The influence of the nuclear medium on K+ total cross sections

doi:10.1016/0370-2693(93)90222-4

Physics Letters B

Volume 307, Issues 3–4, 17 June 1993, Pages 293-297

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Abstract

The study of the K⁺ total cross sections on a wide range of nuclei has revealed important modifications of the free-space K⁺-nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on ⁶Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.

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K+-nucleus potentials from K+-nucleon amplitudes
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Optical potentials for $K^{+}$ -nucleus interactions are constructed from $K^{+}$ -nucleon amplitudes using recently developed algorithm based on $K^{+}$ -N kinematics in the nuclear medium. With the deep penetration of $K^{+}$ mesons into the nucleus at momenta below $800 MeV / c$ it is possible to test this approach with greater sensitivity than hitherto done with $K^{-}$ and pions. The energy-dependence of experimental reaction and total cross sections on nuclei is better reproduced with this approach compared to fixed-energy amplitudes. The inclusion of Pauli correlations in the medium also improves the agreement between calculation and experiment. The absolute scale of the cross sections is reproduced very well for ⁶Li but for C, Si and Ca calculated cross sections are ( $23 \pm 4$ )% smaller than experiment, in agreement with earlier analyses. Two phenomenological models that produce such missing strength suggest that the imaginary part of the potential needs about 40% enhancement.
In-medium nuclear interactions of low-energy hadrons
2007, Physics Reports
Exotic atoms provide a unique laboratory for studying strong interactions and nuclear medium effects at zero kinetic energy. Experimental and theoretical developments of the last decade in the study of exotic atoms and some related low-energy reactions are reviewed. The exotic atoms considered are of $π^{-}, K^{-}, \bar{p}, Σ^{-}$ , and also the so far unobserved $Ξ^{-}$ atoms. The analysis of these atomic systems consists of fitting density-dependent optical potentials $V_{opt} = t (ρ) ρ$ to comprehensive sets of data of strong-interaction level shifts, widths and yields across the periodic table. These provide information on the in-medium hadron–nucleon t matrix $t (ρ)$ over a wide range of densities up to central nuclear densities. For pions, the review focuses on the extraction of the $π N$ in-medium s-wave interaction from pionic atoms, which include also the deeply bound $π^{-}$ atomic states recently observed at GSI in isotopes of Sn and Pb. Also included are recent measurements at PSI of elastic scattering of $π^{\pm}$ on Si, Ca, Ni and Zr at 21.5 MeV. The experimental results are analyzed in the context of chirally motivated $π$ -nuclear potentials, and the evidence for partial restoration of chiral symmetry in dense nuclear matter is critically discussed. For antikaons, we review the evidence from $K^{-}$ atoms, and also from low-energy $K^{-} p$ scattering and reaction data for and against a deep $\bar{K}$ -nucleus potential of 150–200 MeV attraction at nuclear matter density. The case for relatively narrow deeply bound $K^{-}$ atomic states is made, essentially independent of the potential-depth issue. Recent experimental suggestions from KEK and DA $Φ$ NE (Frascati) for signals of $\bar{K}$ -nuclear deeply bound states are reviewed, and dynamical models for calculating binding energies and widths of $\bar{K}$ -nuclear states are discussed. For kaons we review the evidence, from $K^{+}$ total and reaction cross section measurements at the AGS (BNL) on Li, C, Si and Ca at $p_{lab} = 500 - 700 MeV / c$ , for significant absorptivity of $t_{KN} (ρ)$ beyond that expected from $t_{KN}^{free}$ within the impulse approximation. Attempts to explain the extra absorptivity for the relatively weak interaction of K mesons in terms of a hypothetical exotic $S =+ 1$ pentaquark $Θ^{+}$ strength are reviewed. For antiprotons the exceptionally broad data base due to the recent results of the PS209 collaboration at CERN are analyzed, together with results of radiochemical experiments. We discuss the dependence of the phenomenological $\bar{p}$ -nucleus interaction on the model adopted for the neutron density, showing how the neutron densities favored by our comprehensive analysis are compatible with densities from other sources, including our own analysis of pionic atoms. It is also shown how the strong absorptivity of the $\bar{p}$ -nucleus interaction, which leads to the prediction of saturation of widths in deeply bound $\bar{p}$ -atom states, also explains the observed saturation effects in low-energy $\bar{p}$ annihilation on nuclei. For $Σ$ hyperons we review the evidence, from continuum $Σ^{-}$ hypernuclear $(π^{-}, K^{+})$ spectra obtained recently at KEK on C, Si, Ni, In and Bi, for substantial repulsion in the $Σ$ -nucleus interaction, and the relationship to the inner repulsion established earlier from the density-dependence analysis of $Σ^{-}$ atoms and by analyses of past $(K^{-}, π^{\pm})$ AGS experiments.
Lastly, for $Ξ$ hyperons we review prospects of measuring X-ray spectra in $Ξ^{-}$ atoms and thereby extracting meaningful information on the $Ξ$ -nucleus interaction. The significance of the latter to the physics of $Λ Λ$ hypernuclei and to extrapolation into multistrange hypernuclei are briefly reviewed.
The effect of the in-medium Θ+ pentaquark on the kaon optical potential
2006, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The kaon nuclear optical potential is studied including the effect of the $Θ^{+}$ pentaquark. The one-nucleon contribution is obtained using an extension of the Jülich meson-exchange potential as bare kaon–nucleon interaction. Significant differences between a fully self-consistent calculation and the usually employed low-density Tρ approach are observed. The influence of the one-nucleon absorption process, $K N \to Θ^{+}$ , on the kaon optical potential is negligible due to the small width of the pentaquark. In contrast, the two-nucleon mechanism, $K N N \to Θ^{+} N$ , estimated from the coupling of the pentaquark to a two-meson cloud, provides the required amount of additional kaon absorption to reconcile with data the systematically low $K^{+}$ -nucleus reaction cross sections found by the theoretical models.
The K+-nucleus cross sections in relativistic non-linear models
2003, Nuclear Physics A
The K⁺−nucleus cross sections have been calculated in relativistic non-linear models taking into account the in-medium modifications of nucleons and mesons properties. More precisely, we have taken into account both the dressing of the nucleon effective mass by the scalar nuclear field in the target and the coupling of the mesons exchanged between the K⁺ and the nucleons to the polarization of the medium. First, using the most recent relativistic non-linear models, the in-medium σ, ω and ρ meson masses have been obtained in the nuclear matter rest frame. The influence of the non-linear contributions on the K⁺−nucleus cross sections has then been studied. Finally, we have compared our results with the experimental data.
K±-mesons as probes for observing some "EMC"-like effect
2001, Nuclear Physics A
Unconventional medium effect in K+-nucleus scattering
1998, Nuclear Physics A

