Local field corrections in. pi. -nucleus scattering
The local field correction to the ..pi..-nucleus optical potential is calculated taking recoil into account. The correction arises from the triple scattering matrix element <0;k vertical-bartau/sub 1/Gtau/sub 2/Gtau/sub 1/vertical-bar 0;k'>, where tau/sub i/ are ..pi..N amplitudes. The recoil energy of nucleon 1 affects the pion Green's function G and the intermediate scattering amplitude tau/sub 2/. The recoil of nucleon 2 affects only tau/sub 2/ and has not been included to save computational time. Effects of antisymmetry of the two nucleons, spin flip, and charge exchange have been included, but not those of pair correlation and Pauli blocking. Inclusion of recoil is found to reduce the local field correction by a factor of 7 from the result of fixed scatterer calculations. Nevertheless, the local field correction remains sizable. In the ..pi..-/sup 16/O case it represents a correction 2/3 as large as the first-order optical potential near the ..pi..N resonant energy. Nucleon 1 typically recoils through approx. 1 fm while in terms of the internucleon separation r/sub 12/ the effect is very long ranged. Thus the P-wave nature of the ..pi..N interaction which enhances the reflection of the pion from nucleon 2 back to nucleon 1 is the main reason why the local field correction is so important in ..pi..-nucleus scattering. The imaginary part of the local field correction part of the optical potential is analyzed and its reactive content is shown to arise from two competing mechanisms. The first, and dominant, mechanism is a reduction of the single nucleon knockout contribution that is overestimated in the first-order optical potential while the second mechanism is the two-nucleon knockout. The analysis suggests very slow convergence of multiple scattering expansions near the ..pi..N resonance energy.
- Research Organization:
- Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742
- OSTI ID:
- 5446556
- Journal Information:
- Phys. Rev., C; (United States), Vol. 21:5
- Country of Publication:
- United States
- Language:
- English
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PION REACTIONS
ELASTIC SCATTERING
CHARGE-EXCHANGE REACTIONS
GREEN FUNCTION
KNOCK-OUT REACTIONS
MATRIX ELEMENTS
MULTIPLE SCATTERING
NUCLEAR REACTION KINETICS
OPTICAL MODELS
OXYGEN 16 TARGET
P WAVES
RECOILS
SCATTERING AMPLITUDES
SPIN FLIP
TOTAL CROSS SECTIONS
AMPLITUDES
CHARGED-PARTICLE REACTIONS
CROSS SECTIONS
DIRECT REACTIONS
FUNCTIONS
HADRON REACTIONS
KINETICS
MESON REACTIONS
NUCLEAR REACTIONS
PARTIAL WAVES
REACTION KINETICS
SCATTERING
TARGETS
653003* - Nuclear Theory- Nuclear Reactions & Scattering
651315 - Nuclear Properties & Reactions
A=6-19
Theoretical- Nuclear Reactions & Scattering- (-1987)