Observation of eta ' -> omega e(+)e(-)
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Based on a sample of ?? mesons produced in the radiative decay J/????? in 1.31×109 J/? events collected with the BESIII detector, the decay ????e+e- is observed for the first time, with a statistical significance of 8?. The branching fraction is measured to be B(????e+e-)=(1.97±0.34(stat)±0.17(syst))×10-4, which is in agreement with theoretical predictions. The branching fraction of ????? is also measured to be (2.55±0.03(stat)±0.16(syst))×10-2, which is the most precise measurement to date, and the relative branching fraction B(????e+e-)B(?????) is determined to be (7.71±1.34(stat)±0.54(syst))×10-3. © 2015 American Physical Society.