Study of the reaction π−p↑ → π−π+n on a polarized proton target at 17.78 GeV/ c. Experiment and amplitude analysis

Abstract

We present the results of an experimental study of the reaction of dipion production by a beam of negative pions with momentum 17.78 GeV/ c on polarized proton andliquid hydrogen targets. The experiment covers the region of dipion masses near the mass of the ϱ-meson and small transferred momenta | t| < 0.2 (GeV/ c) 2. The complete set of spin density matrix elements was reconstructed and model-independent and model-dependent amplitude analyses of the reaction were performed. The experiment allows us to exclude the ambiguity of the amplitude analysis existing at high energies. The results contain evidence in favour of the existence of a σ(750) 00 ++. The data also allows us to estimate the intercept of the a 1-meson Regge trajectory. The experiment was performed at the ITEP proton synchrotron, Moscow.