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HK: Physik der Hadronen und Kerne

HK 40: Theorie V

HK 40.9: Talk

Wednesday, March 24, 1999, 17:30–17:45, A

Signature of the In-Medium ππ Mass Modification in the (π, 2π) Knockout Reaction off Nuclei — •Z. Aouissat and J. Wambach — Institut für Kernphysik, TU-Darmstadt.

The present status of the in-medium ππ mass distribution in the scalar-isoscalar channel around the threshold is reviewed from the theory side and contrasted with recent experimental results of CHAOS collaboration on the (π,2π) knock-out reactions off nuclei. The strongly target-mass dependent invariant mass enhancement of the two pions at threshold reported by the CHAOS collaboration

[1] F. Bonutti et al., Phys. Rev. Lett. 77 (4) 603 (1996). indicates a clear departure from the usual physics observed in the same knock-out reactions off bare nucleons. A simple explanation to this phenomena can be attributed to the in-medium renormalisation of correlated pion-pairs, which strongly reshapes the density of states for the π−π rescattering in the final state interaction. Since the dynamics of pions is dictated by chiral symmetry and its breaking, a special attention is paid to the non-perturbative treatment of the π−π correlations.