Observation of Resonance Structures in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:msub><mml:mrow><mml:mi>ψ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>3823</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> and Mass Measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>ψ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>3823</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math>
M. Ablikim, М. Н. Ачасов, P. Adlarson, 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, A. Brueggemann, H. Cai, X. 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, H. L. Dai, J. P. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, 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, K. Fischer, M. Fritsch, C. D. Fu, He Gao, Yang Gao, Yang Gao, S. Garbolino, I. Garzia, P. Ge, Z. W. Ge, C. Geng, E. Gersabeck, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco, L. M. Gu, M. H. Gu, Y. T. Gu, C. Y. Guan, A. Q. Guo, L. B. Guo
Abstract
Using a data sample corresponding to an integrated luminosity of $11.3\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected at center-of-mass energies from 4.23 to 4.70 GeV with the BESIII detector, we measure the product of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\psi}}_{2}(3823)$ cross section and the branching fraction $\mathcal{B}[{\ensuremath{\psi}}_{2}(3823)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{c1}]$. For the first time, resonance structure is observed in the cross section line shape of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\psi}}_{2}(3823)$ with significances exceeding $5\ensuremath{\sigma}$. A fit to data with two coherent Breit-Wigner resonances modeling the $\sqrt{s}$-dependent cross section yields $M({R}_{1})=4406.9\ifmmode\pm\else\textpm\fi{}17.2\ifmmode\pm\else\textpm\fi{}4.5\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, $\mathrm{\ensuremath{\Gamma}}({R}_{1})=128.1\ifmmode\pm\else\textpm\fi{}37.2\ifmmode\pm\else\textpm\fi{}2.3\text{ }\text{ }\mathrm{MeV}$, and $M({R}_{2})=\phantom{\rule{0ex}{0ex}}4647.9\ifmmode\pm\else\textpm\fi{}8.6\ifmmode\pm\else\textpm\fi{}0.8\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, $\mathrm{\ensuremath{\Gamma}}({R}_{2})=33.1\ifmmode\pm\else\textpm\fi{}18.6\ifmmode\pm\else\textpm\fi{}4.1\text{ }\text{ }\mathrm{MeV}$. Though weakly disfavored by the data, a single resonance with $M(R)=4417.5\ifmmode\pm\else\textpm\fi{}26.2\ifmmode\pm\else\textpm\fi{}3.5\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, $\mathrm{\ensuremath{\Gamma}}(R)=245\ifmmode\pm\else\textpm\fi{}48\ifmmode\pm\else\textpm\fi{}13\text{ }\text{ }\mathrm{MeV}$ is also possible to interpret data. This observation deepens our understanding of the nature of the vector charmoniumlike states. The mass of the ${\ensuremath{\psi}}_{2}(3823)$ state is measured as $(3823.12\ifmmode\pm\else\textpm\fi{}0.43\ifmmode\pm\else\textpm\fi{}0.13)\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, which is the most precise measurement to date.