In-Medium $\pi -\pi$ Correlations in the '$\sigma$-Meson'-Channel

Abstract

The present status of the in-medium invariant $\pi -\pi$ mass distribution in the sigma-meson channel around the threshold is reviewed from the theory side and contrasted with recent experiments on $(\pi ,2\pi )$ knock-out reactions. A preliminary investigation indicates that the strongly target-mass dependent invariant mass enhancement of the two pions can be explained theoretically. A more refined reaction theory is needed to confirm this result. In the theoretical description, based on the linear sigma model, emphasis is put on constraints from chiral symmetry.

Comments: 11 pages, Latex, 5 figures