Open Access

Test of $C P$ Symmetry in the Neutral Decays of $Λ$ via $J / ψ \to Λ \bar{Λ}$

M. Ablikim ¹, M. N. Achasov ^4,c, P. Adlarson ⁸⁰, X. C. Ai ⁸⁵, R. Aliberti ³⁷, A. Amoroso ^79a,79c, Q. An^76,62,a, Y. Bai ⁶⁰, O. Bakina ³⁸ et al. (BESIII Collaboration)

O. Bakina ³⁸, Y. Ban ^48,h, H.-R. Bao ⁶⁸, V. Batozskaya ^1,46, K. Begzsuren³⁴, N. Berger ³⁷, M. Berlowski ⁴⁶, M. B. Bertani ^29a, D. Bettoni ^30a, F. Bianchi ^79a,79c, E. Bianco^79a,79c, A. Bortone ^79a,79c, I. Boyko ³⁸, R. A. Briere ⁵, A. Brueggemann ⁷³, H. Cai ⁸¹, M. H. Cai ^40,k,l, X. Cai ^1,62, A. Calcaterra ^29a, G. F. Cao ^1,68, N. Cao ^1,68, S. A. Cetin ^66a, X. Y. Chai ^48,h, J. F. Chang ^1,62, T. T. Chang ⁴⁵, G. R. Che ⁴⁵, Y. Z. Che ^1,62,68, C. H. Chen ⁹, Chao Chen ⁵⁸, G. Chen ¹, H. S. Chen ^1,68, H. Y. Chen ²⁰, M. L. Chen ^1,62,68, S. J. Chen ⁴⁴, S. M. Chen ⁶⁵, T. Chen ^1,68, X. R. Chen ^33,68, X. T. Chen ^1,68, X. Y. Chen ^11,g, Y. B. Chen ^1,62, Y. Q. Chen ¹⁵, Z. K. Chen ⁶³, J. C. Cheng ⁴⁷, L. N. Cheng ⁴⁵, S. K. Choi ¹⁰, X. Chu ^11,g, G. Cibinetto ^30a, F. Cossio ^79c, J. Cottee-Meldrum ⁶⁷, H. L. Dai ^1,62, J. P. Dai ⁸³, X. C. Dai ⁶⁵, A. Dbeyssi¹⁸, R. E. de Boer ³, D. Dedovich ³⁸, C. Q. Deng ⁷⁷, Z. Y. Deng ¹, A. Denig ³⁷, I. Denisenko ³⁸, M. Destefanis ^79a,79c, F. De Mori ^79a,79c, X. X. Ding ^48,h, Y. Ding ⁴², Y. X. Ding ³¹, J. Dong ^1,62, L. Y. Dong ^1,68, M. Y. Dong ^1,62,68, X. Dong ⁸¹, M. C. Du ¹, S. X. Du ⁸⁵, S. X. Du ^11,g, X. L. Du ⁸⁵, Y. Y. Duan ⁵⁸, Z. H. Duan ⁴⁴, P. Egorov ^38,b, G. F. Fan ⁴⁴, J. J. Fan ¹⁹, Y. H. Fan ⁴⁷, J. Fang ^1,62, J. Fang ⁶³, S. S. Fang ^1,68, W. X. Fang ¹, Y. Q. Fang ^1,62,a, L. Fava ^79b,79c, F. Feldbauer ³, G. Felici ^29a, C. Q. Feng ^76,62, J. H. Feng ¹⁵, L. Feng ^40,k,l, Q. X. Feng ^40,k,l, Y. T. Feng ^76,62, M. Fritsch ³, C. D. Fu ¹, J. L. Fu ⁶⁸, Y. W. Fu ^1,68, H. Gao ⁶⁸, Y. Gao ^76,62, Y. N. Gao ^48,h, Y. N. Gao ¹⁹, Y. Y. Gao ³¹, Z. Gao ⁴⁵, S. Garbolino ^79c, I. Garzia ^30a,30b, L. Ge ⁶⁰, P. T. Ge ¹⁹, Z. W. Ge ⁴⁴, C. Geng ⁶³, E. M. Gersabeck ⁷², A. Gilman ⁷⁴, K. Goetzen ¹², J. D. Gong ³⁶, L. Gong ⁴², W. X. Gong ^1,62, W. Gradl ³⁷, S. Gramigna ^30a,30b, M. Greco ^79a,79c, M. D. Gu ⁵³, M. H. Gu ^1,62, C. Y. Guan ^1,68, A. Q. Guo ³³, J. N. Guo ^11,g, L. B. Guo ⁴³, M. J. Guo ⁵², R. P. Guo ⁵¹, X. Guo ⁵², Y. P. Guo ^11,g, A. Guskov ^38,b, J. Gutierrez ²⁸, T. T. Han ¹, F. Hanisch ³, K. D. Hao ^76,62, X. Q. Hao ¹⁹, F. A. Harris ⁷⁰, C. Z. He ^48,h, K. L. He ^1,68, F. H. Heinsius ³, C. H. Heinz ³⁷, Y. K. Heng ^1,62,68, C. Herold ⁶⁴, P. C. Hong ³⁶, G. Y. Hou ^1,68, X. T. Hou ^1,68, Y. R. Hou ⁶⁸, Z. L. Hou ¹, H. M. Hu ^1,68, J. F. Hu ^59,j, Q. P. Hu ^76,62, S. L. Hu ^11,g, T. Hu ^1,62,68, Y. Hu ¹, Z. M. Hu ⁶³, G. S. Huang ^76,62, K. X. Huang ⁶³, L. Q. Huang ^33,68, P. Huang ⁴⁴, X. T. Huang ⁵², Y. P. Huang ¹, Y. S. Huang ⁶³, T. Hussain ⁷⁸, N. Hüsken ³⁷, N. in der Wiesche ⁷³, J. Jackson ²⁸, Q. Ji ¹, Q. P. Ji ¹⁹, W. Ji ^1,68, X. B. Ji ^1,68, X. L. Ji ^1,62, X. Q. Jia ⁵², Z. K. Jia ^76,62, D. Jiang ^1,68, H. B. Jiang ⁸¹, P. C. Jiang ^48,h, S. J. Jiang ⁹, X. S. Jiang ^1,62,68, Y. Jiang ⁶⁸, J. B. Jiao ⁵², J. K. Jiao ³⁶, Z. Jiao ²⁴, S. Jin ⁴⁴, Y. Jin ⁷¹, M. Q. Jing ^1,68, X. M. Jing ⁶⁸, T. Johansson ⁸⁰, S. Kabana ³⁵, N. Kalantar-Nayestanaki ⁶⁹, X. L. Kang ⁹, X. S. Kang ⁴², M. Kavatsyuk ⁶⁹, B. C. Ke ⁸⁵, V. Khachatryan ²⁸, A. Khoukaz ⁷³, O. B. Kolcu ^66a, B. Kopf ³, L. Kröger ⁷³, M. Kuessner ³, X. Kui ^1,68, N. Kumar ²⁷, A. Kupsc ^46,80, W. Kühn ³⁹, Q. Lan ⁷⁷, W. N. Lan ¹⁹, T. T. Lei ^76,62, M. Lellmann ³⁷, T. Lenz ³⁷, C. Li ⁴⁹, C. Li ⁴⁵, C. H. Li ⁴³, C. K. Li ²⁰, D. M. Li ⁸⁵, F. Li ^1,62, G. Li ¹, H. B. Li ^1,68, H. J. Li ¹⁹, H. L. Li ⁸⁵, H. N. Li ^59,j, Hui Li ⁴⁵, J. R. Li ⁶⁵, J. S. Li ⁶³, J. W. Li ⁵², K. Li ¹, K. L. Li ^40,k,l, L. J. Li ^1,68, Lei Li ⁵⁰, M. H. Li ⁴⁵, M. R. Li ^1,68, P. L. Li ⁶⁸, P. R. Li ^40,k,l, Q. M. Li ^1,68, Q. X. Li ⁵², R. Li ^17,33, S. X. Li ¹¹, Shanshan Li ^26,i, T. Li ⁵², T. Y. Li ⁴⁵, W. D. Li ^1,68, W. G. Li ^1,a, X. Li ^1,68, X. H. Li ^76,62, X. K. Li ^48,h, X. L. Li ⁵², X. Y. Li ^1,8, X. Z. Li ⁶³, Y. Li ¹⁹, Y. G. Li ^48,h, Y. P. Li ³⁶, Z. H. Li ⁴⁰, Z. J. Li ⁶³, Z. X. Li ⁴⁵, Z. Y. Li ⁸³, C. Liang ⁴⁴, H. Liang ^76,62, Y. F. Liang ⁵⁷, Y. T. Liang ^33,68, G. R. Liao ¹³, L. B. Liao ⁶³, M. H. Liao ⁶³, Y. P. Liao ^1,68, J. Libby ²⁷, A. Limphirat ⁶⁴, D. X. Lin ^33,68, L. Q. Lin ⁴¹, T. Lin ¹, B. J. Liu ¹, B. X. Liu ⁸¹, C. X. Liu ¹, F. Liu ¹, F. H. Liu ⁵⁶, Feng Liu ⁶, G. M. Liu ^59,j, H. Liu ^40,k,l, H. B. Liu ¹⁴, H. H. Liu ¹, H. M. Liu ^1,68, Huihui Liu ²¹, J. B. Liu ^76,62, J. J. Liu ²⁰, K. Liu ^40,k,l, K. Liu ⁷⁷, K. Y. Liu ⁴², Ke Liu ²², L. Liu ⁴⁰, Liang Liu ^76,q, L. C. Liu ⁴⁵, Lu Liu ⁴⁵, M. H. Liu ³⁶, P. L. Liu ¹, Q. Liu ⁶⁸, S. B. Liu ^76,62, W. M. Liu ^76,62, W. T. Liu ⁴¹, X. Liu ^40,k,l, X. K. Liu ^40,k,l, X. L. Liu ^11,g, X. Y. Liu ⁸¹, Y. Liu ^40,k,l, Y. Liu ⁸⁵, Y. B. Liu ⁴⁵, Z. A. Liu ^1,62,68, Z. D. Liu ⁹, Z. Q. Liu ⁵², Z. Y. Liu ⁴⁰, X. C. Lou ^1,62,68, H. J. Lu ²⁴, J. G. Lu ^1,62, X. L. Lu ¹⁵, Y. Lu ⁷, Y. H. Lu ^1,68, Y. P. Lu ^1,62, Z. H. Lu ^1,68, C. L. Luo ⁴³, J. R. Luo ⁶³, J. S. Luo ^1,68, M. X. Luo⁸⁴, T. Luo ^11,g, X. L. Luo ^1,62, Z. Y. Lv ²², X. R. Lyu ^68,o, Y. F. Lyu ⁴⁵, Y. H. Lyu ⁸⁵, F. C. Ma ⁴², H. L. Ma ¹, Heng Ma ^26,i, J. L. Ma ^1,68, L. L. Ma ⁵², L. R. Ma ⁷¹, Q. M. Ma ¹, R. Q. Ma ^1,68, R. Y. Ma ¹⁹, T. Ma ^76,62, X. T. Ma ^1,68, X. Y. Ma ^1,62, Y. M. Ma ³³, F. E. Maas ¹⁸, I. MacKay ⁷⁴, M. Maggiora ^79a,79c, S. Malde ⁷⁴, Q. A. Malik ⁷⁸, H. X. Mao ^40,k,l, Y. J. Mao ^48,h, Z. P. Mao ¹, S. Marcello ^79a,79c, A. Marshall ⁶⁷, F. M. Melendi ^30a,30b, Y. H. Meng ⁶⁸, Z. X. Meng ⁷¹, G. Mezzadri ^30a, H. Miao ^1,68, T. J. Min ⁴⁴, R. E. Mitchell ²⁸, X. H. Mo ^1,62,68, B. Moses ²⁸, N. Yu. Muchnoi ^4,c, J. Muskalla ³⁷, Y. Nefedov ³⁸, F. Nerling ^18,e, H. Neuwirth ⁷³, Z. Ning ^1,62, S. Nisar ³², Q. L. Niu ^40,k,l, W. D. Niu ^11,g, Y. Niu ⁵², C. Normand ⁶⁷, S. L. Olsen ^10,68, Q. Ouyang ^1,62,68, S. Pacetti ^29b,29c, X. Pan ⁵⁸, Y. Pan ⁶⁰, A. Pathak ¹⁰, Y. P. Pei ^76,62, M. Pelizaeus ³, H. P. Peng ^76,62, X. J. Peng ^40,k,l, Y. Y. Peng ^40,k,l, K. Peters ^12,e, K. Petridis ⁶⁷, J. L. Ping ⁴³, R. G. Ping ^1,68, S. Plura ³⁷, V. Prasad ³⁶, F. Z. Qi ¹, H. R. Qi ⁶⁵, M. Qi ⁴⁴, S. Qian ^1,62, W. B. Qian ⁶⁸, C. F. Qiao ⁶⁸, J. H. Qiao ¹⁹, J. J. Qin ⁷⁷, J. L. Qin ⁵⁸, L. Q. Qin ¹³, L. Y. Qin ^76,62, P. B. Qin ⁷⁷, X. P. Qin ⁴¹, X. S. Qin ⁵², Z. H. Qin ^1,62, J. F. Qiu ¹, Z. H. Qu ⁷⁷, J. Rademacker ⁶⁷, C. F. Redmer ³⁷, A. Rivetti ^79c, M. Rolo ^79c, G. Rong ^1,68, S. S. Rong ^1,68, F. Rosini ^29b,29c, Ch. Rosner ¹⁸, M. Q. Ruan ^1,62, N. Salone ^46,p, A. Sarantsev ^38,d, Y. Schelhaas ³⁷, K. Schoenning ⁸⁰, M. Scodeggio ^30a, W. Shan ²⁵, X. Y. Shan ^76,62, Z. J. Shang ^40,k,l, J. F. Shangguan ¹⁶, L. G. Shao ^1,68, M. Shao ^76,62, C. P. Shen ^11,g, H. F. Shen ^1,8, W. H. Shen ⁶⁸, X. Y. Shen ^1,68, B. A. Shi ⁶⁸, H. Shi ^76,62, J. L. Shi ^11,g, J. Y. Shi ¹, S. Y. Shi ⁷⁷, X. Shi ^1,62, H. L. Song ^76,62, J. J. Song ¹⁹, M. H. Song ⁴⁰, T. Z. Song ⁶³, W. M. Song ³⁶, Y. X. Song ^48,h,m, Zirong Song ^26,i, S. Sosio ^79a,79c, S. Spataro ^79a,79c, S. Stansilaus ⁷⁴, F. Stieler ³⁷, S. S Su ⁴², G. B. Sun ⁸¹, G. X. Sun ¹, H. Sun ⁶⁸, H. K. Sun ¹, J. F. Sun ¹⁹, K. Sun ⁶⁵, L. Sun ⁸¹, R. Sun ⁷⁶, S. S. Sun ^1,68, T. Sun ^54,f, W. Y. Sun ⁵³, Y. C. Sun ⁸¹, Y. H. Sun ³¹, Y. J. Sun ^76,62, Y. Z. Sun ¹, Z. Q. Sun ^1,68, Z. T. Sun ⁵², C. J. Tang⁵⁷, G. Y. Tang ¹, J. Tang ⁶³, J. J. Tang ^76,62, L. F. Tang ⁴¹, Y. A. Tang ⁸¹, L. Y. Tao ⁷⁷, M. Tat ⁷⁴, J. X. Teng ^76,62, J. Y. Tian ^76,62, W. H. Tian ⁶³, Y. Tian ³³, Z. F. Tian ⁸¹, I. Uman ^66b, B. Wang ¹, B. Wang ⁶³, Bo Wang ^76,62, C. Wang ^40,k,l, C. Wang ¹⁹, Cong Wang ²², D. Y. Wang ^48,h, H. J. Wang ^40,k,l, J. Wang ⁹, J. J. Wang ⁸¹, J. P. Wang ⁵², K. Wang ^1,62, L. L. Wang ¹, L. W. Wang ³⁶, M. Wang ⁵², M. Wang ^76,62, N. Y. Wang ⁶⁸, S. Wang ^40,k,l, Shun Wang ⁶¹, T. Wang ^11,g, T. J. Wang ⁴⁵, W. Wang ⁶³, W. P. Wang ³⁷, X. Wang ^48,h, X. F. Wang ^40,k,l, X. L. Wang ^11,g, X. N. Wang ^1,68, Xin Wang ^26,i, Y. Wang ¹, Y. D. Wang ⁴⁷, Y. F. Wang ^1,8,68, Y. H. Wang ^40,k,l, Y. J. Wang ^76,62, Y. L. Wang ¹⁹, Y. N. Wang ⁴⁷, Y. N. Wang ⁸¹, Yaqian Wang ¹⁷, Yi Wang ⁶⁵, Yuan Wang ^17,33, Z. Wang ^1,62, Z. Wang ⁴⁵, Z. L. Wang ², Z. Q. Wang ^11,g, Z. Y. Wang ^1,68, Ziyi Wang ⁶⁸, D. Wei ⁴⁵, D. H. Wei ¹³, H. R. Wei ⁴⁵, F. Weidner ⁷³, S. P. Wen ¹, U. Wiedner ³, G. Wilkinson ⁷⁴, M. Wolke⁸⁰, J. F. Wu ^1,8, L. H. Wu ¹, L. J. Wu ¹⁹, Lianjie Wu ¹⁹, S. G. Wu ^1,68, S. M. Wu ⁶⁸, X. Wu ^11,g, Y. J. Wu ³³, Z. Wu ^1,62, L. Xia ^76,62, B. H. Xiang ^1,68, D. Xiao ^40,k,l, G. Y. Xiao ⁴⁴, H. Xiao ⁷⁷, Y. L. Xiao ^11,g, Z. J. Xiao ⁴³, C. Xie ⁴⁴, K. J. Xie ^1,68, Y. Xie ⁵², Y. G. Xie ^1,62, Y. H. Xie ⁶, Z. P. Xie ^76,62, T. Y. Xing ^1,68, C. J. Xu ⁶³, G. F. Xu ¹, H. Y. Xu ², M. Xu ^76,62, Q. J. Xu ¹⁶, Q. N. Xu ³¹, T. D. Xu ⁷⁷, X. P. Xu ⁵⁸, Y. Xu ^11,g, Y. C. Xu ⁸², Z. S. Xu ⁶⁸, F. Yan ²³, L. Yan ^11,g, W. B. Yan ^76,62, W. C. Yan ⁸⁵, W. H. Yan ⁶, W. P. Yan ¹⁹, X. Q. Yan ^1,68, H. J. Yang ^54,f, H. L. Yang ³⁶, H. X. Yang ¹, J. H. Yang ⁴⁴, R. J. Yang ¹⁹, Y. Yang ^11,g, Y. H. Yang ⁴⁴, Y. Q. Yang ⁹, Y. Z. Yang ¹⁹, Z. P. Yao ⁵², M. Ye ^1,62, M. H. Ye ^8,a, Z. J. Ye ^59,j, Junhao Yin ⁴⁵, Z. Y. You ⁶³, B. X. Yu ^1,62,68, C. X. Yu ⁴⁵, G. Yu ¹², J. S. Yu ^26,i, L. W. Yu ^11,g, T. Yu ⁷⁷, X. D. Yu ^48,h, Y. C. Yu ⁸⁵, Y. C. Yu ⁴⁰, C. Z. Yuan ^1,68, H. Yuan ^1,68, J. Yuan ³⁶, J. Yuan ⁴⁷, L. Yuan ², M. K. Yuan ^11,g, S. H. Yuan ⁷⁷, Y. Yuan ^1,68, C. X. Yue ⁴¹, Ying Yue ¹⁹, A. A. Zafar ⁷⁸, F. R. Zeng ⁵², S. H. Zeng ⁶⁷, X. Zeng ^11,g, Y. J. Zeng ⁶³, Y. J. Zeng ^1,68, Y. C. Zhai ⁵², Y. H. Zhan ⁶³, S. N. Zhang ⁷⁴, B. L. Zhang ^1,68, B. X. