Scalar Meson Pairs in Nuclei Experimental Results

The π+A→π+π±A reactions were studied on 2H, 12C, 40Ca and 208Pb nuclei at Tπ+ =283 MeV. Pions were detected in coincidence using the CHAOS spectrometer. The composite ratio CππA between the π+π± invariant masses on nuclei and on the nucleon is presented. Near the 2mπ threshold pion pairs couple to (ππ)I=J=0 when produced in the π+→π+π- reaction channel. There is a marked near-threshold enhancement of Cπ+π-A which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. On the other hand, nuclear matter only weakly influences Cπ+π+A, which displays a flat behaviour throughout the energy range regardless of A. (author)