Abstract
We study the e^{+}e^{-}→γωJ/ψ process using 11.6 fb^{-1} e^{+}e^{-} annihilation data taken at center-of-mass energies from sqrt[s]=4.008 GeV to 4.600GeV with the BESIII detector at the BEPCII storage ring. The X(3872) resonance is observed for the first time in the ωJ/ψ system with a significance of more than 5σ. The relative decay ratio of X(3872)→ωJ/ψ and π^{+}π^{-}J/ψ is measured to be R=1.6_{-0.3}^{+0.4}±0.2, where the first uncertainty is statistical and the second systematic (the same hereafter). The sqrt[s]-dependent cross section of e^{+}e^{-}→γX(3872) is also measured and investigated, and it can be described by a single Breit-Wigner resonance, referred to as the Y(4200), with a mass of 4200.6_{-13.3}^{+7.9}±3.0 MeV/c^{2} and a width of 115_{-26}^{+38}±12 MeV. In addition, to describe the ωJ/ψ mass distribution above 3.9 GeV/c^{2}, we need at least one additional Breit-Wigner resonance, labeled as X(3915), in the fit. The mass and width of the X(3915) are determined. The resonant parameters of the X(3915) agree with those of the Y(3940) in B→KωJ/ψ and of the X(3915) in γγ→ωJ/ψ observed by the Belle and BABAR experiments within errors.
Highlights
SidebandM(ωJ/ψ) (GeV/c 2)Data Fit X(3915) ωχ Bacc0kground Sideband background is well understood and can be reproduced by the MC simulation at BESIII [31]
Other possible backgrounds come from continuum events
They are estimated by analyzing the J
Summary
To improve the momentum and energy resolutions and to reduce backgrounds, a five-constraint (5C) kinematic fit is applied to an event with the hypothesis eþe− → γπþπ−π0lþl−, which constrains the sum of four momentum of the final-state particles to the initial colliding beams, and the mass of two photon combinations to the π0 world average mass [18]. Background events such as eþe− → πþπ−ψð3686Þ= π0π0ψð3686Þ → πþπ−π0π0J=ψ with one photon candidate missing would pass the previously described event selection To remove these backgrounds, we require jMrecoilðπþπ−Þ − m1⁄2ψð3686Þj > 8 MeV=c2 and jMðπþπ−J=pψÞffiffiffi−ffiffiffiffimffiffiffiffi1⁄2ffiψffiffiffiffiðffiffi3ffiffi6ffiffi8ffiffiffi6ffiffiÞffiffiffijffiffiffi> 7 MeV=c2, where Mrecoilðπþπ−Þ 1⁄4 ðPeþe− − Pπþπ− Þ2, and m1⁄2ψ ð3686Þ is the mass of the ψð3686Þ according to Ref.
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