Study Of E~+e~-→π~+π~-η At BESⅢ

Using experimental data collected in the center-of-mass energy ranging of 2.0-2.95 GeV on Beijing Spectrometer(BESⅢ),the study on the process e+e+→π+π-η was carried out.The thesis consists of literature reading,event selection program construction,selection criteria optimization,background suppression,detection efficiency determination,cross section fitting,and systematic uncertainty study.There are summarized as follows.Firstly,reconstructing the events of the research process based on the BESⅢ offline software system(BOSS)and selecting the candidate events.Secondly,calculating detection efficiency by using MC simulation sample and mass weighted method,considering the cross section correction of initial radiation and vacuum polarization,the Born cross section spectrum of process e+e-→π+π-η was measured accurately in low energy region,and results are consistent with BABAR experiment within error and more accurate.Thirdly,studying the intermediate states involved in process e+e-→π+π-η.Measuring the cross section spectrum of the main intermediate resonance states,ρη and a2π.Based on ROOT data analysis framework,we fit the cross section spectrum and precisely measure the resonance parameters of meson p(2150).The fit results are M=2202.1±9.6 Mev/c2,Γ=43.2±21.5 MeV.These provide important experimental data for the study of excited p mesons and for the observed but not yet determined resonance states on BESⅢ.Besides,the θK has been re-evaluated via mass relations and latest experimental results,meanwhile,the M(K1B)also be obtained.Based on the singlet-octet mixing model and quark-flavor mixing model,theθh1 has been recalculated with a modified formula,by inputting M(K1B)instead of θK.The values are calculated to be |θK|=(42.6±2.2)°,M(K1B)=(1333.9±4.6)MeV/c2 and θh1=(29.5±2.0)°.Using these calculations as input,we predict that the branching fraction of J/ψ→η’(η)h1(1170)is about one order higher than that of J/Ψ→η’(η)h1(1415),which can be measured in future experiments to test the validity of these two models.