Isospin effects in the exclusive dp \( \rightarrow\)3He\( \pi^{+}\)\( \pi^{-}\) reaction

The differential cross section for the exclusive \( dp\rightarrow {}^{3}{\rm He} \pi^+\pi^-\) reaction has been measured with high resolution and large statistics over a large fraction of the backward 3He hemisphere at the excess energy 265 MeV using the COSY-ANKE magnetic spectrometer. Though the well-known ABC enhancement is observed in the \( \pi^+\pi^-\) spectrum, the differences detected between the \( \pi^+{}^{3}{\rm He}\) and \( \pi^-{}^{3}{\rm He}\) invariant-mass distributions show that there must be some isospin-one \( \pi\) \( \pi\) production even at relatively low excess energies. The invariant-mass differences are modeled in terms of the sequential decay \( N^*(1440)\rightarrow\Delta(1232)\pi\rightarrow N\pi\pi\) .