Production of the S01 diproton in the pp→ppπ0 reaction at 0.8 GeV

The pp→ppπ0 differential cross section has been measured with the ANKE spectrometer at COSY-Jülich for pion cms angles between 0° and 15.4° at a proton beam energy of 0.8 GeV. The selection of diproton pairs with an excitation energy Epp<3MeV ensures that the final pp system is dominantly in the spin-singlet S01 state. The kinematics are therefore very similar to those of pp→dπ+ but with different spin and isospin transitions. The cross sections are over two orders of magnitude smaller than those of pp→dπ+ and show a forward dip that is even stronger than that seen at lower energies. The results should provide a crucial extra test of pion production models in nucleon-nucleon collisions.