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arXiv · 1610.02479

Amplitude analysis of the $\chi_{c1} \to \eta\pi^+\pi^-$ decays

M. Ablikim·M. N. Achasov·S. Ahmed·X. C. Ai·O. Albayrak·M. Albrecht·D. J. Ambrose·A. Amoroso·F. F. An·Q. An·J. Z. Bai·O. Bakina·R. Baldini Ferroli·Y. Ban·D. W. Bennett·J. V. Bennett·N. Berger·M. Bertani·D. Bettoni·J. M. Bian·F. Bianchi·E. Boger·I. Boyko·R. A. Briere·H. Cai·X. Cai·O. Cakir·A. Calcaterra·G. F. Cao·S. A. Cetin·J. Chai·J. F. Chang·G. Chelkov·G. Chen·H. S. Chen·J. C. Chen·M. L. Chen·S. Chen·S. J. Chen·X. Chen·X. R. Chen·Y. B. Chen·H. P. Cheng·X. K. Chu·G. Cibinetto·H. L. Dai·J. P. Dai·A. Dbeyssi·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·Z. L. Dou·S. X. Du·P. F. Duan·J. Z. Fan·J. Fang·S. S. Fang·X. Fang·Y. Fang·R. Farinelli·L. Fava·F. Feldbauer·G. Felici·C. Q. Feng·E. Fioravanti·M. Fritsch·C. D. Fu·Q. Gao·X. L. Gao·Y. Gao·Z. Gao·I. Garzia·K. Goetzen·L. Gong·W. X. Gong·W. Gradl·M. Greco·M. H. Gu·Y. T. Gu·Y. H. Guan·A. Q. Guo·L. B. Guo·R. P. Guo·Y. Guo·Y. P. Guo·Z. Haddadi·A. Hafner·S. Han·X. Q. Hao·F. A. Harris·K. L. He·F. H. Heinsius
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Abstract

Using $448.0 \times 10^6$~$\psi(3686)$ events collected with the BESIII detector, an amplitude analysis is performed for $\psi(3686)\to\gamma\chi_{c1}$, $\chi_{c1}\to\eta\pi^+\pi^-$ decays. The most dominant two-body structure observed is $a_0(980)^{\pm}\pi^{\mp}$; $a_0(980)^{\pm}\to\eta\pi^{\pm}$. The $a_0(980)$ line shape is modeled using a dispersion relation, and a significant non-zero $a_0(980)$ coupling to the $\eta^{\prime}\pi$ channel is measured. We observe $\chi_{c1}\to a_2(1700)\pi$ production for the first time, with a significance larger than 17$\sigma$. The production of mesons with exotic quantum numbers, $J^{PC}=1^{-+}$, is investigated, and upper limits for the branching fractions $\chi_{c1}\to \pi_1(1400)^{\pm}\pi^{\mp}$, $\chi_{c1}\to \pi_1(1600)^{\pm}\pi^{\mp}$, and $\chi_{c1}\to\pi_1(2015)^{\pm}\pi^{\mp}$, with subsequent $\pi_1(X)^{\pm} \to \eta\pi^{\pm}$ decay, are determined.

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M. Ablikim, M. N. Achasov, S. Ahmed, X. C. Ai, O. Albayrak, M. Albrecht, D. J. Ambrose, A. Amoroso, F. F. An, Q. An, J. Z. Bai, O. Bakina, R. Baldini Ferroli, Y. Ban, D. W. Bennett, J. V. Bennett, N. Berger, M. Bertani, D. Bettoni, J. M. Bian, F. Bianchi, E. Boger, I. Boyko, R. A. Briere, H. Cai, X. Cai, O. Cakir, A. Calcaterra, G. F. Cao, S. A. Cetin, J. Chai, J. F. Chang, G. Chelkov, G. Chen, H. S. Chen, J. C. Chen, M. L. Chen, S. Chen, S. J. Chen, X. Chen, X. R. Chen, Y. B. Chen, H. P. Cheng, X. K. Chu, G. Cibinetto, H. L. Dai, J. P. Dai, A. Dbeyssi, 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, Z. L. Dou, S. X. Du, P. F. Duan, J. Z. Fan, J. Fang, S. S. Fang, X. Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, E. Fioravanti, M. Fritsch, C. D. Fu, Q. Gao, X. L. Gao, Y. Gao, Z. Gao, I. Garzia, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco, M. H. Gu, Y. T. Gu, Y. H. Guan, A. Q. Guo, L. B. Guo, R. P. Guo, Y. Guo, Y. P. Guo, Z. Haddadi, A. Hafner, S. Han, X. Q. Hao, F. A. Harris, K. L. He, F. H. Heinsius. 2016-10-08. Amplitude analysis of the $\chi_{c1} \to \eta\pi^+\pi^-$ decays. https://doi.org/10.1103/physrevd.95.032002

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