Effects of nuclear correlations on low-energy pion charge-exchange scattering

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Abstract
An isospin-invariant optical-potential framework is used to make a coordinated analysis of low-energy pion elastic and single- and double-charge-exchange scattering to isobaric analog states. The form of the potential studied here is motivated by the work of Stricker, McManus, and Carr, who emphasized the importance of isoscalar absorption-dispersive and correlation effects for low-energy pion elastic scattering. In this paper we examine the influence of the corresponding isovector and isotensor nuclear correlations on low-energy charge exchange. Comparison of our results to 50 MeV data supports the existence of the isovector correlation terms, but shows a need for an additional isotensor effect. A distorted-wave Born approximation analysis confirms that distortions are weak (the mean density of interaction is roughly 50% of the central value), but demonstrates that distortions of the pion waves by the nuclear medium cannot be neglected in describing charge exchange.