Spin observables for thepd↔π+treaction around theΔresonance

Abstract

The proton analyzing power ${A}_{y0}$ and the deuteron tensor analyzing power ${T}_{20}$ are evaluated for the $\mathrm{pd}\ensuremath{\leftrightarrow}{\ensuremath{\pi}}^{+}t$ process, in the energy region around and above the $\ensuremath{\Delta}$ resonance. These calculations extend a previous analysis of the excitation function and differential cross section, based on a model embodying one- and two-body $p$-wave absorption mechanisms and isobar excitation. The three-nucleon bound state and the $\mathrm{pd}$ scattering state are evaluated through Faddeev techniques for both the Bonn and Paris potentials. The spin variables exhibit a greater sensitivity to the number of included three-nucleon partial waves than the cross sections, while the role played by the initial- or final-state interactions appears to be small. The results for the tensor analyzing power at backward angles show a non-negligible dependence on the potentials employed, consistently with what has been previously found for the cross sections. The calculation of spin observables gives a clear indication that other reaction mechanisms (presumably $s$-wave two-body absorption) have to be included in the model, in order to reproduce the experimental data below the $\ensuremath{\Delta}$ resonance, in analogy with the simpler $\mathrm{pp}\ensuremath{\leftrightarrow}\ensuremath{\pi}d$ process.