Search results for "Optical potential"
showing 10 items of 16 documents
The effect of the in-medium Θ+ pentaquark on the kaon optical potential
2005
The kaon nuclear optical potential is studied including the effect of the $\Theta^+$ pentaquark. The one-nucleon contribution is obtained using an extension of the J\"ulich meson-exchange potential as bare kaon-nucleon interaction. Significant differences between a fully self-consistent calculation and the usually employed low-density $T\rho$ approach are observed. The influence of the one-nucleon absorption process, $K N \to \Theta^+$, on the kaon optical potential is negligible due to the small width of the pentaquark. In contrast, the two-nucleon mechanism, $K N N \to \Theta^+ N$, estimated from the coupling of the pentaquark to a two-meson cloud, provides the required amount of addition…
Nonlocalities and Fermi motion corrections in K- atoms
2002
We evaluate the p-wave $K^-N$ amplitudes from the chiral Lagrangians and from there construct the p-wave part of the $K^-$ nucleus optical potential plus a small s-wave part induced from the elementary p-wave amplitude and the nuclear Fermi motion. Simultaneously, the momentum and energy dependence of the s-wave optical potential, previously developed, are taken into account and shown to generate a small p-wave correction to the optical potential. All the corrections considered are small compared to the leading s-wave potential, and lead to changes in the shifts and widths which are smaller than the experimental errors. A thorough study of the threshold region and low densities is conducted…
Neutron distributions from pionic atoms
1992
Abstract The radii of neutron distributions in nuclei are extracted from experimental shifts and widths of pionic atoms. A best fit to pionic-atom data is carried out by varying simultaneously the neutron radii and the parameter of a pion-nucleus optical potential. We have used three different potentials: one of them theoretical plus a small phenomenological part, another one semiphenomenological, with the linear terms in the density obtained from experimental πN amplitudes and the quadratic terms fitted to the pionic-atom data, and a third one purely phenomenological, obtained from a direct fit to pionic-atom data. The radii obtained with all of them are remarkably close and also close to …
Deeply bound levels in kaonic atoms
2000
Using a microscopic antikaon-nucleus optical potential recently developed by Ramos and Oset (nucl-th/9906016, in print in Nuclear Physics A) from a chiral model, we calculate strong interaction shifts and widths for $K^-$ atoms. This purely theoretical potential gives an acceptable description of the measured data ($\chi^2/{\rm num.data}= 3.8$), though it turns out to be less attractive than what can be inferred from the existing kaon atomic data. We also use a modified potential, obtained by adding to the latter theoretical one a s-wave term which is fitted to known experimental kaonic data ($\chi^2/{\rm degree of freedom}= 1.6$), to predict deeply bound $K^-$ atomic levels, not detected y…
Radiative kaon capture on nuclei.
1990
Hypernuclear formation through the radiative capture of in-flight ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ is studied in a distorted wave impluse approximation approach. The elementary operator is obtained from first-order Feynman diagrams and is constrained by the reactions ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma} and, via crossing, by \ensuremath{\gamma}p\ensuremath{\rightarrow}${\mathit{K}}^{+}$\ensuremath{\Lambda}. The ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ distortion has been included via a simple optical potential which is in agreement with ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ elastic scattering on nuclei. Using the…
Transmission of ultra-cold neutrons through guides coated with materials of high optical potential
2014
Abstract We have measured the transmission of ultra-cold neutrons (UCN) through tubes coated on the inside with materials of high optical potentials. The best transmission value, T, normalised to 1 m long UCN guides was obtained with a beryllium coated quartz guide, T=(99.0±1.0)%. Furthermore, excellent transmission coefficients were found for (i) a glass tube coated with NiMo(88/12), T=(97.3 ±0.6)%, (ii) a NiMo(85/15) guide made by the replication technique, T=(97.1 ±0.8)% and (iii) a glass guide coated with NiMo(82/18), T=(96.3 ±2.1)%. The results demonstrate that UCN guides made from coated glass tubes have the same excellent transmission properties as those produced with the replication…
Coherent and incoherent η-photoproduction from nuclei
1991
Abstract Elastic and inelastic η-photoproduction from complex nuclei is studied in a distorted-wave impulse approximation (DWIA) framework. The elementary operator is obtained by using a dynamical model which employs the reactions π N→ π N, π N→ ππ N and π − p→ η n to fix the hadronic vertex as well as the isobar propagators and the process γ N→ π N to constrain the electromagnetic vertex. The nuclear structure input for the inelastic transitions has been extracted from electron-scattering form factors. The η final-state interaction has been included via a simple optical potential using the ηN t -matrix as an input. We find that coherent η-production is dominated by the D 13 (1520) isobar w…
A theoretical approach to pionic atoms and the problem of anomalies
1993
Abstract We have constructed a theoretical optical potential for pionic atoms based on the first- and second-order terms of a many-body expansion on the number of ph excitations. The p-wave parts are very much influenced by the medium polarization. The quenching at large densities produced by this phenomenon, together with the one from the Lorentz-Lorenz effect, and modifications over standard potentials due to the isospin dependence, lead to a new potential which produces notoriously improved results in the problem of anomalies. A clearer definition of this problem is proposed as the inability of standard potentials to reproduce simultaneously the data for light and heavy nuclei. Finally a…
The (K-, p) reaction on nuclei with in-flight kaons
2010
10th International Conference on Hypernuclear and Strange Particle Physics. Tokai, JAPAN, SEP 14-18, 2009
eta nucleus optical potential in a chiral unitary approach
2002
The self-energy of an eta in a nuclear medium is calculated in a chiral unitary model, and applied to eta states in nuclei. Our calculation predicts an attractive eta nucleus optical potential which can accommodate many eta bound states in different nuclei.