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Measurement of η’→π+π-l+l-

Author: QinLiQing
Tutor: YangYongZuo; FangShuangShi
School: Guangxi Normal University
Course: Theoretical Physics
Keywords: light hadron pseudoscalar meson J/ψ η’ lepton rare decay
CLC: O572.243
Type: Master's thesis
Year: 2012
Downloads: 18
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Abstract


Quantum Chromodynamics(QCD)is the elementary theory of the strong interactions, and light hadron spectroscopy plays an prime role in the study of hadron physics and QCD. Four decades after the first observation of the η’ meson,its decays continue to provide a useful laboratory for probing strong interactions and new physics.The anomalous decay of η’ into π+π-l+l-(where l±stands either for e±or μ±)involves interesting fundamental features of the strong interactions. The possibility to study symmetries and symmetry-breaking patterns of low-energy QCD by means of η’ decays has induced considerable interest on both theoretical and experimental sides.Based on a sample of225.2million J/ψ events accumulated with the BES-Ⅲ detector at the BEPCⅡ,the rare decay of η’→π+π-l+l-was studied via J/ψ→γη’.Clear η’ signal was observed in the mass spectrum of π+π-e+e-:and branching ratio of η’→π+π-e+e-is determined to be BR(η’→π+π-e+e-)=(2.12±0.13(stat.)±0.19(syst.))×10-3,which is in good agreement with theoretical predications and previous measurement with a signif-icant improvement of the statistical error. No η’ signal is found in the mass spectrum of π+π-μ+μ-:and the upper limit of branching ratio,BR(η’→π+π-μ+μ-)<2.78×10-5. was given at90%confidence level.

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CLC: > Mathematical sciences and chemical > Physics > Nuclear physics,high energy physics > High-energy physics > Particle physics > Interaction > Strong interaction
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