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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2012, vol. 109, p. -

First observation of the M1 transition ψ(3686) →γη c(2S)

Ablikim M., Achasov M. N., Ambrose D. J., An F. F., An Q., An Z. H., Bai J. Z., Ban Y., Becker J., Berger N., Bertani M., Bian J. M., Boger E., Bondarenko O., Boyko I., Briere R. A., Bytev V., Cai X., Calcaterra A., Cao G. F., Chang J. F., Chelkov G., Chen G., Chen H. S., Chen J. C., Chen M. L., Chen S. J., Chen Y., 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., Feldbauer F., Feng C. Q., Ferroli R. B., Fu C. D., Fu J. L., 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 Y. P., Han Y. L., Hao X. Q., Harris F. A., He K. L., He M., He Z. Y., Held T., Heng Y. K., Hou Z. L., Hu H. M., Hu J. F., Hu T., Huang B., Huang G. M., Huang J. S., Huang X. T., Huang Y. P., Hussain T., Ji C. S., Ji Q., Ji X. B., Ji X. L., Jia L. K., Jiang L. L., Jiang X. S., Jiao J. B., Jiao Z., Jin D. P., Jin S., Jing F. F., Kalantar-Nayestanaki N., Kavatsyuk M., Kuehn W.

Using a sample of 106×106 ψ(3686) events collected with the BESIII detector at the BEPCII storage ring, we have made the first measurement of the M1 transition between the radially excited charmonium S-wave spin-triplet and the radially excited S-wave spin-singlet states: ψ(3686) →γη c(2S). Analyses of the processes ψ(3686)→γη c(2S) with η c(2S) →KS0K ±π and K +K -π0 give an η c(2S) signal with a statistical significance of greater than 10 standard deviations under a wide range of assumptions about the signal and background properties. The data are used to obtain measurements of the η c(2S) mass (M(η c(2S))=3637.6±2.9 stat±1.6 systMeV/c2), width (Γ(η c(2S))=16.9±6.4 stat±4.8 systMeV), and the product branching-fraction (B(ψ(3686) →γη c(2S))×B(η c(2S) →KK̄π)=(1.30±0.20 stat±0.30 syst)×10 -5). Combining our result with a BABAR measurement of B(η c(2S)→KK̄π), we find the branching fraction of the M1 transition to be B(ψ(3686) →γη c(2S))=(6.8±1.1 stat±4. 5 syst)×10 -4. © 2012 American Physical Society.