Energy dependence of the He-4(pi+,pi-) total cross-section

The total cross section of the ${}^{4}\mathrm{He}({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}})$ reaction was measured for ${\ensuremath{\pi}}^{+}$ kinetic energies ranging from 70 to 130 MeV using the CHAOS spectrometer at TRIUMF and a liquid ${}^{4}\mathrm{He}$ target. Around ${T}_{\ensuremath{\pi}}=90\mathrm{MeV},$ total cross sections exceed conventional model predictions by a factor of 3, whereas at ${T}_{\ensuremath{\pi}}=70\mathrm{MeV}$ and for ${T}_{\ensuremath{\pi}}g130\mathrm{MeV}$ the data are consistent with these calculations. An attempt is made to understand this behavior by assuming the production of the hypothetical ${d}^{\ensuremath{'}}$ dibaryon.