arXiv subjects
Publications and source records attributed to B. Kampfer.
Utilizing the QCD sum rule approach to the behavior of the omega meson in nuclear matter we derive evidence for in-medium changes of particular four-quark condensates from the recent CB-TAPS experiment for the reaction gamma + A -> A' + omega (-> pi0 gamma) with A = Nb and LH2.
We analyze an effect of the coherent $Θ^+Λ(1520)$ photoproduction in $γD$ interaction near the threshold. We demonstrate that the coherence effect becomes manifest in a comparison of the $nK^+$ invariant mass distribution when the $pK^-$ invariant equals the $Λ(1520)$ mass. Our model calculations indicate a sizeable contribution of resonant and non-resonant background processes in the $γD\to np K^+K^-$ reaction which generally exceed the contribution of the coherent resonant channel. However, we find that the coherent $Θ^+Λ(1520)$ photoproduction is enhanced relative to the background processes in the forward hemisphere of the $pK^-$ pair photoproduction. Moreover, the coherence effect does not depend on the $Θ^+$ photoproduction amplitude and is defined by the probabilities of the $Λ(1520)$ photoproduction and the $Θ^+\to NK$ transition. Therefore, this coherence effect may be used as an independent method for studying the mechanism of $Θ^+$ production and $Θ^+$ properties.
We analyze two types of spin observables in the reaction $π\vec D\to\vecΣΘ^+$ near the threshold. One concerns the spin-transfer coefficients $K_x^x$ and $K_z^z$. The second one is the deuteron spin anisotropy. These observables are sensitive to the $Θ^+$ parity and can be used as a tool for the $Θ^+$ parity determination.
The successful quasi-particle model is compared with recent lattice data of the coefficients in the Taylor series expansion of the excess pressure at finite temperature and baryon density. A chain of approximations, starting from QCD to arrive at the model expressions for the entropy density, is presented.
The QCD sum rule approach to in-medium modifications of the omega meson in nuclear matter is reviewed with emphasis of its relation to 4-quark condensates and chiral symmetry restoration. Possible implications of the CB-TAPS experiment for the reaction gamma A -> A' omega (-> pi0 gamma) are sketched and the particularly important role of di-electron probes, accessible with HADES, is highlighted. A brief update of a parametrization of the previous dilepton and photon probes from CERES and WA98 of heavy-ion collisions at CERN-SPS energies is presented.
We present a description of the equation of state of strongly interacting matter within a quasi-particle model. The model is adjusted to lattice QCD data near the deconfinement temperature $T_c$. We compare in detail the excess pressure at non-vanishing chemical potential and its expansion coefficients with two-flavor lattice QCD calculations and outline prospects of the extrapolation to large baryon density.
Strangeness and charm degrees of freedom in strongly interacting matter are discussed within a quasi-particle model adjusted to lattice QCD data. The model allows to extrapolate lattice QCD data to large baryo-chemical potential. We outline the thermal evolution of matter in the early universe at and slightly after confinement and comment briefly on charm dynamics in relativistic heavy-ion collisions.
We investigate the splitting and mixing of $ρ$ and $ω$ mesons in nuclear matter. The calculations were performed on the basis of QCD sum rules and include all operators up to mass dimension-6 twist-4 and up to first order in the coupling constants. Special attention is devoted to the impact of the scalar 4-quark condensates on both effects. In nuclear matter the Landau damping governs the $ρ- ω$ mass splitting while the scalar 4-quark condensates govern the strenght of individual mass shifts. A strong in-medium mass splitting causes the disappearance of the $ρ- ω$ mixing.
We analyse the centrality dependence of thermal parameters deduced from hadron m ultiplicities in Au + Au collisions at $\sqrt{s_{NN}} = 130 GeV$. While the chemical freeze-out temperature and chemical potentials are found to be roughly centrality-independent, the strangeness saturation factor $γ_S$ increases with participant number towards unity, supporting the assumption of equilibrium freeze-out conditions in central collisions.
Vector meson ($V = ω, ϕ$) production in near-threshold elementary nucleon-nucleon collisions $pp\to ppV$, $pn\to pnV$ and $pn\to dV$ is studied within an effective meson-nucleon theory. It is shown that a set of effective parameters can be established to describe fairly well the available experimental data of angular distributions and the energy dependence of the total cross sections without explicit implementation of the Okubo-Zweig-Iisuka rule violation. Isospin effects are considered in detail and compared with experimental data whenever available.
We present a unique parameterization of the equation of state of strongly interacting matter in the temperature interval 0.6 T_c ... 3 T_c at μ= 0 within a quasi-particle model based on quark and gluon degrees of freedom. The extension to non-vanishing baryon-chemical potential is discussed.
K+, K- and ϕmeson production in proton-nucleus (pA) collisions has been calculated within a BUU transport model. It is shown that the nucleon-hyperon strangeness transfer channel is essential. The role of three-body reactions has been investigated within the medium. The targetmass dependence of $ϕ$ production is predicted to give important information on the in-medium properties of all three mesons.
The lowest-order induced soft gluon radiation processes of heavy quarks have been analyzed to quantify the dead cone effect. This effect is most likely expected to suppress significantly the energy loss of charm quarks passing an amorphous color-neutral deconfined medium, as has been concluded from recent experiments at RHIC.
The production of the light vector mesons $V = ρ, ω, ϕ$ in the reactions $πN \to V N$ and $N N \to V N N$ near threshold is studied. The subsequent electromagnetic decay $V \to γ^* \to e^+ e^-$ is particularly suited for exploring subthreshold $ωN$ resonances.
We review our quasiparticle model for the thermodynamics of strongly interacting matter at high temperature, and its extrapolation to non-zero chemical potential. Some implications of the resulting soft equation of state of quark matter at low temperatures are pointed out.
We present a combined analysis of the in-medium behavior of rho and omega mesons within the Borel QCD sum rule taking into account finite widths.
Within the Borel QCD sum rule approach at finite baryon density we study the role of the four-quark condensates for the modifications of the vector mesons $ρ$, $ω$ and $ϕ$ in nuclear matter. We find that in-medium modifications of the $ρ$ and $ω$ mesons are essentially dominated by the dependence of the 4-quark condensate on the nucleon density. In particular, the numerical value of a parameter ($κ_N$), which describes the strength of the density dependence of the 4-quark condensate beyond the mean-field approximation, governs the decrease of the $ρ$ mass as a function of the density. For the $ω$ meson the sign of the in-medium mass shift is changed by variations of $κ_N$. To study consistently the in-medium broadening of the light vector mesons we employ $ρN$ and $ωN$ scattering amplitudes derived recently from a covariant unitary coupled channel approach adjusted to pion- and photo-induced reactions. In contrast to the $ρ$ and $ω$ mesons, the in-medium mass of the $ϕ$ meson is directly related to the chiral (strange) quark condensate. Measurements of the vector meson spectral change in heavy-ion collisions with HADES can shed light on the yet unknown density dependence of the 4-quark condensate.
Within a transport code simulation for heavy-ion collisions at bombarding energies around 1 AGeV, we demonstrate that double-differential di-electron spectra with suitable kinematical cuts are useful to isolate (i) the $ρ$ meson peak even in case of strong broadening, and (ii) the in-medium $ω$ decay contribution. The expected in-medium modifications of the vector meson spectral densities can thus be probed in this energy range via the di-electron channel.