Strangeness Saturation: Dependence on System-Size, Centrality and Energy
The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic heavy-ion collisions.
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arXiv subjects
B. Kampfer
Publications and source records attributed to B. Kampfer.
From QCD lattice calculations to the equation of state of quark matter
We describe two-flavor QCD lattice data for the pressure at finite temperature and zero chemical potential within a quasiparticle model. Relying only on thermodynamic selfconsistency, the model is extended to nonzero chemical potential. The results agree with lattice calculations in the region of small chemical potential.
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Strangeness Saturation: Energy- and System-Size Dependence
Relativistic heavy-ion collisions lead to a final state which has a higher degree of strangeness saturation than those of elementary collisions. A systematic analysis of this phenomenon, based on the strangeness saturation factor, is made for C+C, Si+Si and Pb+Pb collisions at the CERN SPS collider and for Au+Au collisions at RHIC energies. Strangeness saturation is shown to increase with the number of participants within a colliding system, at both CERN SPS and RHIC energies. The saturation observed in central collisions of lighter nuclei deviates from that seen in peripheral collisions of heavier nuclei with an equivalent participant number, which could be due to the difference in nuclear density.
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In-medium spectral change of omega mesons as a probe of QCD four-quark condensate
Within QCD sum rules at finite baryon density we show the crucial role of four-quark condensates for the in-medium modification of the omega meson spectral function. In particular, such a global property as the sign of the in-medium omega meson mass shift is found to be governed by a parameter which describes the strength of the density dependence of the four-quark condensate beyond mean-field approximation. To study self-consistently the broadening of the omega meson resonance we employ a hadron spectral function based on the omega meson propagator delivered by an effective chiral Lagrangian. Measurements of the omega meson spectral change in heavy-ion collisions with the HADES detector can reveal the yet unknown density dependence of the four-quark condensate.
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Tagging the p n -> d phi reaction by backward protons in p d -> d phi p_{sp} processes
The reaction p d -> d phi p_{sp} is studied within the Bethe-Salpeter formalism. Under special kinematical conditions (slow backward spectator proton p_{sp} and fast forward deuteron) relevant for forthcoming experiments at COSY, the cross section and a set of polarization observables factorize in the contribution of the pure subprocess p n -> d phi and a contribution stemming from deuteron quantities and kinematical factors. This provides a theoretical basis for studying threshold-near processes at quasi-free neutrons.
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Relativistic effects in proton-induced deuteron break-up at intermediate energies with forward emission of a fast proton pair
Recent data on the reaction pD -> (pp) n with a fast forward pp pair with very small excitation energy is analyzed within a covariant approach based on the Bethe-Salpeter formalism. It is demonstrated that the minimum non-relativistic amplitude is completely masked by relativistic effects, such as Lorentz boost and the negative-energy P components in the 1S_0 Bethe-Salpeter amplitude of the pp pair.
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Quasi-particle model for deconfined matter
Our quasi-particle model for deconfined matter near T_c is reviewed. The extrapolation of lattice QCD data to a finite baryo-chemical potential is discussed. Determined by the chiral transition temperature T_c, the resulting equation of state of neutral and beta-stable deconfined matter is soft and limits size and mass of pure quark stars.
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Baryon Resonance Dynamics in pi N \to N V Reactions Near Threshold
The rho - omega interference in the exclusive reaction pi N \to N' e+ e- is studied within a schematic model including the established baryon resonances up to 1720 MeV. Near threshold the interference can be used to separate the isoscalar part of the electromagnetic current. The role of various baryon resonances is highlighted.
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Exclusive charge exchange reaction pD->n(pp) within the Bethe-Salpeter formalism
The exclusive charge exchange reaction pD->n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final state interaction in the detected pp pair at nearly zero excitation energy is described by the 1S0 component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential cross-section persuade that, as in the non-relativistic case, this reaction (i) can be utilized as a ``relativistic deuteron polarimeter'' and (ii) delivers further information about the elementary nucleon-nucleon charge-exchange amplitude.
