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.

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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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Using 2.92 fb −1 of electron-positron annihilation data collected at √ s = 3.773 GeV with the BESIII detector, we obtain the first measurements of the absolute branching fractionL e + νe differential decay rate distribution, the product of the hadronic form factor and the magnitude of the CKM matrix element, f K + (0)|Vcs|, is determined 3 to be 0.728 ± 0.006(stat.) ± 0.011(sys.). Using |Vcs| from the SM constrained fit with the measured f K + (0)|Vcs|, f K + (0) = 0.748 ± 0.007(stat.) ± 0.012(sys.) is obtained, and utilizing the unquenched LQCD calculation for f K + (0), |Vcs| = 0.975 ± 0.008(stat.) ± 0.015(sys.) ± 0.025(LQCD).

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