UBC Theses and Dissertations

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UBC Theses and Dissertations

Low energy elastic scattering and the pionic atom anomaly Hanna, Mark


Differential cross sections for the elastic scattering of low energy (20 MeV) positive and negative pions from ¹²C and ⁴⁰Ca have been measured. This measurement was performed at TRIUMF using the QQD low energy pion spectrometer at 11 angles between 45° and 125°. The π⁺ ¹²C data are in good agreement with [OBG⁺83], as are the π⁻ ¹²C data with [WBB+87], indicating that the overall normalization of the cross sections is good. However, the π± ⁴⁰Ca data do not agree well with the previously published data of [WMR+88]. An optical potential model, whose parameters were determined from pionic atom data, was used to predict these differential cross sections. Two sets of parameters were used in the model. One set was determined from fits to "normal" pionic atom data, while another set was extracted from fits to "anomalous" data where level shifts and widths do not compare to theoretical values obtained when the normal set of parameters is used. In all the above cases, the experimental data best fits the optical model predictions of [FG80,Fri88b] when the normal set of parameters is used. The qualitative agreement of the data to the "normal" optical model predictions indicates that the pionic anomaly effects do not extend to positive pion energy values.

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