The $\sigma$ meson in a nuclear medium through two pion photoproduction

Abstract

We present theoretical results for $(\gamma ,{\pi }^0{\pi }^0)$ production on nucleons and nuclei in the kinematical region where the scalar isoscalar $\pi \pi$ amplitude is influenced by the $\sigma$ pole. The final state interaction of the pions modified by the nuclear medium produces a spectacular shift of strength of the two pion invariant mass distribution induced by the moving of the $\sigma$ pole to lower masses and widths as the nuclear density increases.

14 pages, 7 figures

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