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Measurements of $J / ψ$ and $ψ (2 S)$ decays into $Λ \bar{Λ} π^{0}$ and $Λ \bar{Λ} η$

M. Ablikim¹, J. Z. Bai¹, Y. Ban¹¹, X. Cai¹, H. F. Chen¹⁶, H. S. Chen¹, H. X. Chen¹, J. C. Chen¹, Jin Chen¹ et al. (BES Collaboration)

Jin Chen¹, Y. B. Chen¹, Y. P. Chu¹, Y. S. Dai¹⁸, L. Y. Diao⁸, Z. Y. Deng¹, Q. F. Dong¹⁴, S. X. Du¹, J. Fang¹, S. S. Fang^1,*, C. D. Fu¹⁴, C. S. Gao¹, Y. N. Gao¹⁴, S. D. Gu¹, Y. T. Gu⁴, Y. N. Guo¹, Z. J. Guo^15,†, F. A. Harris¹⁵, K. L. He¹, M. He¹², Y. K. Heng¹, J. Hou¹⁰, H. M. Hu¹, J. H. Hu³, T. Hu¹, G. S. Huang^1,‡, X. T. Huang¹², X. B. Ji¹, X. S. Jiang¹, X. Y. Jiang⁵, J. B. Jiao¹², D. P. Jin¹, S. Jin¹, Y. F. Lai¹, G. Li^1,§, H. B. Li¹, J. Li¹, R. Y. Li¹, S. M. Li¹, W. D. Li¹, W. G. Li¹, X. L. Li¹, X. N. Li¹, X. Q. Li¹⁰, Y. F. Liang¹³, H. B. Liao¹, B. J. Liu¹, C. X. Liu¹, F. Liu⁶, Fang Liu¹, H. H. Liu¹, H. M. Liu¹, J. Liu^2,∥, J. B. Liu¹, J. P. Liu¹⁷, Jian Liu¹, Q. Liu¹⁵, R. G. Liu¹, Z. A. Liu¹, Y. C. Lou⁵, F. Lu¹, G. R. Lu⁵, J. G. Lu¹, C. L. Luo⁹, F. C. Ma⁸, H. L. Ma², L. L. Ma^1,¶, Q. M. Ma¹, Z. P. Mao¹, X. H. Mo¹, J. Nie¹, S. L. Olsen¹⁵, R. G. Ping¹, N. D. Qi¹, H. Qin¹, J. F. Qiu¹, Z. Y. Ren¹, G. Rong¹, X. D. Ruan⁴, L. Y. Shan¹, L. Shang¹, C. P. Shen¹⁵, D. L. Shen¹, X. Y. Shen¹, H. Y. Sheng¹, H. S. Sun¹, S. S. Sun¹, Y. Z. Sun¹, Z. J. Sun¹, X. Tang¹, G. L. Tong¹, G. S. Varner¹⁵, D. Y. Wang^1,**, L. Wang¹, L. L. Wang¹, L. S. Wang¹, M. Wang¹, P. Wang¹, P. L. Wang¹, W. F. Wang^1,††, Y. F. Wang¹, Z. Wang¹, Z. Y. Wang¹, Zheng Wang¹, C. L. Wei¹, D. H. Wei¹, Y. Weng¹, N. Wu¹, X. M. Xia¹, X. X. Xie¹, G. F. Xu¹, X. P. Xu⁶, Y. Xu¹⁰, M. L. Yan¹⁶, H. X. Yang¹, Y. X. Yang³, M. H. Ye², Y. X. Ye¹⁶, G. W. Yu¹, C. Z. Yuan¹, Y. Yuan¹, S. L. Zang¹, Y. Zeng⁷, B. X. Zhang¹, B. Y. Zhang¹, C. C. Zhang¹, D. H. Zhang¹, H. Q. Zhang¹, H. Y. Zhang¹, J. W. Zhang¹, J. Y. Zhang¹, S. H. Zhang¹, X. Y. Zhang¹², Yiyun Zhang¹³, Z. X. Zhang¹¹, Z. P. Zhang¹⁶, D. X. Zhao¹, J. W. Zhao¹, M. G. Zhao¹, P. P. Zhao¹, W. R. Zhao¹, Z. G. Zhao^1,‡‡, H. Q. Zheng¹¹, J. P. Zheng¹, Z. P. Zheng¹, L. Zhou¹, K. J. Zhu¹, Q. M. Zhu¹, Y. C. Zhu¹, Y. S. Zhu¹, Z. A. Zhu¹, B. A. Zhuang¹, X. A. Zhuang¹, and B. S. Zou¹ (BES Collaboration)

