arXiv subjects

K. Shekhter

Publications and source records attributed to K. Shekhter.

4 recordsLinked to original sources

arXiv2004

Covariant kaon dynamics and kaon flow in heavy ion collisions

The influence of the chiral mean field on the $K^+$ transverse flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the $K^+$ in-plane flow. The FOPI data can be reasonably described using in-medium kaon potentials based on effective chiral models. The information on the in-medium $K^+$ potential extracted from kaon flow is consistent with the knowledge from other sources.

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arXiv2003

Dilepton production in heavy ion collisions at intermediate energies

We present a unified description of the vector meson and dilepton production in elementary and in heavy ion reactions. The production of vector mesons ($ρ,ω$) is described via the excitation of nuclear resonances ($R$). The theoretical framework is an extended vector meson dominance model (eVMD). The treatment of the resonance decays $R\longmapsto NV$ with arbitrary spin is covariant and kinematically complete. The eVMD includes thereby excited vector meson states in the transition form factors. This ensures correct asymptotics and provides a unified description of photonic and mesonic decays. The resonance model is successfully applied to the $ω$ production in $p+p$ reactions. The same model is applied to the dilepton production in elementary reactions ($p+p, p+d$). Corresponding data are well reproduced. However, when the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the experimental dilepton spectra measured by the DLS Collaboration are significantly underestimated at small invariant masses. As a possible solution of this problem the destruction of quantum interference in a dense medium is discussed. A decoherent emission through vector mesons decays enhances the corresponding dilepton yield in heavy ion reactions. In the vicinity of the $ρ/ω$-peak the reproduction of the data requires further a substantial collisional broadening of the $ρ$ and in particular of the $ω$ meson.

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arXiv2002

Off-shell omega production in proton-proton collisions near threshold

The omega production in nucleon-nucleon collisions is described through the decay of intermediate nuclear resonances. Close to threshold the pp --> pp omega cross section is dominated by the off-shell production of omega mesons with masses far below the physical omega mass of 782 MeV. A crucial role plays thereby the N^*(1535) resonance. Due to a strong N omega decay mode this resonance leads to off-shell contributions which are in the vicinity of the threshold about one order of magnitude larger than the experimentally measurable contribution from only the omega peak. After a subtraction of the theoretical "background" from off-shell omega production the available data are accurately reproduced over the entire energy range from very close to threshold up to several GeV above threshold. The scenario of a weaker N^*(1535) --> N omega decay mode which is still consistent with electro- and photo-production data is discussed as well. In the latter case the off-shell contributions to the pp --> pp omega cross section are substantially reduced but the description of the experimental cross section is poor above threshold.

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arXiv2002

The nuclear equation of state probed by K+ production in heavy ion collisions

The dependence of K+ production on the nuclear equation of state is investigated in heavy ion collisions. An increase of the excitation function of K+ multiplicities obtained in heavy (Au+Au) over light (C+C) systems when going far below threshold which has been observed by the KaoS Collaboration strongly favours a soft equation of state. This observation holds despite of the influence of an in-medium kaon potential predicted by effective chiral models which is necessary to reproduce the experimental K+ yields. Phase space effects are discussed with respect to the K+ excitation function.

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