V. S. Uma Maheswari

In-medium dependence and Coulomb effects of the pion production in heavy ion collisions

Abstract The properties of the high energy pions observed in heavy ion collisions, in particular in the system Au on Au at 1 GeV/nucleon are investigated. The reaction dynamics is described within the Quantum Molecular Dynamics (QMD) approach. It is shown that high energy pions freeze out early and originate from the hot, compressed matter. N * -resonances are found to give an important contribution toward the high energy tail of the pion. Further the role of in-medium effects in the description of charged pion yields and spectra is investigated using a microscopic potential derived from the Brueckner G -matrix which is obtained with the Reid soft-core potential. It is seen that the high energy part of the spectra is relatively more suppressed due to in-medium effects as compared to the low energy part. A comparison to experiments further demonstrates that the present calculations describe reasonably well the neutral (TAPS) and charged (FOPI) pion spectra. The observed energy dependence of the π − / π + ratio, i.e. deviations from the isobar model prediction, is due to Coulomb effects and again indicate that high energy pions probe the hot and dense phase of the reaction. These findings are confirmed independently by a simple phase space analysis.

Role of the Coulomb interaction in the flow and the azimuthal distribution of kaons from heavy ion reactions

Coulomb final-state interaction of positive charged kaons in heavy ion reactions and its impact on the kaon transverse flow and the kaon azimuthal distribution are investigated within the framework of QMD (quantum molecular dynamics) model. The Coulomb interaction is found to tend to draw the flow of kaons away from that of nucleons and lead to a more isotropic azimuthal distribution of kaons in the target rapidity region. The recent FOPI data have been analyzed by taking into account both the Coulomb interaction and a kaon in-medium potential of the strong interaction. Although the effect of the kaon Coulomb potential on the kaon flow and azimuthal distribution is much smaller than that of the strong potential, it is found to be visible, and therefore, should be taken into account if one wants to extract unambiguous information about the kaon strong potential in nuclear matter from the kaon flow and azimuthal distribution data.

Role of isospin dependent mean field in pion production in heavy ion reactions

The importance of an isospin dependent nuclear mean field (IDMF) in regard to the pion production mechanism is studied for the reaction Au+Au at 1 GeV/nucleon using the quantum molecular dynamics (QMD) model. In particular, the effect of the IDMF on pion spectra and the charged pion ratio are analyzed. It is found that the inclusion of a IDMF considerably suppresses the low-

Origin of subthreshold K+ production in heavy ion collisions

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Origin of subthresholdK+production in heavy ion collisions

pions, thus leading to a better agreement with the data on pion spectra. Moreover, the rapidity distribution of the charged pion ratio appears to be sensitive to the isospin dependence of the nuclear mean field.

Origin of subthreshold K{sup +} production in heavy ion collisions

We investigate the origin of subthreshold K+ production in heavy ion collisions at intermediate energies. In particular we study the influence of the pion induced K+ creation processes. We find that this channel shows a strong dependence on the size of the system, i.e., the number of participating nucleons as well as on the incident energy of the reaction. In an energy region between 1 and 2 GeV/nucleon the pion induced processes essentially contribute to the total yield and can even become dominant in reactions with a large number of participating nucleons. Thus we are able to reproduce recent measurements of the KaoS Collaboration for 1 GeV/nucleon Au on Au reactions adopting a realistic momentum dependent nuclear mean field.

Reply to Comment on Influence of bulk properties on the surface structure of finite nuclei

We investigate the origin of subthreshold K+ production in heavy ion collisions at intermediate energies. In particular we study the influence of the pion induced K+ creation processes. We find that this channel shows a strong dependence on the size of the system, i.e., the number of participating nucleons as well as on the incident energy of the reaction. In an energy region between 1 and 2 GeV/nucleon the pion induced processes essentially contribute to the total yield and can even become dominant in reactions with a large number of participating nucleons. Thus we are able to reproduce recent measurements of the KaoS Collaboration for 1 GeV/nucleon Au on Au reactions adopting a realistic momentum dependent nuclear mean field.

Radial flow of kaon mesons in heavy ion reactions

We investigate the origin of subthreshold K+ production in heavy ion collisions at intermediate energies. In particular we study the influence of the pion induced K+ creation processes. We find that this channel shows a strong dependence on the size of the system, i.e., the number of participating nucleons as well as on the incident energy of the reaction. In an energy region between 1 and 2 GeV/nucleon the pion induced processes essentially contribute to the total yield and can even become dominant in reactions with a large number of participating nucleons. Thus we are able to reproduce recent measurements of the KaoS Collaboration for 1 GeV/nucleon Au on Au reactions adopting a realistic momentum dependent nuclear mean field.

Anisotropy of subthreshold K+ emission in heavy ion reactions

In reply to the preceding Comment, it is found that the present results regarding the dependence of the surface thickness on the Fermi momentum agree with that of the Comment. However, we differ with the conclusions of the preceding Comment.