ϕ$ multiplicities with the $K^+ K^-$ and $e^+ e^-$ channels at HADES and FOPI.
The centrality dependence of thermal parameters, characterizing the hadron multiplicities, is determined phenomenologically for lead-on-lead collisions at CERN-SPS for a beam energy of 158 AGeV. The strangeness equilibration factor shows a clear, approximately linear, increase with increasing centrality, while the freeze-out temperature and chemical potential remain constant.
The isoscalar-isovector ($ρ-ω$) interferences in the exclusive reactions $π^- p \to n e^+ e^-$ and $π^+ n \to p e^+ e^-$ near the $ω$ threshold leads to a distinct difference of the dielectron invariant mass distributions depending on beam energy. The strength of this effect is determined by the coupling of resonances to the nucleon vector-meson channels and other resonance properties. Therefore, a combined analysis of these reactions can be used as a tool for determining the baryon resonance dynamics.
Recent finite-temperature QCD lattice data are analyzed within a quasiparticle model, and extrapolated to nonzero chemical potential. Determined by the chiral transition temperature, the resulting equation of state of charge neutral, $β$-stable deconfined matter limits the mass and the size of quark stars.
A unique parameterization of secondary (thermal) dilepton and photon yields in heavy-ion experiments at CERN-SPS is proposed. Adding those thermal yields to background contributions the spectral shapes of the CERES/NA45, NA38, NA50, HELIOS/3 and WA98 data from experiments with lead and sulfur beams can be well described.
Results of a combined analysis are presented for the production of $ω$ and $ϕ$ mesons in $πN$ reactions in the near-threshold region using throughoutly a conventional ''non-strange'' dynamics based on such processes which are allowed by the non-ideal $ω-ϕ$ mixing. We show that strong interferences of the $t$ (meson exchange) and $s$ and $u$ (nucleon and nucleon resonance) channels differ significantly in $ω$ and $ϕ$ production amplitudes. This leads to a decrease of the relative yields in comparison with expectations based on one-channel models with standard $ω- ϕ$ mixing. We find a strong and non-trivial difference between observables in $ω$ and $ϕ$ production reactions caused by the different role of the nucleon and nucleon resonance amplitudes. A series of predictions for the experimental study of this effect is presented.
The reaction $p n \to d ϕ$ is studied within a covariant boson exchange model. The behavior of polarization observables being accessible in forthcoming experiments near threshold is predicted.
The dependence of the radiative energy loss of fast partons on the initial thermodynamic parameters is studied for deconfined matter to be expected at RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic dependence of the energy loss on the propagated distance leads to a strong increase of the energy loss with increasing initial entropy of deconfined matter supposed its life-time is less than the average time to pass through the medium. This is in contrast to a parameterization with constant energy loss per unit length of propagation. For a sufficiently high initial temperature a two-regime behavior of the energy loss as a function of the initial parton momentum occurs. The angular structure of the energy loss of hard jets with respect to the initial temperature is also discussed for RHIC conditions.
The evolution of strongly interacting matter during the cosmological confinement transition is reviewed. Despite of many proposed relics no specific signal from the rearrangement of quarks and gluons into hadrons has been identified by observations. In contrast to this, several observables in heavy-ion collisions at CERN-SPS energies point to the creation of a matter state near or slightly above deconfinement. We focus here on the analysis of dileptons and direct photons. Similarities and differences of the Big Bang and the Little Bang confinement dynamics are elaborated.
The double differential dilepton spectrum $dN/ (dM_\perp^2 dM^2)$ at fixed transverse mass $M_\perp$ allows a direct access to the vector meson spectral functions. Within a fireball model the sensitivity of $dN/ (dM_\perp^2 dM^2)$ against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum $dN/dM^2$, in the spectrum $dN/dM^2 dM_\perp^2$ with fixed $M_\perp$ the $ω$ signal is clearly seen as bump riding on the $ρ$ background even in case of strong in-medium modifications.
The sequence of phase transitions during the hot history of the universe is followed within a phenomenological framework. Particular emphasis is put on the QCD confinement transition, which is at reach under earth laboratory conditions. A tepid inflationary scenario on the GUT scale with bubble grow at moderate supercooling is discussed.
The data of direct single-photon measurements of the WA98 collaboration in the reaction Pb(158 AGeV) + Pb are analyzed within a thermal model with a minimum number of parameters adjusted to the dilepton data obtained by the CERES and NA50 collaborations in the reactions Pb(158 AGeV) + Au, Pb. The agreement of our model with the WA98 data points to a unique large thermal source emitting electromagnetic radiation observable in both the real and virtual photon channels.
The amplitude of subthreshold phi-meson production is calculated using dominant tree-level diagrams for three-body collisions. It is shown that the production can overwhelmingly be described by two-step processes. The effect of the genuine three-body contribution (i.e. the contribution which cannot be factorized) is discussed. The production rate of phi-mesons is presented for proton induced reactions on carbon.
Extended duality is used to explain the dilepton data of heavy-ion experiments at CERN-SPS. Taking into account the background contributions (hadronic cocktail, Drell-Yan, semileptonic decays of open charm) the spectral shapes of the CERES, NA38/50 and HELIOS-3 data in experiments with lead and sulfur beams can be well described, however, the normalizations of the sulfur beam data are problematic.
A quasiparticle description of the thermodynamics of deconfined matter, reproducing both the perturbative limit and nonperturbative lattice QCD data at finite temperature, is generalized to finite chemical potential. By a flow equation resulting from Maxwell's relation, the equation of state is extended from zero to non-zero quark densities. The impact of the massive strange flavor is considered and implications for cold, charge-neutral deconfined matter in $β$-equilibrium in compact stars are given.
An analysis of the dilepton measurements in the reactions Pb(158 A$\cdot$GeV) + Au, Pb points to a unique thermal source contributing to the invariant mass and transverse momentum spectra. Effects of the flow pattern are discussed.
An effective quasiparticle description of the thermodynamics of deconfined matter, compatible with both finite-temperature lattice data and the perturbative limit, is generalized to finite chemical potential. Within this approach, the available 4-flavor lattice equation of state is extended to finite baryon density, and implications for cold, charge-neutral deconfined matter in beta-equilibrium in compact stars are considered.