ETA AND ETA' PRODUCTION NEAR THRESHOLDS AND BACKWARD CHARGE-EXCHANGE DIFFERENTIAL CROSS SECTION IN PI--P REACTIONS

We have performed an experiment to study the reaction π-+p→η+n near threshold, preliminary to a forthcoming measurement of charge asymmetry in η-meson decay. The η was identified by the velocity of the associated neutron. We detected neutrons produced in the forward hemisphere in the center-of-mass system corresponding to the most energetic neutrons in the laboratory. Data were taken at π- momenta between 670 and 805 MeVc. The four neutron detectors made it possible to detect neutrons at angles of 0°to 21°from the incident pion beam. We present backward differential cross sections for both pion charge exchange and η production calculated from the data. We looked for η′ at pion momenta of 1.5 BeVc and observed none. We obtained σ(π-p→nη′)≤60 μb. © 1968 The American Physical Society.