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In-medium isovector piN amplitude from low-energy pion scattering.
E Friedman1, M Bauer, J Breitschopf
1Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel. elifried@vms.huji.ac.il
Physical Review Letters
|September 28, 2004
Summary
Researchers studied pion-nucleus interactions at 21.5 MeV, observing anomalous repulsion in s-wave scattering. This repulsion, seen in silicon, calcium, nickel, and zirconium, is explained by a chiral model modifying the pion decay constant.
Area of Science:
- Nuclear Physics
- Particle Physics
Background:
- Pion-nucleus interactions are crucial for understanding nuclear structure.
- Pionic atoms exhibit anomalous repulsion in s-wave interactions.
- The pion-nucleus potential is sensitive to the nuclear medium.
Purpose of the Study:
- Investigate pion-nucleus potential using elastic scattering.
- Explore the "anomalous" repulsion observed in s-wave scattering.
- Test chiral-motivated models for pion-nucleus interactions.
Main Methods:
- Measured differential cross sections for elastic scattering of 21.5 MeV positive and negative pions.
- Used silicon (Si), calcium (Ca), nickel (Ni), and zirconium (Zr) targets.
- Analyzed scattering data to determine the pion-nucleus potential.
Main Results:
- Observed "anomalous" repulsion in the s-wave term for pion scattering.
- This anomaly is consistent with observations in pionic atoms.
- The observed repulsion could be explained by a chiral model with a modified pion decay constant in the medium.
Conclusions:
- The "anomalous" repulsion in pion-nucleus scattering is a significant phenomenon.
- Chiral-motivated models provide a framework for understanding this anomaly.
- Empirical on-shell energy dependence alone does not resolve the anomaly, unlike in pionic atoms.