Scalar meson pairs in nuclei experimental results

The pi (+)A --> pi (+)pi (+/-)A' reactions were studied on H-2, C-12, Ca-40 and (208)pb nuclei at Tpi+ = 283 MeV. Pions were detected in coincidence u sing the CHAOS spectrometer. The composite ratio C-pi pi(A) between the pi (+)pi (+/-) invariant masses on nuclei and on the nucleon is presented. Nea r the 2m(pi) threshold pion pairs couple to (pi pi)(I=J=0) when produced in the pi (+) --> pi (+)pi (-) reaction channel. There is a marked near-thres hold enhancement of C-pi+pi-(A) which is consistent with theoretical predic tions addressing the partial restoration of chiral symmetry in nuclear matt er. On the other hand, nuclear matter only weakly influences C-pi+pi+(A), w hich displays a flat behaviour throughout the energy range regardless of A.