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Register a new userOn the widths and binding energies of $K^-$ nuclear states and the role of $K^-$ multi-nucleon interactions
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We report on our recent self-consistent calculations of $K^-$ nuclear quasi-bound states using $K^-$ optical potentials derived from chirally motivated meson-baryon coupled channels models [1,2]. The $K^-$ single-nucleon potentials were supplemented by a phenomenological $K^-$ multi-nucleon interaction term introduced to achieve good fits to $K^-$ atom data. We demonstrate a substantial impact of the $K^-$ multi-nucleon absorption on the widths of $K^-$ nuclear states. If such states ever exist in nuclear many-body systems, their widths are excessively large to allow observation.
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We demonstrate that the binding energies and widths of eta-mesic nuclei depend strongly on subthreshold eta-N interaction. This strong dependence is made evident from comparing three different eta-nucleus optical potentials: (1) a microscopic optical potential taking into account the full effects of off-shell eta-nucleon interactions; (2) a factorization approximation to the microscopic optical potential where a downward energy shift parameter is introduced to approximate the subthreshold eta-nucleon interaction; and (3) an optical potential using on-shell eta-nucleon scattering length as the interaction input. Our analysis indicates that the in-medium $eta$N interaction for bound-state formation is about 30 MeV below the free-space $eta$N threshold, which causes a substantial reduction of the attractive force between the $eta$ and nucleon with respect to that implied by the scattering length. Consequently, the scattering-length approach overpredicts the binding energies and caution must be exercised when these latter predictions are used as guide in searching for $eta$-nucleus bound states. We also show that final-state-interaction analysis cannot provide an unequivocal determination of the existence of $eta$-nucleus bound state. More direct measurements are, therefore, necessary.
We investigate the K^- ^3He and K^+ K^- interactions in the reaction pd -> ^3He K^+ K^- near threshold and compare our model calculations with data from the MOMO experiment at COSY-Juelich. A large attractive effective K^- p amplitude would give a significant K^- ^3He final-state interaction effect which is not supported by the experimental data. We also estimate upper limits for the a_0(980) and f_0(980) contributions to the produced K^+ K^- pairs.
Total and reaction cross sections are derived self consistently from the attenuation cross sections measured in transmission experiments at the AGS for K^+ on Li^6, C, Si and Ca in the momentum range of 500-700 MeV/c by using a V_{opt}=t_{eff}(rho)rho optical potential. Self consistency requires, for the KN in-medium t matrix, that Im t_{eff}(rho) increases linearly with the average nuclear density in excess of a threshold value of 0.088+-0.004 fm^-3. The density dependence of Re t_{eff}(rho) is studied phenomenologically, and also applying a relativistic mean field approach, by fitting the integral cross sections. The real part of the optical potential is found to be systematically less repulsive with increasing energy than expected from the free-space repulsive KN interaction. When the elastic scattering data for Li^6 and C at 715 MeV/c are included in the analysis, a tendency of Re V_{opt} to generate an attractive pocket at the nuclear surface is observed.
The invariant mass spectra of $phi to K^{+}K^{-}$ are measured in 12 GeV $p+A$ reactions in order to search for the in-medium modification of $phi$ mesons. The observed $K^{+}K^{-}$ spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three $betagamma$ regions between 1.0 and 3.5. The nuclear mass-number dependence of the yields of the $K^{+}K^{-}$ decay channel is compared to the simultaneously measured $e^{+}e^{-}$ decay channel for carbon and copper targets. We parameterize the production yields as $sigma (A) = sigma_0 times A^alpha$ and obtain $alpha_{phito K^+K^-} - alpha_{phito e^+e^-}$ to be 0.14 $pm$ 0.12. Limits are obtained for the partial decay widths of $phi$ mesons in nuclear matter.
Nuclear mass contains a wealth of nuclear structure information, and has been widely employed to extract the nuclear effective interactions. The known nuclear mass is usually extracted from the experimental atomic mass by subtracting the masses of electrons and adding the binding energy of electrons in the atom. However, the binding energies of electrons are sometimes neglected in extracting the known nuclear masses. The influence of binding energies of electrons on nuclear mass predictions are carefully investigated in this work. If the binding energies of electrons are directly subtracted from the theoretical mass predictions, the rms deviations of nuclear mass predictions with respect to the known data are increased by about $200$ keV for nuclei with $Z, Ngeqslant 8$. Furthermore, by using the Coulomb energies between protons to absorb the binding energies of electrons, their influence on the rms deviations is significantly reduced to only about $10$ keV for nuclei with $Z, Ngeqslant 8$. However, the binding energies of electrons are still important for the heavy nuclei, about $150$ keV for nuclei around $Z=100$ and up to about $500$ keV for nuclei around $Z=120$. Therefore, it is necessary to consider the binding energies of electrons to reliably predict the masses of heavy nuclei at an accuracy of hundreds of keV.
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