Measurement of Pion Double Charge Exchange on Carbon-13, Carbon-14, Magnesium-26, and Iron-56

摘要

Cross sections for the /sup 13,14/C, sup 26 Mg, sup 56 Fe( pi exp + , pi exp - )/sup 13,14/O, sup 26 Si, sup 56 Ni reactions were measured with the Energetic Pion Channel and Spectrometer at the Clinton P. Anderson Meson Physics Facility for 120 less than or equal to T/sub pi / less than or equal to 292 MeV and 0 less than or equal to theta less than or equal to 50. The double isobaric analog states (DIAS) are of primary interest. In addition, cross sections for transitions to sup 14 O(0 exp + , 5.92 MeV), sup 14 O(2 exp + , 7.77 MeV), sup 56 Ni(gs), sup 13 O(gs), and sup 13 O(4.21 MeV) are presented. The exp 13 O(4.21 MeV) state is postulated to have J/sup pi / = 1/2 exp - . The data are compared to previously measured double-charge-exchange cross sections on other nuclei, and the systematics of double charge exchange on T greater than or equal to 1 target nuclei leading to the DIAS are studied. Near the delta sub 33 resonance, cross sections for the DIAS transitions are in disagreement with calculations in which the reaction is treated as sequential charge exchange through the free pion-nucleon amplitude, while for T/sub pi / > 200 MeV the anomalous features of the 164 MeV data are not apparent. This is evidence for significant higher order contributions to the double-charge-exchange amplitude near the reasonable energy. Two theoretical approaches that include two nucleon processes are applied to the DIAS data. 64 references. (ERA citation 10:024756)