First Measurement of Antikaon Phase-Space Distributions in Nucleus-Nucleus Collisions at Subthreshold Beam Energies

Differential production cross sections of K$^-$ and K$^+$ mesons have been measured as function of the polar emission angle in Ni+Ni collisions at a beam energy of 1.93 AGeV. In near-central collisions, the spectral shapes and the widths of the rapidity distributions of K$^-$ and K$^+$ mesons are in agreement with the assumption of isotropic emission. In non-central collisions, the K$^-$ and K$^+$ rapidity distributions are broader than expected for a single thermal source. In this case, the polar angle distributions are strongly forward-backward peaked and the nonisotropic contribution to the total yield is about one third both for K$^+$ and K$^-$ mesons. The K$^-$/K$^+$ ratio is found to be about 0.03 independent of the centrality of the reaction. This value is significantly larger than predicted by microscopic transport calculations if in-medium modifications of K mesons are neglected.Comment: 16 pages, 3 figures, accepted for publication in Physics Letters

Towards an orientation of higher education in the post Rio+20 process: How is the game changing?

The purpose of this paper is to identify and assess the implications of sustainable development for the future orientation of higher education, especially after the 2012 United Nations Conference on Sustainable Development (Rio + 20). A qualitative trend analysis is being used for this purpose, in the context of which three macro trends are combined: (1) higher education that has been developed via five periods; (2) sustainable development that has evolved through three stages; and (3) the nexus between sustainable development and higher education which has strengthened through three phases. The simultaneous analysis of the macro trends regarding their possible interactive effects (through an expert panel discussion) demonstrates that higher education and universities under the influence of sustainable development elements are entering into a new era in which the function of “higher education for sustainable development” could be interpreted as the seeds of a newly emerging mission for universities. In this regard, it is expected that the concept of “sustainable university” is likely to become more common to meet the emerging mission. Consistent with the Rio + 20 outcomes, the authors analyzed the concept of “sustainable university” and identified the fact that it is practically divided into three interrelated and complementary categories, namely social-, environmental-, and economic-oriented university in pursuit of actualizing sustainable development

Influence of Impact Parameter on Thermal Description of Relativistic Heavy Ion Collisions at GSI/SIS

Attention is drawn to the role played by the size of the system in the thermodynamic analysis of particle yields in relativistic heavy ion collisions at SIS energies. This manifests itself in the non-linear dependence of K+ and K- yields in $AA$ collisions at 1 -- 2 A.GeV on the number of participants. It is shown that this dependence can be quantitatively well described in terms of a thermal model with a canonical strangeness conservation. The measured particle multiplicity ratios (pi+/p, pi-/pi+, d/p, K+/pi+ and K+/K- but not eta/pi0) in central Au-Au and Ni-Ni collisions at 0.8 -- 2.0 A.GeV are also explained in the context of a thermal model with a common freeze-out temperature and chemical potential. Including the concept of collective flow a consistent picture of particle energy distributions is derived with the flow velocity being strongly impact-parameter dependent.Comment: revtex, 20 figure

Nonequilibrium Weak Processes in Kaon Condensation I --- Reaction rate for the thermal kaon process ---

We investigate the thermal kaon process,in which kaons are thermally produced via nucleon-nucleon collisions.This process is relevant to nonequilibrium dynamics of kaon condensation inside neutron stars.The reaction rates for these processes are calculated, and their temperature and density dependences are compared with those of other reaction rates.It is shown that the thermal kaon process is dominant over other relevant weak reactions throughout the nonequilibrium process, such as the kaon-induced Urca and the modified Urca reactions, and may control the entire evolution of the kaon condensate. The characteristic role of the soft and hard kaons during the evolution is explained, and implications for astrophysical phenomena are briefly discussed.Comment: 31 pages,incl.10 eps figures,RevTe

Nonequilibrium Weak Processes in Kaon Condensation II - Kinetics of condensation ---

