Exclusive ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm }$’p${)}^3$H spectra in the excitation energy range between 21.5 and 44 MeV in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ were measured at ${\mathit{T}}_{\mathrm{\pi }}$=180 MeV at several pion and proton angles. The cross section ratio ${\mathit{R}}_{\mathrm{\pi }\mathit{p}}$=σ(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$’p)/σ(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{\mathrm{-}}$’p) was found to be between 1 and 2 near 22 MeV which is in the region of the ${\mathit{J}}^{\mathrm{\pi }}$=$2^{\mathrm{-}}$, T=0 state. Between 25 and 40 MeV in the continuum, which comprises the giant dipole resonance and broad $2^{\mathrm{-}}$ and $2^{+}$ states, ${\mathit{R}}_{\mathrm{\pi }\mathit{p}}$ ranges from 0.22 to 45 in sharp contrast to the predicted values of ≊1 from a model assuming the entire yield is due to the sequential decay of a state of good isospin, and 6 to 9 from a distorted-wave impulse approximation calculation assuming quasifree proton knockout.

• Received 6 March 1990

DOI:https://doi.org/10.1103/PhysRevC.42.R807