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Study of by J/ψ→nK_S~0(?)+c.c Decay at BESⅢ

Author: ZhangWeiDong
Tutor: WeiDaiHui
School: Guangxi Normal University
Course: Theoretical Physics
Keywords: J / ψ decay Baryon excited states Monte Carlo Branching ratios BES Ⅲ
CLC: O572.33
Type: Master's thesis
Year: 2011
Downloads: 8
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Abstract


The baryon structure has been hadron physics, an important area of ??study of material microstructure, baryon spectrum, and a variety of produce and the decay rate is the primary means to study the internal structure of the baryon and interaction. Charmonium particles found in 1974 J / ψ as the baryon spectrum opened up a new field, the charmonium decay is generally accepted to study N * ∧ * Σ * baryons ideal place for the excited state. Beijing Electron Positron Collider and Beijing spectrometer after upgrading, acquired approximately 225M J / ψ data in the summer of 2009, which is currently the world's largest data sample of J / ψ. The use of the data by the charmonium decay can improve the baryon excitation states of data quality and further improve the baryon spectrum. Based on the BES Ⅲ get the 225 million J / ψ data on the final state npπ-π π-npπ π-π heavy sub-decay channel J / Ψ → nKsoA cc its charge total conjugated decay channels J / Ψ → nKsoA and J / Ψ → nKsoA carried out a detailed analysis of the study. Described in detail the process of data analysis of the decay channels, including event selection, background analysis, the signal fitting, branching ratio measurement, and finally accurately calculate the decay branching ratio, the results are as follows: Br (J /. Ψ → nKsoA ± cc): (5.92 ± 0.11) × 10-4 Br (J / .Ψ → nKsoA) = (2.92 ± 0.06) × 10-4 Br (J / .Ψ → nKsoA) = (3.03 ± 0.06) × 10-4 for the results of the measurement results than BES Ⅱ experimental data more precisely, the statistical error is small, with better results. Use obtained in the process of the experimental data, KS0 ∧ - the constant mass spectrum carried out the study, found K: OFF threshold value near observations to an obvious growth structure and the BES Ⅱ see the results, the addition is also observed to a N (1710) , N (1900) signal. Mass spectrum near threshold observed X (2075) signal for BES Ⅱ J / ψ → pK-∧ the pA unchanged. At BES Ⅱ the isospin decay process J / ψ → nKs0 ∧ nA invariant mass spectrum did not see a clear signal, the BES Ⅲ data in nA invariant mass spectrum, and found that this structure is still unclear. The invariant mass spectrum of the nKs0 we observed a very clear ∧ (1520), ∧ (1670), ∧ (1690), ∧ (1810). Detailed partial wave analysis of the need for further study of the excited states (including mass, width, decay branching ratio, as well as spin-parity) for baryon. BES Ⅲ J / ψ → nKs0 ∧ and charge conjugate decay channels can improve the baryon excited state of data quality and further improve the baryon spectrum. J / ψ decay process of baryon Road baryon excitation state of research is a rewarding job.

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CLC: > Mathematical sciences and chemical > Physics > Nuclear physics,high energy physics > High-energy physics > Particle types > Meson
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