Multiproton final states in positive pion absorption below theΔ(1232)resonance

Abstract

Inclusive cross sections for positive pion absorption leading to final states including two or more protons have been measured with a large solid angle detector for incident pion energies from 30 to 135 MeV for targets with $A=2--208.$ The mass dependences for the inclusive $({\ensuremath{\pi}}^{+},2p),$ $({\ensuremath{\pi}}^{+},3p),$ and total absorption cross sections for multiproton final states were found to be proportional to ${A}^{n}$ with $n\ensuremath{\approx}0.5.$ These cross sections also were observed to have an energy dependence at energies below 150 MeV reflective of the importance of the $\ensuremath{\Delta}(1232)$ resonance, similar to that observed for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The inclusive cross sections for $({\ensuremath{\pi}}^{+},4p)$ were found to be less than 10 mb for all targets at all energies. Estimates were also obtained for cross sections for pion absorption leading to $2p1n$ and $3p1n$ final states. Quasideuteron absorption contributions increase slowly with A, and the energy dependence of those contributions mirrors that for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The data obtained here for multiproton final states indicate that a significant fraction of absorption events, increasing with A, most likely arises from final states containing fewer than two protons.