INFLUENCE OF NUCLEAR-STRUCTURE ON THE CHARACTERISTICS OF LIGHT PIONICATOMS

An extended version of the standard pion-nucleus optical potential is presented using the momentum-space formulation of the multiple scatter ing theory. This potential is used for studying the influence of nonlo cal effects and nuclear structure on the characteristics of light pion ic atoms. A method is suggested to treat the long-range two-nucleon co rrelations involved in the second-order optical potential. Particularl y, the spin-orbital Fermi motion correction to the first-order optical potential, the center-of-mass correlations, and the spin-isospin corr ections to the second-order optical potential are discussed in some de tail. The results are presented in comparison with the experimental da ta for the 1s and 2p levels of light pionic atoms up to Ca-44.