Direct three-nucleon pion-absorption processes in 3He

A new reaction mechanism has been discovered in pion absorption on 3 He in which all three nucleons of the target are involved. From detailed measurements it has been shown that this type of reaction has a constant matrix element over the entire phase space of the 3N final state. This feature strongly supports a direct three-nucleon absorption process. Sequential processes like knock-out of one nucleon with subsequent absorption of the pion on the other two nucleons can be excluded. The fraction of the new reaction mechanism was found to be approximately 20% of the total pion absorption cross section in 3He. Possible relations of the new process with a three-body force are briefly mentioned.