Feasibility study of measuring CP symmetry violation via eta->4pi decay   using WASA-at-COSY detector
  It is known that the Standard Model does not describe all phenomena related to subatomic particles. This thesis presents feasibility studies of the measurement of eta meson decay using WASA-at-COSY detector which tests predictions of the Standard Model. The aim of this thesis is to estimate the time of measurement for which the current branching ratio limit of eta -> 4pi0 decay can be improved. In order to estimate the time of measurement Monte Carlo simulations were performed. Kinematics of the pp -> ppeta -> pp4pi0 -> pp8gamma reactions were simulated using PLUTO program. Next, by means of the GEANT3 program the response of the WASA-at-COSY detector was simulated for each particle. Received signals were analysed in RootSorter software package based on ROOT. Studies of the reaction with many gamma quanta in the exit channel required the investigation of WASA-at-COSY calorimeter functioning. Tests of a cluster building algorithm with emphasis on merging and splitting of detected signals were done. The obtained result shows that only about 3% of eta -> 4p0 decays can be properly reconstructed. The identification of the eta -> 4pi0 -> 8gamma decay was based on the invariant mass method for both pi0 and eta mesons. As a result, the resolution of the invariant mass determination of the eta meson was established to sigma = 31 MeV/c2. The acceptance of the WASA-at-COSY detector for pp -> ppeta -> pp4pi0 -> pp8gamma reaction was determined to Aeta=(Neta detected) / (Neta produced) = 1.5%. The time of measurement for obtaining a statistical precision equal to the current branching ratio limit for Tbeam = 1.3 GeV is about 13 hours. It was also established that the lower the excess energy in the eta production is the shorter the time of the measurement needed. 
Tomasz Bednarski
hep-ex