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Using e + e − collision data corresponding to a total integrated luminosity of 12.9 fb −1 collected with the BESIII detector at the BEPCII collider, the exclusive Born cross sections and the effective form factors of the reaction e + e − → Ξ − Ξ+ are measured via the single baryon-tag method at 23 center-of-mass energies between 3.510 and 4.843 GeV. Evidence for the decay ψ(3770) → Ξ − Ξ+ is observed with a significance of 4.5σ by analyzing the measured cross sections together with earlier BESIII results. For the other charmonium(-like) states ψ(4040), ψ(4160), Y (4230), Y (4360), ψ(4415), and Y (4660), no significant signal of their decay to Ξ − Ξ+ is found. For these states, upper limits of the products of the branching fraction and the electronic partial width at the 90% confidence level are provided.
We report the observation of the X(3823) in the process e + e − → π + π − X(3823) → π + π − γχc1 with a statistical significance of 6.2σ, in data samples at center-of-mass energies √ s =4. 230, 4.260, 4.360, 4.420 and 4.600 GeV collected with the BESIII detector at the BEPCII electron positron collider. The measured mass of the X(3823) is (3821.7 ± 1.3 ± 0.7) MeV/c 2 , where the first error is statistical and the second systematic, and the width is less than 16 MeV at the 90% confidence level. The products of the Born cross sections for e + e − → π + π − X(3823) and the branching ratio B[X(3823) → γχc1,c2] are also measured. These measurements are in good agreement with the assignment of the X(3823) as the ψ(1 3 D2) charmonium state.PACS numbers: 13.20. Gd, 13.25.Gv, 14.40.Pq Since its discovery, charmonium -meson particles which contain a charm and an anti-charm quark -has been an excellent tool for probing Quantum Chromodynamics (QCD), the fundamental theory that describes the strong interactions between quarks and gluons, in the non-perturbative (low-energy, long-distance effects) regime, and remains of high interest both experimentally and theoretically. All of the charmonium states with masses that are below the open-charm threshold have been firmly established [1,2]; open-charm refers to mesons containing a charm quark (antiquark) and either an up or down antiquark (quark), such as D orD. However, the observation of the spectrum that are above the opencharm threshold remains unsettled. During the past decade, many new charmoniumlike states were discovered, such as the X(3872) [3], the Y (4260) [4,5] and the Z c (3900) [5][6][7]. These states provide strong evidence for the existence of exotic hadron states [8]. Although charged charmoniumlike states like the Z c (3900) provide convincing evidence for the existence of multi-quark states [9], it is more difficult to distinguish neutral candidate exotic states from conventional charmonium. Moreover, the study of transitions between charmonium(like) states, such as the Y (4260) → γX(3872) [10], is an important approach to probe their nature, and the connections between them. Thus, a more complete understanding of the charmonium(like) spectroscopy and their relations is necessary and timely. In this Letter, we report a search for the production of the ψ 2 state via the process e + e − → π + π − X, using 4.67 fb −1 data collected with the BESIII detector operating at the BEPCII storage ring [14] at center-of-mass (CM) energies that range from √ s = 4.19 to 4.60 GeV [15]. The ψ 2 candidates are reconstructed in their γχ c1 and γχ c2 decay modes, with χ c1,c2 → γJ/ψ and J/ψ → ℓ + ℓ − (ℓ = e or µ). A GEANT4-based [16] Monte Carlo (MC) simulation software package is used to optimize event selection criteria, determine the detection efficiency, and estimate the backgrounds. For the signal process, we generate 40,000 e + e − → π + π − X(3823) events at each CM energy indicated above, using an phase space model, with X(3823) → γχ c1,c2
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Received 5 July 2016, Revised 26 August 2016 * Supported by National Key Basic Research Program of China (2015CB856700), National Natural Science Foundation of China (NSFC) (10805053, 11125525, 11175188, 11235011, 11322544, 11335008, 11425524) Abstract: A measurement of the number of J/ψ events collected with the BESIII detector in 2009 and 2012 is performed using inclusive decays of the J/ψ. The number of J/ψ events taken in 2009 is recalculated to be (223.7 ± 1.4) × 10 6 , which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESIII software. The number of J/ψ events taken in 2012 is determined to be (1086.9 ± 6.0) × 10 6 . In total, the number of J/ψ events collected with the BESIII detector is measured to be (1310.6 ± 7.0) × 10 6 , where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
49A,49C Y. Ding( ) 27 C. Dong( ) 30 J. Dong( ) 1,a L. Y. Dong( ) 1 M. Y. Dong( ) 1,a S. X. Du( ) 53 P. F. Duan( ) 1 J. Z. Fan( ) 39 J. Fang( ) 1,a S. S. Fang( ) 1 X. Fang( ) 46,a Y. Fang( ) 1 L. Fava 49B,49C F. Feldbauer 22Guo( ) 28 Y. Guo( ) 1 Y. P. Guo( ) 22 Z. Haddadi 25 A. Hafner 22 S. Han( ) 51 X. Q. Hao( ) 15 F. A. Harris 42 K. L. He( ) 1 T. Held 4 Y. K. Heng( ) 1,a Z. L. Hou( ) 1 C. Hu( ) 28 H. M. Hu( ) 1 J. F. Hu( ) 49A,49C T. Hu( ) 1,a Y. Hu( ) 1 G. M. Huang( ) 6 G. S. Huang( ) 46,a J. S. Huang( ) 15 X. T. Huang( ) 33 Y. Huang( ) 29 T. Hussain 48 Q. Ji( ) 1 Q. P. Ji( ) 30 X. B. Ji( ) 1 X. L. Ji( ) 1,a L. W. Jiang( ) 51 X. S. Jiang( ) 1,a X. Y. Jiang( ) 30 J. B. Jiao( ) 33 Z. Jiao( ) 17 D. P. Jin( ) 1,a S. Jin( )
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