Pion induced quasi-elastic knockout reactions on carbon

In an experiment performed at S.I.N. we have shown that a coincidence measurement of the (π,π,p) reaction yields a wealth of information on the pion nucleus interaction. Our most prominent findings are: (1) Inside the carbon nucleus, the width of the (3,3) resonance is reduced by about a factor of 2, and (2) its position is shifted downward by approximately 10 MeV. (3) The ratio d sigma (π+, π+, p) d sigma (π-, π-, p) in the region Ex < 9.75 MeV is approximately 12 in disagreement with current theoretical predictions. (4) There is no more than a 2% probability for coherent charge exchange between the 12C and 11B nuclei for the reactions 12C(π +-:π +-,p)11B for the kinematic region studied. (5) The ratio d sigma (π-:π-,d) d sigma (π-:π-d) on 12C is unity as expected from isospin conservation. (6) The ratio d sigma (π+; π+, t) d sigma (π-; π-, t) on 12C is also unity, indicating that these events are the result of a primary (π; π, d) reaction followed by a neutron pickup reaction. (7) The PWIA has only limited success in describing the experimental results. It can predict the general shape of the momentum distribution of the scattered pions, including the number of peaks and their relative heights. It fails to reproduce their widths and exact position. The normalization constant needed to make the theory agree with the data is dependent on the beam energy, the observation angles and the momentum range of the scattered pions. However, the averages of the normalization constants for all runs at a particular incident beam energy agree with each other approximately, except at 160 MeV where it is a factor of 2 smaller. (8) Because the effective incident energy which gave the best fit between theory and data varied with the experimental parameters, we have been unable to draw any conclusion on the off-shell πp differential cross-section