Pion exchange effects in nuclear reactions at large momentum transfers

Abstract

The role of the inelastic pion channels of the nucleon-nucleon interaction at large momentum transfers is examined in view of recent experiments on nucleon transfer and pion production reactions. At energies below the pion production threshold the excitation functions of proton elastic back scattering from $^{2}\mathrm{H}$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ are characteristic of a simple nucleon exchange mechanism. The high energy region can be understood in terms of pion exchange contributions as expressed by triangle diagrams with the subprocesses $\mathrm{pp}\ensuremath{\rightarrow}^{2}\mathrm{H}\ensuremath{\pi}$, $p^{2}\mathrm{H}\ensuremath{\rightarrow}^{3}\mathrm{H}\ensuremath{\pi}$, and $p^{3}\mathrm{He}\ensuremath{\rightarrow}^{4}\mathrm{He}\ensuremath{\pi}$, respectively. Similarly, "hidden" pion exchange effects are suggested as an explanation for the excitation functions of $^{4}\mathrm{He}$($p$,$d$)$^{3}\mathrm{He}$ and $^{4}\mathrm{He}$($p$,$^{3}\mathrm{He}$)$^{2}\mathrm{H}$, invoking the proton backscattering reactions $p^{2}\mathrm{H}\ensuremath{\rightarrow}^{2}\mathrm{H}p$ and $p^{3}\mathrm{He}\ensuremath{\rightarrow}^{3}\mathrm{He}p$ as subprocesses.NUCLEAR REACTIONS ($p$,$p$) backscattering from $^{2}\mathrm{H}$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$, and $^{4}\mathrm{He}$($p$,$d$)$^{3}\mathrm{He}$ and $^{4}\mathrm{He}$($p$,$^{3}\mathrm{He}$)$^{2}\mathrm{H}$ for ${T}_{p}\ensuremath{\approx}100\ensuremath{-}700$ MeV; excitation functions of $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ (${\ensuremath{\theta}}_{0}$,$T$) analyzed in terms of nucleon exchange and pion exchange supported reaction mechanisms.