Partial wave analysis of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>γ</mml:mi><mml:mi>η</mml:mi><mml:msup><mml:mrow><mml:mi>η</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>
M. Ablikim, М. Н. Ачасов, P. Adlarson, S. Ahmed, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, X. H. Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, V. Batozskaya, D. Becker, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, H. Cai, X. Z. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Çetin, J. F. Chang, W. L. Chang, G. Chelkov, C. Chen, G. Chen, H. S. Chen, M. L. Chen, S. J. Chen, T. Chen, X. R. Chen, X. T. Chen, Y. B. Chen, Z. J. Chen, W. S. Cheng, G. Cibinetto, F. Cossio, J. J. Cui, X. F. Cui, H. L. Dai, J. P. Dai, X. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, C. Dong, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, M. Fritsch, C. D. Fu, Y. Gao, Y. Gao, I. Garzia, P. Ge, C. Geng, E. Gersabeck, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco, M. H. Gu, Y. T. Gu, C. Y. Guan, A. Q. Guo, A. Q. Guo, L. B. Guo, R. P. Guo
Abstract
Based on a sample of $(10.09\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}{10}^{9}$ $J/\ensuremath{\psi}$ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\eta}{\ensuremath{\eta}}^{\ensuremath{'}}$ is performed. An isoscalar state with exotic quantum numbers ${J}^{PC}={1}^{\ensuremath{-}+}$, denoted as ${\ensuremath{\eta}}_{1}(1855)$, has been observed for the first time with statistical significance larger than $19\ensuremath{\sigma}$. Its mass and width are measured to be $(1855\ifmmode\pm\else\textpm\fi{}{9}_{\ensuremath{-}1}^{+6})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and $(188\ifmmode\pm\else\textpm\fi{}{18}_{\ensuremath{-}8}^{+3})\text{ }\text{ }\mathrm{MeV}$, respectively. The first uncertainties are statistical and the second are systematic. The product branching fraction $\mathcal{B}(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{1}(1855))\mathcal{B}({\ensuremath{\eta}}_{1}(1855)\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\eta}}^{\ensuremath{'}})$ is measured to be $(2.70\ifmmode\pm\else\textpm\fi{}{0.41}_{\ensuremath{-}0.35}^{+0.16})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. In addition, an upper limit on the ratio of branching fractions $\mathcal{B}({f}_{0}(1710)\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\eta}}^{\ensuremath{'}})/\mathcal{B}({f}_{0}(1710)\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi})$ is determined to be $1.61\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ at 90% confidence level, which lends support to the hypothesis that the ${f}_{0}(1710)$ has a large glueball component.