The kinetics of negatively charged kaon condensation in the early stages of a newly born neutron star is considered. The thermal kaon process, in which kaons are thermally produced by nucleon-nucleon collisions, is found to be dominant throughout the equilibration process. Temporal changes of the order parameter of the condensate and the number densities of the chemical species are obtained from the rate equations, which include the thermal kaon reactions as well as the kaon-induced Urca and the modified Urca reactions. It is shown that the dynamical evolution of the condensate is characterized by three stages: the first, prior to establishment of a condensate, the second, during the growth and subsequent saturation of the condensate, and the third, near chemical equilibrium. The connection between the existence of a soft kaon mode and the instability of the noncondensed state is discussed. Implications of the nonequilibrium process on the possible delayed collapse of a protoneutron star are also mentioned.Comment: 27 pages, incl. 8 eps figures, RevTe

Current correlation functions, QCD sum rules and vector mesons in baryonic matter

Based on an effective Lagrangian which combines chiral SU(3) dynamics with vector meson dominance, we have developed a model for the forward vector meson-nucleon scattering amplitudes. We use this as an input to calculate the low energy part of the current-current correlation function in nuclear matter. Its spectrum enters directly in the ``left hand side'' of QCD sum rules. For the isovector channel we find a significant enhancement of the in-medium spectral density below the rho resonance while the rho meson mass itself changes only slightly. The situation is different in the isoscalar channel, where the mass and peak position of the omega meson move downward while its width increases less drastically than in the rho meson case. For the phi meson we find almost no mass shift; the width of the peak broadens moderately. We observe a remarkable degree of consistency with the operator product expansion of QCD sum rules in all three channels. We point out, however, that these results cannot simply be interpreted, as commonly done, in terms of a universal rescaling of vector meson masses in matter.Comment: 40 pages, LaTeX 2e,10 figures in eps , submitted to Nucl.Phys.

Medium Effects in Kaon and Antikaon Production in Nuclear Collisions at Subthreshold Beam Energies

Production cross sections of K$^+$ and K$^-$ mesons have been measured in C+C collisions at beam energies per nucleon below and near the nucleon-nucleon threshold. At a given beam energy, the spectral slopes of the K$^-$ mesons are significantly steeper than the ones of the K$^+$ mesons. The excitation functions for K$^+$ and K$^-$ mesons nearly coincide when correcting for the threshold energy. In contrast, the K$^+$ yield exceeds the K$^-$ yield by a factor of about 100 in proton-proton collisions at beam energies near the respective nucleon-nucleon thresholds.Comment: Accepted for publication in Phys. Rev. Let

Chiral unitary theory: application to nuclear problems

In this talk we briefly describe some basic elements of chiral perturbation theory, $\chi PT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $\pi \pi$ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $\phi$ meson properties are changed in a nuclear medium.Comment: 15 pages, 9 figures, Invited talk in the International Symposium on Nuclear Physics, Bombay, december 200

Branching ratio change in K- absorption at rest and the nature of the Lambda(1405)

We investigate in-medium corrections to the branching ratio in K- absorption at rest and their effect on the (positively and negatively) charged pion spectrum. The in-medium corrections are due to Pauli blocking, which arises if the Lambda(1405) is assumed to be a $\bar{K}$-nucleon bound state and leads to a density and momentum dependent mass shift of the Lambda(1405). Requiring that the optical potential as well as the branching ratio are derived from the same elementary T-matrix, we find that the in-medium corrected, density dependent T-matrix gives a better description of the K- absorption reaction than the free, density-independent one. This result suggests that the dominant component of the Lambda(1405) wave function is the $\bar{K}N$ bound state.Comment: 8 Pages, Revtex with epsf, and embedded 8 ps figure

Chiral dynamics of baryon resonances and hadrons in a nuclear medium

In these lectures I make an introduction to chiral unitary theory applied to the meson baryon interaction and show how several well known resonances are dynamically generated, and others are predicted. Two very recent experiments are analyzed, one of them showing the existence of two $\Lambda(1405)$ states and the other one providing support for the $\Lambda(1520)$ resonance as a quasibound state of $\Sigma(1385) \pi$. The use of chiral Lagrangians to account for the hadronic interaction at the elementary level introduces a new approach to deal with the modification of meson and baryon properties in a nuclear medium. Examples of it for $\bar{K}$, $\eta$ and $\phi$ modification in the nuclear medium are presented.Comment: Lectures given in the Workshop on Hadron Physics, Puri (India), march 200