arXiv · 1612.07398
Observation of the helicity-selection-rule suppressed decay of the $\chi_{c2}$ charmonium state
Abstract
The decays of $\chi_{c2}\to K^{+}K^{-}\pi^{0}$, $K_{S} K^{\pm}\pi^{\mp}$ and $\pi^{+}\pi^{-}\pi^{0}$ are studied with the $\psi(3686)$ data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of $\chi_{c2}\to K^{\ast}\overline{K}$, $\chi_{c2}\to a_{2}^{\pm}(1320)\pi^{\mp}/a_{2}^{0}(1320)\pi^{0}$ and $\chi_{c2}\to \rho(770)^{\pm}\pi^{\mp}$ are measured. Here $K^{\ast}\overline{K}$ denotes both $K^{\ast\pm}K^{\mp}$ and $K^{\ast 0}\overline{K}{}^{0}+c.c.$, and $K^{\ast}$ denotes the resonances $K^{\ast}(892)$, $K^{\ast}_{2}(1430)$ and $K^{\ast}_{3}(1780)$. The observations indicate a strong violation of the helicity selection rule in $\chi_{c2}$ decays into vector and pseudoscalar meson pairs. The measured branching fractions of $\chi_{c2}\to K^{\ast}(892)\overline{K}$ are more than 10 times larger than the upper limit of $\chi_{c2}\to \rho(770)^{\pm}\pi^{\mp}$, which is so far the first direct observation of a significant $U$-spin symmetry breaking effect in charmonium decays.
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BESIII Collaboration, 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, 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. 2016-12-22. Observation of the helicity-selection-rule suppressed decay of the $\chi_{c2}$ charmonium state. https://doi.org/10.1103/physrevd.96.111102
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