The first evidence is presented that the phase pattern of the planar-transverse optimal reaction amplitudes found previously for elastic-scattering strong-interaction reactions also holds for nonelastic reactions. The pattern is observed in the reaction $p+p\to d+\pi$ in the energy range between 300 and 800 MeV.

• Received 7 November 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.517