Reactions with Neutral Particles in the Final State at the Pion Channel of the Pnpi Synchrocyclotron

During several years, the Meson Physics Laboratory performs at the pion channel of the PNPI synchrocyclotron a wide program of investigation pion-nucleon scattering in the region of low-lying πN resonances. At the first stages of this program, precision measurements of the differential cross sections, polarization parameters P and spin rotation parameters A and R were made for πр elastic scattering at energies of incident pions in the range from 300 to 600 MeV (corresponding values of the incident pions momenta being from 417 to 725 MeV/c). In total, more than 400 new experimental points were obtained, which served – together with the results of experiments carried out at the Los-Alamos Meson Facility LAMRF – as a base of the new phase shift analysis PNPI-94. It became evidently in the course of performing this analysis that the mostly serious obstacle for determining phase shifts (and, consequently, partial amplitudes of πN scattering) with a higher precision is a lack of systematic data on πр charge exchange scattering and η-production process. That is why the investigation of reactions πр → πn and πр → ηn has become a logical continuation of earlier experiments on the study of πр elastic scattering. For performing this new series of experiments, the Neutral Meson Spectrometer was designed and created at PNPI.