TY - JOUR
T1 - In-medium nuclear interactions of low-energy hadrons
AU - Friedman, E.
AU - Gal, A.
PY - 2007/11
Y1 - 2007/11
N2 - 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-, over(p, -), Σ-, and also the so far unobserved Ξ- atoms. The analysis of these atomic systems consists of fitting density-dependent optical potentials Vopt = 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± 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 deepover(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 DAΦNE (Frascati) for signals of over(K, -)-nuclear deeply bound states are reviewed, and dynamical models for calculating binding energies and widths of over(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 atplab = 500 - 700 MeV / c, for significant absorptivity of tKN (ρ) beyond that expected from tKNfree 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 over(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 over(p, -)-nucleus interaction, which leads to the prediction of saturation of widths in deeply bound over(p, -)-atom states, also explains the observed saturation effects in low-energy over(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±) 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.
AB - 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-, over(p, -), Σ-, and also the so far unobserved Ξ- atoms. The analysis of these atomic systems consists of fitting density-dependent optical potentials Vopt = 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± 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 deepover(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 DAΦNE (Frascati) for signals of over(K, -)-nuclear deeply bound states are reviewed, and dynamical models for calculating binding energies and widths of over(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 atplab = 500 - 700 MeV / c, for significant absorptivity of tKN (ρ) beyond that expected from tKNfree 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 over(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 over(p, -)-nucleus interaction, which leads to the prediction of saturation of widths in deeply bound over(p, -)-atom states, also explains the observed saturation effects in low-energy over(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±) 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.
KW - Density dependence
KW - Exotic atoms
KW - In-medium interactions
KW - Optical potential
KW - Strong interaction
UR - http://www.scopus.com/inward/record.url?scp=35148878799&partnerID=8YFLogxK
U2 - 10.1016/j.physrep.2007.08.002
DO - 10.1016/j.physrep.2007.08.002
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AN - SCOPUS:35148878799
SN - 0370-1573
VL - 452
SP - 89
EP - 153
JO - Physics Reports
JF - Physics Reports
IS - 4-5
ER -