Measurement of the $pn \rightarrow pp\pi ^{0}\pi ^{-}$ reaction in search for the recently observed resonance structure in $d\pi ^{0}\pi ^{0}$ and $d\pi ^{+}\pi ^{-}$ systems.

Exclusive measurements of the quasifree $pn\rightarrow pp\pi ^{0}\pi ^{-}$ reaction have been performed by means of pd collisions at $T_{p}$= 1.2 GeV using the wide angle shower apparatus (WASA) detector setup at the cooler synchrotron COSY (Institut für Kernphysik, Jülich). Total and differential cross sections have been obtained covering the energy region $\sqrt{8}=\left ( 2.35-2.46 \right )$ GeV, which includes the region of the ABC effect and its associated resonance structure. No ABC effect, i.e., low-mass enhancement is found in the $\pi ^{0}\pi ^{-}$ -invariant mass spectrum, in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s wave. At the upper end of the covered energy region t-channel processes for Roper, $\Delta \left ( 1600 \right )$ and $\Delta \Delta$ excitations provide a reasonable description of the data, but at low energies the measured cross sections are much larger than predicted by such processes. Adding a resonance amplitude for the resonance at m=2.37 GeV with $\Gamma$ =70 MeV and $I\left ( J^{P} \right )=0\left ( 3^{+} \right )$ observed recently in $pn\rightarrow d\pi ^{0}\pi ^{0}$ and $pn\rightarrow d\pi ^{+}\pi ^{-}$ reactions leads to an agreement with the data also at low energies