Spin-transfer measurements of the π d → → p → p reaction at energies spanning the Δ resonance

The first spin-transfer experiment performed for the $\ensuremath{\pi}d\ensuremath{\rightarrow}\ensuremath{\rightarrow}p\ensuremath{\rightarrow}p$ reaction is described. Three spin-transfer parameters for this $\ensuremath{\pi}$-absorption process were determined, ${K}_{\mathrm{LS}}^{a}$, ${K}_{\mathrm{SS}}^{a}$, and ${K}_{\mathrm{NN}}^{a}$, which correspond to the \ensuremath{\pi}-production parameters, ${K}_{\mathrm{SL}}^{p}$, ${K}_{\mathrm{SS}}^{p}$, and ${K}_{\mathrm{NN}}^{p}$, of the time-reversed $p\ensuremath{\rightarrow}p\ensuremath{\rightarrow}d\ensuremath{\rightarrow}\ensuremath{\pi}$ process. Each observable was measured at a single angle for a number of energies spanning the $\ensuremath{\Delta}$ resonance of this system. The results are compared with the predictions of published partial wave amplitude fits which are primarily based on existing data for the time-reversed $\mathrm{pp}\ensuremath{\rightarrow}d\ensuremath{\pi}$ reaction, and also with the predictions of two current theories. The failure of these theories to describe the fundamental features of the data clearly demonstrates the need for further theoretical work in this area.