The pi -> pi pi process in nuclei and the restoration of chiral symmetry
  The results of an extensive campaign of measurements of the pi -> pi pi process in the nucleon and nuclei at intermediate energies are presented. The measurements were motivated by the study of strong pi pi correlations in nuclei. The analysis relies on the composite ratio C_{pi pi}^A, which accounts for the clear effect of the nuclear medium on the (pi pi) system. The comparison of the C_{pi pi}^A distributions for the (pi pi)_{I=J=0} and (pi pi)_{I=0,J=2} systems to the model predictions indicates that the C_{pi pi}^A behavior in proximity of the 2m_pi threshold is explainable through the partial restoration of chiral symmetry in nuclei. 
N. Grion, M. Bregant, P. Camerini, E. Fragiacomo, S. Piano, R. Rui,   E.F. Gibson, G. Hofman, E.L. Mathie, R. Meier, M.E. Se...