Spin flip effects in pion-nucleus interactions

The authors investigate the effect of spin flip in the reaction mechanism of pion-nucleus interactions, theoretically and experimentally. They construct the microscopic optical potential in configuration space from first principles, summing particle-hole pair contributions. Subsequently, they solve the coupled-channel Klein-Gordon equation including spin flip and Fermi averaging corrections. They calculate the transition matrix elements for elastic, inelastic and charge exchange scattering. They compare and contrast to previous models with the aid of a code, based on the formalism as described. In addition, they analyze the experimental spectra obtained for the double charge exchange reaction 93Nb(π+, π-)93Tc at a scattering angle of 5 degrees and three beam energies, Tπ = 164, 230, 294 MeV, with emphasis on a particular class of states (T<) below the double isobaric analog state. The excitation function of the T< states cannot be understood without the participation of spin flip in the reaction mechanism. From the theoretical and experimental analysis the authors conclude that spin flip is an important component of the reaction mechanism in the scattering of pions from nuclei