The reaction np $\rightarrow$ pp $\pi^-$ from threshold up to 570 MeV

Abstract

The reaction np\(\rightarrow\) pp\(\pi^-}\) has been studied in a kinematically complete measurement with a large acceptance time-of-flight spectrometer for incident neutron energies between threshold and 570 MeV. The proton-proton invariant mass distributions show a strong enhancement due to the pp(\(^1{\rm S}_0\)) final state interaction. A large anisotropy was found in the pion angular distributions in contrast to the reaction pp\(\rightarrow\)pp\(\pi^0\). At small energies, a large forward/backward asymmetry has been observed. From the measured integrated cross section \(\sigma({{\rm n}{\rm p} \rightarrow{\rm p}{\rm p} \pi^-})\), the isoscalar cross section \(\sigma_{01}\) has been extracted. Its energy dependence indicates that mainly partial waves with Sp final states contribute.