Feasibility study of the eta-prime -> pi+pi-pi0 decay using WASA-at-COSY   apparatus
  One of the objectives of the vast physics programme of the recently comissioned WASA-at-COSY facility is the study of fundamental symmetries via the measurements of the eta and eta-prime mesons decays. Especially interesting are isospin violating hadronic precesses of these mesons into 3pi systems driven by the term of QCD Lagrangian which depends on the mass difference of the u and d quarks. When an eta or an eta-prime meson is created in the hadronic reaction signals from such decays may be significantly obscured by the prompt production of pi mesons. In this thesis we present the estimation of the upper limit of the background due to prompt pion production for the eta-prime ->3pi0 and eta-prime->pi+pi-pi decays. Using the data from proton-proton collisions measured by the COSY-11 group we have extracted differential cross sections for the multimeson production with the invariant mass corresponding to the mass of the eta-prime meson. Based on these results and on parametrizations of the total cross sections for the eta-prime meson as well as parametrization of the upper limit for the prompt pi+pi-pi0 production in the collisions of protons we discuss in details the feasibility of a measurement of the eta-prime meson decay into 3pi channels with the WASA-at-COSY facility. Based on the chiral unitary approach the value of the branching ratio BR(eta-prime->pi+pi-pi0) was recently predicted to be about 1%. We show that the WASA-at-COSY has a potential to verify this result empirically. 
Marcin J. Zielinski