Near-threshold (p-arrow-right,. pi. /sup -/) reactions on calcium isotopes

Cross section and analyzing power angular distribution measurements are reported for the /sup 48/Ca(p-arrow-right,..pi../sup -/) /sup 49/Ti reaction at two bombarding energies (T/sub p/ = 166 and 205 MeV) and for /sup 42/Ca(p-arrow-right,..pi../sup -/) /sup 43/Ti at T/sub p/ = 205 MeV. Also presented for comparison are single-angle spectra for (p,..pi../sup -/) on other f/sub 7/2/-shell targets and for /sup 48/Ti(p,..pi../sup +/) /sup 49/Ti. The (p, ..pi../sup -/) spectra show a strong selectivity for population of high-spin ((15/2)/sup -/ and (19/2)/sup -/) 2p-1h ((..pi..f/sub 7/2/)/sup 2/(..nu..f/sub 7/2/)/sup -1/) states, which are not prominent in the (p,..pi../sup +/) spectrum. Supporting evidence for the high-spin identification comes from comparisons with simple (p,..pi../sup -/) model calculations and the results of other reaction studies. Characteristic features of the data for the high-spin states and for the continuum portions of the (p,..pi../sup -/) spectra are discussed in the context of a two-nucleon (NN..-->..NN..pi..) pion production mechanism. All of the main systematic features observed are at least qualitatively consistent with expectations for such a mechanism.