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B. Kämpfer

Publications and source records attributed to B. Kämpfer.

83 records · Page 5Linked to original sources
arXiv2000

Production of ϕMesons in Near-Threshold πN and N N Reactions

We analyze the production of $ϕ$ mesons in $πN$ and NN reactions in the near-threshold region, using throughout the conventional ``non-strange'' dynamics based on such processes which are allowed by the non-ideal $ω-ϕ$ mixing. We show that the occurrence of the direct $ϕNN$ interaction may show up in different unpolarized and polarization observables in $πN\to Nϕ$ reactions. We find a strong non-trivial difference between observables in the reactions $pp\to ppϕ$ and $pn\to pnϕ$ caused by the different role of the spin singlet and triplet states in the entrance channel. A series of predictions for the experimental study of this effect is presented.

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arXiv2000

Solar Proton Burning Process Revisited within a Covariant Model Based on the Bethe-Salpeter Formalism

A covariant model based on the Bethe-Salpeter formalism is proposed for investigating the solar proton burning process $pp\to De^+ν_e$ and the near-threshold deuteron disintegration via electromagnetic and weak interactions. Results of numerical calculations of the energy dependence of relevant cross sections and the astrophysical low-energy cross section factor $S_{pp}$ of the proton burning process are presented. Our results confirm previous canonical values, and the energy dependence of the $S_{pp}$ factor is rather close to phenomenological extrapolations commonly adopted in computations of solar nuclear reaction rates.

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arXiv1998

The reaction NN \to NN ϕnear threshold

The sensitivity of polarization observables in the reaction $NN \to NN ϕ$ slightly above the threshold is studied with respect to the details of the one-boson exchange model and a possible admixture of hidden strangeness in the nucleon. It is shown that the finite-energy predictions differ strongly from the threshold predictions. A measurement of the beam - target asymmetry and the $ϕ$ decay anisotropy can help to disentangle the role of various reaction mechanisms.

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arXiv1998

Thermal dilepton signal versus dileptons from open charm and bottom decays in heavy-ion collisions

We analyze the opportunity to observe thermal dileptons emitted off deconfined matter resulting in heavy-ion collisions at RHIC and LHC energies. Special kinematical conditions provided by the detector systems PHENIX and ALICE, and the so-called $M_\perp$ scaling behavior of thermal dilepton spectra are taken into account. Our considerations include energy loss effects of the fast heavy quarks in deconfined matter, which for themselves can help to identify the creation of a hot and dense parton medium. Due to a threshold like effect for decay leptons we find a window at large transverse pair momentum and fixed transverse mass where the thermal signal can exceed the background of dileptons from correlated semileptonic decays of charm and bottom mesons.

hep-ph↗
arXiv1998

Thermodynamics of the ϕ^4 theory in tadpole approximation

Relying on the Luttinger-Ward theorem we derive a thermodynamically selfconsistent and scale independent approximation of the thermodynamic potential for the scalar $ϕ^4$ theory in the tadpole approximation. The resulting thermodynamic potential as a function of the temperature is similar to the one of the recently proposed screened perturbation theory.

hep-ph↗
arXiv1997

Estimates of dilepton spectra from open charm and bottom decays

The spectra of lepton pairs from correlated open charm and bottom decays in ultrarelativistic heavy-ion collisions are calculated. Our approach includes energy loss effects of the fast heavy quarks in deconfined matter which are determined by temperature and density of the expanding parton medium. We find a noticeable suppression of the initial transverse momentum spectrum of heavy quarks due to the energy loss within the central rapidity covered by the PHENIX detector system. As a result the dilepton yields from correlated decays of heavy quarks are in the same order of magnitude as the Drell-Yan signal.

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arXiv1997

Estimates of dilepton spectra from open charm and bottom decays in relativistic heavy-ion collisions

The spectra of lepton pairs from correlated open charm and bottom decays in ultrarelativistic heavy-ion collisions are calculated. Our approach includes energy loss effects of heavy quarks in deconfined matter which are determined by temperature and density of the expanding parton medium. We find a noticeable suppression of the initial transverse momentum spectrum of heavy quarks due to the energy loss at LHC conditions. Within the central rapidity covered by the ALICE detector system, the dominant contribution from bottom decays to the high invariant mass dielectron spectrum is predicted.

hep-ph↗
arXiv1997

Bremsstrahlung in intermediate-energy nucleon reactions within an effective one-boson exchange model

Within a covariant effective one-boson exchange model for the $T$ matrix of $NN$ interactions we present detailed calculations of bremsstrahlung cross sections for proton - proton and proton - neutron reactions at beam energies in the 1 GeV region. Besides pure bremsstrahlung processes we consider photons from $Δ$ decays and contributions from the $η\to γγ$ process. At beam energies above 700 MeV the $Δ$ decay channel dominates the spectra at large photon energies, where the interference between non-resonance processes and the $Δ$ decay channel becomes also important. Low energy photons stem from pure bremsstrahlung processes. The available experimental data at 730 MeV beam energy is well described. We extrapolate the model down to 280 MeV, where more detailed experimental data exist, and find agreement with angular distributions.

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arXiv1997

Polarization observables in the reaction $NN \to NN Φ$

We study the reaction $NN \to NN Φ$ slightly above the threshold within an extended one-boson exchange model which also accounts for $uud$ knock-out. It is shown that polarization observables, like the beam-target asymmetry, are sensible quantities for identifying a $s \bar s$ admixture in the nucleon wave function on the few per cent level.

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