Download or read book Contributions of Pair Correlations to Pion-nucleus Double Charge Exchange written by and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recognizing the importance of both the reaction mechanism and nuclear structure aspects of the DCX, a new reaction theory was proposed in 1981 which offers a consistent treatment of these two equally important components of pion DCX. In this theory, the density square-dependent interaction is derived from the dynamical consideration of true pion absorption on a nucleon pair inside the nucleus. The strength of this new pion-nucleus interaction can then be calculated from the knowledge of the second-order pion-nucleus optical potential. With no free parameters for the pion-nucleus interaction and with the use of the coexistence nuclear model, the theory gives satisfactory descriptions of the magnitude and the shape of 5° excitation functions as well as of the differential cross sections for the DCX reactions 18O(.pi., .pi.−) 18Ne(DIAS) and 42Ca(.pi., .pi.−) 42Ti(DIAS) between 120 and 290 MeV. Our basic conclusions are: (1) the TSSCX mechanism alone cannot describe pion DCX; (2) the position of the first minimum in the differential cross section is very sensitive to the inclusion of density square-dependent interaction; and (3) on the other hand, the magnitude of the cross section is very sensitive to the inclusion of pair correlations (core excitation in the case with 18O and 42Ca).