Excitation function for He4(π+,pp)2H two-nucleon absorption across the Δ resonance

Angular distributions and total cross sections for the He-4(pi+, pp)H-2 reaction have been measured with small relative uncertainties at incident energies of T(pi+) = 64, 87, 114, 162, 217, 278, and 327 MeV. The results strongly support the quasideuteron absorption model for pion absorption on two nucleons, which is found to contribute only almost-equal-to 50% to the total absorption cross section near the DELTA resonance. All essential reaction channels of pion absorption near the DELTA resonance on heavier nuclei seem to be present in He-4, but not in He-3. Any nuclear-density-related increase of pion absorption in He-4 relative to H-2 is <50% and no binding energy effect is found.