Results on pi /sup -/p backward elastic scattering and search for pi /sup -/p to dp at 9 and 12 GeV/c

From an experiment done with the CERN Omega spectrometer, triggered by a fast forward proton device, results on the differential cross section d sigma /du for pi /sup -/p backward elastic scattering are presented. The d sigma /du distribution agrees with an Ae/sup BU/ law. The compilation of existing results shows a discrepancy between results but the (d sigma /du)/sub u=0/ data fit perfectly on s/sup 2 alpha 0-2/ dependence, as predicted by a single Delta /sub delta / Regge trajectory exchange. A search for the reaction pi /sup -/p to dp, with a fast forward deuteron, which can be produced by a double- baryon exchange mechanism, gives cross-section upper limits of approximately 1% of the backward elastic cross section. (10 refs)