Positive-pion absorption by C nuclei at 130 MeV

Abstract

About 1500 absorption events of π+ in flight (∼ 130 MeV of kinetic energy) have been studied in a propane bubble chamber. The corresponding cross-section is (189 ± 19) mb/C nucleus, about one half of the total inelastic cross-section. The absorption on two nucleons with low excitation of the residual nucleus seems to be responsible for 10% of the σtot abs only, while the capture by an α-cluster seems to be more important (∼40% of the total). The events have been analysed according to their charged-prong multiplicity. Data concerning two-prong events agree with the theoretical predictions calculated by assuming the dominance of the reaction π+(np)→pp and by using the impulse approximation model; however a large fraction of them (∼40%) is due to the absorption on an α-cluster: π+(α)→ppd with very-low-energy transfer to the deuteron. Three-prong events have been interpreted as due to the process π+(α)→pppn and qualitative agreement between data and theory has been found. Some data on many-prong events are also reported.