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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2013, vol. 87, p. -

Measurement of η<sup>′</sup>→π+<sup>π-</sup>e+ <sup>e-</sup> and η<sup>′</sup>→π+<sup>π-</sup>μ+ <sup>μ-</sup>

Ablikim M., Achasov M. N., Albayrak O., Ambrose D. J., An F. F., An Q., Bai J. Z., Baldini Ferroli R., Ban Y., Becker J., Bennett J. V., Bertani M., Bian J. M., Boger E., Bondarenko O., Boyko I., Briere R. A., Bytev V., Cai H., Cai X., Cakir O., Calcaterra A., Cao G. F., Cetin S. A., Chang J. F., Chelkov G., Chen G., Chen H. S., Chen J. C., Chen M. L., Chen S. J., Chen X., Chen Y. B., Cheng H. P., Chu Y. P., Cronin-Hennessy D., Dai H. L., Dai J. P., Dedovich D., Deng Z. Y., Denig A., Denysenko I., Destefanis M., Ding W. M., Ding Y., Dong L. Y., Dong M. Y., Du S. X., Fang J., Fang S. S., Fava L., Feng C. Q., Friedel P., Fu C. D., Fu J. L., Fuks O., Gao Y., Geng C., Goetzen K., Gong W. X., Gradl W., Greco M., Gu M. H., Gu Y. T., Guan Y. H., Guo A. Q., Guo L. B., Guo T., Guo Y. P., Han Y. L., Harris F. A., He K. L., He M., He Z. Y., Held T., Heng Y. K., Hou Z. L., Hu C., Hu H. M., Hu J. F., Hu T., Huang G. M., Huang G. S., Huang J. S., Huang L., Huang X. T., Huang Y., Huang Y. P., Hussain T., Ji C. S., Ji Q., Ji Q. P., Ji X. B., Ji X. L., Jiang L. L.

© 2013 American Physical Society. Based on a sample of 225.3 million J/ψ events accumulated with the BESIII detector at the BEPCII, the decays of η<sup>′</sup>→π <sup>+</sup>π<sup>-</sup>l<sup>+</sup>l<sup>-</sup> are studied via J/ψ→γη<sup>′</sup>. A clear η<sup>′</sup> signal is observed in the π<sup>+</sup>π<sup>-</sup>e<sup>+</sup>e <sup>-</sup> mass spectrum, and the branching fraction is measured to be B(η<sup>′</sup>→π<sup>+</sup>π<sup>-</sup>e <sup>+</sup>e<sup>-</sup>)=(2.11±0.12(stat)±0.14(syst)) ×10<sup>-</sup>3, which is in good agreement with theoretical predictions and the previous measurement, but is determined with much higher precision. No η<sup>′</sup> signal is found in the π<sup>+</sup>π <sup>-</sup>μ<sup>+</sup>μ<sup>-</sup> mass spectrum, and the upper limit is determined to be B(η<sup>′</sup>→π<sup>+</sup>π <sup>-</sup>μ<sup>+</sup>μ<sup>-</sup>)<2.9×10<sup>-</sup>5 at the 90% confidence level.