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.

The first spin-transfer experiment performed for the pi (d) over right arrow-->(p) over right arrow p reaction is described. Three spin-transfer parameters for this pi-absorption process were determined, K-LS(a), K-SS(a), and K-NN(a) which correspond to the pi-production parameters, K-SL(a), K-SS(p) , and K-NN(P), of the time-reversed (p) over right arrow p-->(d) over right arrow pi process. Each observable was measured at a single angle for a number of energies spanning the 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 pp-->d 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.

Three-proton emission cross sections for the He-4(pi+, ppp)n reaction were measured at an incident pion kinetic energy of T-pi+ = 165 MeV over a wide angular range in a kinematically complete experiment. Angular correlations, missing momentum distributions, and energy spectra are compared with three- and four-body phase-space Monte Carlo calculations. The results provide strong evidence that most of the three-proton coincidences result from three-nucleon absorption. From phase-space integration the total three-nucleon absorption cross section is estimated to be sigma-3N = 4.8 +/- 1.0 mb. The cross section involving four nucleons is small and is estimated to be sigma-4N < 2 mb. On the scale of the total absorption cross section in He-4, multinucleon pion absorption seems to represent only a small fraction.

A broad goal of many few body physics experiments at intermediate energies is to identify shortcomings of our "conventional" descriptions based on nucleons, nucleon resonances and mesons. Fkom these shortcomings it is often hoped to glean some evidence for the contributions of quarks and gluons. In addition one establishes specific oals for particular reaction channels, which upon realization furthers the empiric3 understanding of that channel, and in some small way also contributes to the above broad goal. Studies of the set of reactions involving the n-NN system must take into account the fact that this system is composed of a coupled set of reactions and that what is learned from one channel improves our understanding of the other coupled channels.

The results of an experiment of pion-induced pion production on 16O at a laboratory energy of 280 MeV are reported. The four-fold-differential cross section, d4σdΩπ+dΩπ+dEπ+dEπ, was measured, and the missing mass, Mx, for the reaction 16Ofs(π+,π+π−) at laboratory angles of 50°, 80° and 115° for the π−, and from 22° to 128° for the π+ was deduced. The angular and energy distributions of the many-fold differential cross sections are compared with an A(π+,π+π−) model for the reaction. The observed cross sections are reproduced in magnitude and shape when the theoretical calculations consider a proper pion dispersion relation, \̃gw(q), inside the nuclear medium. The total cross section, deduced by integrating the four-fold differential cross sections, is compared with the available theoretical predictions for the 16O(π+, π+π−) reaction.

Three-proton emission cross sections for the4He(π+, ppp)n reaction were measured at Tπ+=165 MeV over a wide angular range in a kinematically complete experiment. The momentum distribution of the undetected neutron and angular correlations have been compared with three- and four-body phase space Monte Carlo calculations. The results indicate that most of the three-proton coincidences result from three nucleon absorption. The total three-nucleon absorption cross section is estimated to be σ3N=4.5±1.0 mb from phase-space integration. This cross section does not account for the discrepancy between total absorption cross sections and two-nucleon absorption cross sections.

The excitation function of the 15.11 MeV (1/sup +/,T = 1) state in /sup 12/C has been measured by using the (..pi..,..pi..\u0027..gamma..) angular correlation technique. By this method, the background can be suppressed substantially. The relative cross section ratio of the 15.11 MeV (1/sup +/,T = 1) and the 12.71 MeV (1/sup +/,T = 0) state as a function of the pion incident energy is found to show a resonancelike behavior in the region of the ..delta.. resonance, in agreement with previous measurements of Morris et al.

Angular distributions of the tensor analyzing powers T20 and τ21 have been measured for πd↘ elastic scattering, in a single scattering experiment employing a tensor polarized deuteron target. Measurements of T20 were obtained for pion bombarding energies of 134, 151, 180, 220, and 256 MeV. Measurements of τ21 were obtained for pion bombarding energies of 134, 180, and 220 MeV. The results are compared with three‐body calculations where effects relating to pion absorption are seen to play an important role.

Pion-\ensuremath{\gamma} angular correlations have been measured both in and out of the reaction plane for the reaction $^{12}\mathrm{C}$(\ensuremath{\pi},\ensuremath{\pi}'${)}^{12}$${\mathrm{C}}^{\mathrm{*}}$(${2}^{+}$, 4.44 MeV), $^{12}$${\mathrm{C}}^{\mathrm{*}}$${\ensuremath{\rightarrow}}^{12}$C(g.s.)+\ensuremath{\gamma}. Data are presented at a pion momentum transfer of q=0.47 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ for incident pion energies of 116, 140, 162, 180, and 226 MeV and at q=0.85 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ for energies of 116, 162, and 226 MeV. A detailed description of the experimental setup together with the applied test procedures and of the data analysis is given. The data are compared to predictions of the \ensuremath{\Delta}-hole model and its static limit.

Particle-γ angular correlation technique can be used to determine the efficiency of γ-detectors. This method is demonstrated for 4.44 MeV γ-rays from the reaction 12C(α, α′γ).