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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2014, vol. 113, 21, p. -

Observation of e+e- → π+π- hc and a Neutral Charmoniumlike Structure Zc(4020)0

Ablikim M., Achasov M. N., Ai X. C., Albayrak O., Albrecht M., Ambrose D. J., Amoroso A., An F. F., An Q., Bai J. Z., Baldini Ferroli R., Ban Y., Bennett D. W., Bennett J. V., Bertani M., Bettoni D., Bian A. J M, Bianchi F., Boger E., Bondarenko O., Boyko I., Briere R. A., Cai H., Cai X., Cakir O., Calcaterra A. A., Cao G. F., Cetin S. A., Chang B. J F, Chelkov G., Chen G., Chen H. S., Chen H. Y., Chen J. C., Chen M. L., Chen S. J., Chen X., Chen X. R., Chen Y. B., Cheng H. P., Chu X. K., Chu Y. P., Cibinetto G., Cronin-Hennessy D., Dai H. L., Dai J. P., Dedovich D., Deng Z. Y., Denig A., Denysenko I., Destefanis M., De Mori F., Ding Y., Dong C., Dong J., Dong L. Y., Dong M. Y., Du S. X., Duan P. F., Fan J. Z., Fang J., Fang S. S., Fang X., Fang Y., Fava L., Feldbauer F., Felici G., Feng C. Q., Fioravanti E., Fu A. C D, Gao Q., Gao Y., Garzia I., Goetzen A. 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., Guo Y. P., Haddadi Z., Hafner A., Han S., Han Y. L., Harris F. A.

© 2014 American Physical Society. Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of √s = 4.23, 4.26, and 4.36 GeV, we observe e+e- → π+π-hc for the first time. The Born cross sections are measured and found to be about half of those of e+e-→ π+π-hcwithin less than 2σ. In the π0hc mass spectrum, a structure at 4.02 GeV/c2 is found. It is most likely to be the neutral isospin partner of the Zc(4020)± observed in the process of e+e- → π+π-hc being found. A fit to the π0hc invariant mass spectrum, with the width of the Zc(4020)0 fixed to that of its charged isospin partner and possible interferences with non- Zc(4020)0 amplitudes neglected, gives a mass of (4023.9 ± 2.2 ± 3.8) MeV/c2 for the Zc(4020)0, where the first error is statistical and the second systematic.