The reaction np → pp π^- from threshold up to 570 MeV

¹ Fakultät für Physik der Universität Freiburg, 79104 Freiburg, Germany
² PSI, Paul-Scherrer-Institut, 5232 Villigen, Switzerland
³ Universita Karlova, MFF, V Holesovickach 2, 18000 Praha 8, Czech Republic
⁴ Joint Institute for Nuclear Research, LNP, 141980 Dubna, Moscow Region, Russia
⁵ DAPNIA/SPP, CEA/Saclay, 91191 Gif-sur-Yvette CEDEX, France

Received: 17 August 2001
Published online: 20 December 2001

Abstract

The reaction np → ppπ^- 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(¹S₀) final state interaction. A large anisotropy was found in the pion angular distributions in contrast to the reaction pp → ppπ⁰. At small energies, a large forward/backward asymmetry has been observed. From the measured integrated cross section σ(np → ppπ^-), the isoscalar cross section σ₀₁ has been extracted. Its energy dependence indicates that mainly partial waves with Sp final states contribute.