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Probing the strange quark condensate by di-electrons from phi meson decays in heavy-ion collisions at SIS energies
QCD sum rules predict that the change of the strange quark condensate $<\bar s s>$ in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from $ϕ$ meson decays. Due to the expansion of hadron matter in heavy-ion collisions, the $ϕ$ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as effective broadening of the di-electron spectrum in the $ϕ$ region. The emerging broadening is sensitive to the in-medium change of $<\bar s s>$. This allows to probe directly in-medium modifications of $<\bar s s>$ via di-electron spectra in heavy-ion collisions at SIS energies with HADES.
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Final State Interaction within the Bethe-Salpeter Approach in Charge Exchange pD->n(pp) process
The exclusive charge exchange reaction pD->n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final state interaction in the detected at zero-near excitation energy pp-pair is described by the 1S0 component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential cross-section persuade that, as in the non relativistic case, this reaction can be utilized for a relativistic deuteron tensor polarimeter and as a source of information about the elementary nucleon-nucleon charge exchange amplitude.
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Towards strangeness saturation in central heavy-ion collisions at high energies
Analyses of the centrality binned identified hadron multiplicities at SPS and RHIC within the statistical-thermal model point to strangeness saturation with increasing centrality and energy.
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Energy loss of quarks in deconfined matter at RHIC: photon-tagged jets, single electron and dilepton spectra from open charm
We report a first attempt (i) to derive constraints on the energy loss of charm quarks in a deconfined medium from the recent PHENIX data of single-electron transverse momentum spectra and (ii) to estimate the resulting suppression of dileptons from correlated semi-leptonic decays of open charmed mesons. The momentum imbalance of photon-tagged light-quark jets is also considered.
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Evaluation of QCD sum rules for light vector mesons at finite density and temperature
QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of mass parameters for the lightest vector mesons $ρ$, $ω$ and $ϕ$ in a strongly interacting medium. For conditions relevant for the starting experiments at HADES we find that the in-medium mass shifts of the $ρ$ and $ω$ mesons are governed, within the Borel QCD sum rule approach, by the density and temperature dependence of the four-quark condensate. In particular, the variation of the strength of the density dependence of the four-quark condensate reflects directly the decreasing mass of the $ρ$ meson and can lead to a change of the sign of the $ω$ meson mass shift as a function of the density. In contrast, the in-medium mass of the $ϕ$ meson is directly related to the chiral strange quark condensate which seems correspondingly accessible.
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Thermal Parameters in Heavy Ion Collisions at SPS and RHIC: Centrality Dependence
The centrality dependence of thermal parameters describing hadron multiplicities and intermediate-mass dilepton spectra in heavy-ion collisions at SPS and RHIC is analyzed. From experimental hadron multiplicities we deduce evidence for strangeness saturation at high energy and maximum centrality. The observed dilepton spectra can be parameterized by a centrality independent temperature.
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Evaluation of QCD sum rules for HADES
QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of pole mass parameters for the lightest vector mesons $ρ$, $ω$ and $ϕ$ in a strongly interacting medium at conditions relevant for the starting experiments at HADES. The role of the four-quark condensate is highlighted. A few estimates (within a fire ball model and BUU calculations) of dilepton spectra in heavy-ion collisions at 1 AGeV are presented.
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Centrality dependence of thermal parameters in heavy-ion collisions at SPS and RHIC
We analyze the centrality dependence of thermal parameters describing hadron multiplicities, hadron spectra and dilepton spectra in heavy-ion collisions at SPS and RHIC energies.
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Production of phi mesons in subthreshold heavy-ion collisions
Within a BUU type transport model we study $ϕ$ meson production in subthreshold Ni+Ni and Ru+Ru reactions. For the first time we included in our model the elementary reaction channels $ρ+N,Δ\to ϕ+N$, $π+N(1520) \to ϕ+N$ and $πρ$ $\to$ $ϕ$. In spite of a substantial increase of the $ϕ$ multiplicities by these channels our results stay significantly below the preliminary experimental data.
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