Significance of the Sigma Meson in Hadron Physics (QCD) and Possible Experiments to Observe it

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We first discuss the theoretical and phenomenological significance of the sigma meson (σ) in QCD. It is indicated that if the collective modes with the mass 500-600 MeV exists in the I=J=0 channel, various empirical facts in hadron physics can be naturally accounted for, which otherwise would remain mysterious. We propose several experiments to produce and detect the σ in nuclei using nuclear and electro-magnetic projectiles. The recent CHAOS data which show a spectral enhancement near the 2 mπ threshold in the σ channel from the reactions A(π, 2π)A' where A and A' denotes nuclei is interpreted as a possible evidence of a partial restoration of chiral symmetry in nuclei.