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^☆: This work was performed under the auspices of the US Department of Energy (DE-AC02-76CH00016) and assistance was obtained from the US-Israel Binational Science Foundation.

^∗: We have benefited greatly by the provision of calculations by W.R. Gibbs, P.B. Siegel and W.B. Kaufmann, as well as discussions with them and with C.B. Dover and Avraham Gal. We also wish to acknowledge the contributions of our technical staff: J. Rutherford, E. Meier, A. Minn, G. Sheffer and M. Zilka.

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Physics Letters B

Abstract

References (14)

Phys. Rep.

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K<sup>+</sup>-nucleus potentials from K<sup>+</sup>-nucleon amplitudes

In-medium nuclear interactions of low-energy hadrons

The effect of the in-medium Θ<sup>+</sup> pentaquark on the kaon optical potential

The K<sup>+</sup>-nucleus cross sections in relativistic non-linear models

K±-mesons as probes for observing some "EMC"-like effect

Unconventional medium effect in K<sup>+</sup>-nucleus scattering

The influence of the nuclear medium on K+ total cross sections☆

Abstract

Phys. Rep.

Nucl. Phys. A

Phys. Rev. C

Phys. Rev. C

Phys. Rev. Lett.

Phys. Rev. C

Phys. Rev. C

Phys. Rev. D

The influence of the nuclear medium on K⁺ total cross sections☆