Measurement of the helicity-dependent total cross-section for the $ \gamma$n $ \rightarrow$ p$ \pi^{-}_{}$$ \pi^{0}_{}$ reaction

The helicity dependence of the total cross-section for the \( \gamma\) n \( \rightarrow\) p \( \pi^{-}_{}\) \( \pi^{0}_{}\) reaction has been measured for the first time at incident photon energies from 450 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Both the measured unpolarized and the helicity-dependent observables are not well described by the existing theoretical models.