Off-shell effects in s-wave pion absorption

Journal Article · Thu Jun 01 04:00:00 EDT 1978 · Ann. Phys. (N.Y.); (United States)

DOI:https://doi.org/10.1016/S0003-4916(78)80006-2· OSTI ID:6689775

Hachenberg, F; Pirnerdouble-dagger, H J

The effect of s-wave pion absorption on the pion-nucleus optical potential is calculated. We assume absorption by two uncorrelated nucleons with off-shell pion rescattering. For the pion-nucleon interaction we develop a field theoretic model which can be used on- and off-mass shell. A fully relativistic calculation of the pion polarization operator then gives U/sup opt/ =-4..pi..B/sub orho//sup 2/(2..mu..)/sup -1/, with B/sub 0/= (0.094+i0.036) ..mu../sup -4/, as contribution from s-wave absorption to the optical potential. The imaginary part agrees well with the experimentally determined value, while pion dispersion (real part of B/sub o/) does not explain the observed repulsion of the s-wave pion nucleus interaction. We deomonstrate the relevance of oo-shell dynamics in pion-nucleus scattering. The ratio R/sub s/ of ..pi../sup -/-absorption rates by neutron-proton and proton-proton pairs is much smaller than predicted by on-shell models. For equal numbers of neutrons and protons we get R/sub s/approx. =3.0.We also apply the formalism to s-wave pion production in nucleon-nucleon collisions and obtain qualitative agreement with the data. In particular the longstanding puzzle of the small imaginary pion deuteron scattering length compared to Im B/sub 0/ is explained. Our claculation gives Im a/sub pid/=3.7 x 10/sup -3/..mu../sup -1/.

• Research Organization: Institut fuer Theoretische Physik der Universitaet, D-6900 Heidelberg, Germany
• OSTI ID: 6689775
• Journal Information: Ann. Phys. (N.Y.); (United States), Journal Name: Ann. Phys. (N.Y.); (United States) Vol. 112:2; ISSN APNYA
• Country of Publication: United States
• Language: English

Related Subjects

653003* -- Nuclear Theory-- Nuclear Reactions & Scattering
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CHARGED-PARTICLE REACTIONS
HADRON REACTIONS
HADRON-HADRON INTERACTIONS
INTERACTIONS
MESON REACTIONS
MESON-BARYON INTERACTIONS
MESON-NUCLEON INTERACTIONS
NUCLEAR POTENTIAL
NUCLEAR REACTIONS
OPTICAL MODELS
ORIENTATION
PARTIAL WAVES
PARTICLE INTERACTIONS
PARTICLE PRODUCTION
PION REACTIONS
PION-DEUTERON INTERACTIONS
PION-NUCLEON INTERACTIONS
S WAVES
SCATTERING LENGTHS
SPIN ORIENTATION