Study Of By J/ψâ†'nK_S~0(?)+c.c Decay At BESâ…¢

The research on the baryons structure has always been one of the most important field of the study on hadron physics and material microstructure. It is the main means that baryon spectrum and that of the various production and decay rate for the study of the internal structure and the interactions of baryons. The study of Charmonium particles J/ψwhich was found in 1974 have opened up a new areas for the study of spectrum. Charmounium decay shoud be widely recognized as the ideal place for the baryons physical study of N*,Λ*andΣ* baryons excited state and so on. After Beijing Electron Positron Collider and Beijing Spectronmeter Upgraded, about 225M J/ψdata was obtained in the summer of 2009, which is by far the largest J/ψdata sample in the world. Using of the data, through charmonium decays can improve the data quality of baryons excited states and further improve the baryon spectrum.Based on the 2.25 billion J/ψevents collected by the BESâ…¢detector at the BEPCâ…¡. This thesis carefully analyzed and studied baryon decay model J/ψâ†'nKS0Λ+c.c and the processes J/ψâ†'nKS0Λ,J/ψâ†'nKS0Λ,whose final state is npÏ€-Ï€+Ï€- and npÏ€+Ï€-Ï€+. The the data analysis process of these decay channels was discussed in great detail, including event selection,background analysis,signal fit and the measurement of branching ratios etc. Finally, their decay branching ratios were calculated exactly,the results are listed below Br (J/ψâ†'nKS0Λ±c.c=(5.92±0.11)×10-4 Br(J/ψâ†'nAS0Λ)=(2.92±0.06)×10-4 Br(J/ψâ†'nKS0Λ)=(3.03±0.06)×10-4For the results in BESII data, these measurements are more precise, statistical error is smaller. The results shows better. Using by the experimental data from that process, by studying the invariant mass spectrum of KS0Λ.There is an obvious enhancement in the structure near the threshold in the invariant mass spectrum of KS0Λ,whose results indicate that calculation data in BESâ…¢agree with experimental data at BESâ…¡.In addition, N(1710),N(1900) signals were also observed. For J/ψâ†'pK-Λin BESâ…¡, there is X(2075) signal found on the near-threshold of the invariant mass spectrum of pΛ.but, for the isospin decay process of J/ψâ†'nKS0Λat BESâ…¡, it observe there without apparent signal in the invariant mass spectrum of nΛ. The Research on BESâ…¢data as well as,we have observed that the structure of resonance is still not clear in the invariant mass spectrum of nΛ. However, we observedΛ(1520),Λ(1670),Λ(1690),Λ(1810) in the invariant mass spectrum of nKS0 very clearly and sharply. If further research on baryon excited states including quality,width,decay branching ratios,and spin-parity and so on,we need to detail them with partial wave analysis, we study on J/Ψâ†'nKsoA±c.c and its charge conjugation decay channels on BESâ…¢, which will mprove the data quality of baryons excited states and further improve the baryon spectrum. It is an great significant work for the studies of baryon excited states by using J/Ψdecays.