Pion induced pion production in nuclei

The process of pion-induced pion production in nuclei has been studied with the A(π+,π+π-) and A(π+,π+π-p) reactions for four nuclei 2H, 12C, 40Ca, and 208Pb at an incident pion energy of Tπ+=283 MeV. The π+π- and π+π-p particles in the final state were detected in coincidence with the CHAOS spectrometer at TRIUMF. By looking at kinematic quantities such as missing momentum and missing energy, we have been able to draw some model-independent conclusions about the dynamics of the π→ππ process in nuclei, which do not vary significantly with target mass. We find that the incident pion interacts mainly with one surface nucleon via the leading πN→ππN channel. The pion pair releases no appreciable energy to the residual nucleus, which remains substantially bound throughout the reaction. These findings underline the quasifree nature of the pion production reaction in nuclei.