Study Of χ_cJ→pnÏ€^-（π⁰）+c.c. And J/ψ→pp（?） With The Besâ…¢ Detector At Bepcâ…¡

Since J/ψ was found in1974, lots of studies have been done in both experimental and theoretical aspects in charmonium physics. Till now, lots of topics in charmonium study are still hot. Charmonium hadron decays and the spectroscopy study are main physics goals of the charmonium study, which provide important information for investigating quantum chromodynamics (QCD), seaching for new decay modes and new resonances or particles. This thesis work is mainly to study the hadronic decays of XcJ and J J/ψ. Charmonium mesions are of cc quark pairs that are bound by the strong interaction. J/ψ and XcJ are the S-wave and P-wave charmonium state, respectively.The Beijing Electron-Position Collider (BEPCII) is running at the2.0～4.6GeV energy range. As the only facility running at tau-charm energy range now, the BEPCⅢ started to take data in2008with high stability and efficiency. Physics in this energy range is supposed to solve many unanswered questions in Standard Model, especially questions related to QCD. The upgraded Beijing Spectrometer (BESⅢ) is a huge facility applying to the high energy particle detection to fulfill the requirement of the high luminosity of BEPCII. Due to limited statistics because of indirect production in e+e-collisions, the decays of XcJ were not well studied yet. BESⅢ accumulated the world’s largest amount of ψ′data by now and XcJ are copiously produced in the ψ′adiative decays ψ′→γxcJ.Using a sample of106million ψ′decays collected by BEPCⅡ/BESⅢ, we study the process of XcJ decaying into pnπ-+c.c. and pnπ-π0+c.c. from the radiative decay of ψ′and measured the branching fractions precisely. The precision of the measured branching fractions of Xc0→pnπ-and xc2→pnπ-is significantly improved as compared with the existing PDG values. All the other branching fractions are measured for the first time. These measurements provide useful information for the understanding of the decay mechanism of the charmonium state XcJ.In addition, the invariant mass of the pπ-(c.c.) and nπ+(c.c.) from decay XcJ→pnπ-+c.c. show the broad resonances around1380MeV,1680MeV and2200MeV, which may be the states of N*and detailed study needs Partial Wave Analysis (PWA).Plenty of great achievements have been made on the hadronic spectroscopy study in J/ψ decays. In this thesis, the decay channel J/ψ→φpp has been studied via two decay modes φ→KS0KL0and φ→K+K-, using225.3million J/ψ sample accumulated at BESⅢ from June12,2009to July28,2009. Neither significant pp mass-threshold enhancement nor clear structure in the mass spectrum ofφp(p) is observed. The upper limit branching fraction of J/ψ→φX(pp)→φpp is set at90%confidence level and the branching fraction of J/ψ→φpp is measured with improved precision.