Abstract
We try to find an improved phenomenological optical potential for pionic atoms in two steps. First, we perform a new fit of the parameters in the standard optical potentials by using a large data base of 140 pionic atom data. A χ 2 is obtained that is substantially lower than with any previous parameter set. In a second step, we extend the number of parameters by using a more general form for the terms quadratic in the nuclear density. This extended version yields a reduction of the χ 2 by about a factor of two. The new fit includes a good description of shifts and widths of the deeply bound 3d orbits in heavy nuclei such as 181Ta, natRe, natPt, 197Au, 208Pb and 209Bi. The value of the additional parameters in the extended version are difficult to interpret in the context of the chosen form of the optical potential and indicate that higher-order effects play a role.
Published Version
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