S=I=0 Pion Pairs in the A(pi,pi pi)X Reaction
  Recent experimental results show a large enhancement of the 2 pion emission on the scalar isoscalar channel, which had been predicted by some theoretical estimates. We present here a detailed calculation of the A(pi, 2pi)X process incorporating a microscopic model for the elementary reaction in vacuum, pion-pion final state interaction in the nuclear medium, and other nuclear medium effects. 
M. J. Vicente Vacas, E. Oset