¹Institute of High Energy Physics, Beijing 100049, People’s Republic of China
²China Center for Advanced Science and Technology (CCAST), Beijing 100080, People’s Republic of China
³Guangxi Normal University, Guilin 541004, People’s Republic of China
⁴Guangxi University, Nanning 530004, People’s Republic of China
⁵Henan Normal University, Xinxiang 453002, People’s Republic of China
⁶Huazhong Normal University, Wuhan 430079, People’s Republic of China
⁷Hunan University, Changsha 410082, People’s Republic of China
⁸Liaoning University, Shenyang 110036, People’s Republic of China
⁹Nanjing Normal University, Nanjing 210097, People’s Republic of China
¹⁰Nankai University, Tianjin 300071, People’s Republic of China
¹¹Peking University, Beijing 100871, People’s Republic of China
¹²Shandong University, Jinan 250100, People’s Republic of China
¹³Sichuan University, Chengdu 610064, People’s Republic of China
¹⁴Tsinghua University, Beijing 100084, People’s Republic of China
¹⁵University of Hawaii, Honolulu, Hawaii 96822, USA
¹⁶University of Science and Technology of China, Hefei 230026, People’s Republic of China
¹⁷Wuhan University, Wuhan 430072, People’s Republic of China
¹⁸Zhejiang University, Hangzhou 310028, People’s Republic of China

^*Present address: DESY, D-22607, Hamburg, Germany.
^†Present address: Johns Hopkins University, Baltimore, MD 21218, USA.
^‡Present address: University of Oklahoma, Norman, OK 73019, USA.
^§Present address: Universite Paris XI, LAL-Bat. 208, BP34, 91898 Orsay Cedex, France.
^∥Present address: Max-Plank-Institut fuer Physik, Foehringer Ring 6, 80805 Munich, Germany.
^¶Present address: University of Toronto, Toronto M5S 1A7, Canada.
^**Present address: CERN, CH-1211 Geneva 23, Switzerland.
^††Present address: Laboratoire de l’Accélérateur Linéaire, Université, Paris-Sud 11, Bat. 208, BP34, 91898 Orsay Cedex, France.
^‡‡Present address: University of Michigan, Ann Arbor, MI 48109, USA.

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Phys. Rev. D 76, 092003 – Published 13 November, 2007

DOI: https://doi.org/10.1103/PhysRevD.76.092003

Abstract

Using $58 \times 10^{6}$ $J / ψ$ and $14 \times 10^{6}$ $ψ (2 S)$ events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays $J / ψ$ and $ψ (2 S) \to Λ \bar{Λ} π^{0}$ and $Λ \bar{Λ} η$ are measured. For the isospin violating decays, the upper limits are determined to be $B (J / ψ \to Λ \bar{Λ} π^{0}) < 6.4 \times 10^{- 5}$ and $B [ψ (2 S) \to Λ \bar{Λ} π^{0}] < 4.9 \times 10^{- 5}$ at the 90% confidence level. The isospin conserving process $J / ψ \to Λ \bar{Λ} η$ is observed for the first time, and its branching fraction is measured to be $B (J / ψ \to Λ \bar{Λ} η) = (2.62 \pm 0.60 \pm 0.44) \times 10^{- 4}$ , where the first error is statistical and the second one is systematic. No $Λ \bar{Λ} η$ signal is observed in $ψ (2 S)$ decays, and $B [ψ (2 S) \to Λ \bar{Λ} η] < 1.2 \times 10^{- 4}$ is set at the 90% confidence level. Branching fractions of $J / ψ$ decays into $Σ^{+} π^{-} \bar{Λ}$ and ${\bar{Σ}}^{-} π^{+} Λ$ are also reported, and the sum of these branching fractions is determined to be $B (J / ψ \to Σ^{+} π^{-} \bar{Λ} + c . c .) = (1.52 \pm 0.08 \pm 0.16) \times 10^{- 3}$ .