Measurement of the sup 12 C(. pi. ,2. pi. ) reactions and possible evidence of a double-. Delta. excitation

Cross sections, pion momentum spectra, and angular distributions for the reactions {sup 12}C({pi}{sup {minus}},{pi}{sup +}{pi}{sup {minus}}) and {sup 12}C({pi}{sup {minus}},2{pi}{sup {minus}}) at a bombarding energy of 292 MeV were measured wth a 360{degree} spectrometer. An enhancement of the cross-section ratio of {sup 12}C({pi}{sup {minus}},2{pi}{sup {minus}}) to {sup 12}C({pi}{sup {minus}},{pi}{sup +}{pi}{sup {minus}}) relative to that of the elementary cross sections was observed, and is discussed in terms of various nuclear-medium effects including a double-{Delta} production channel.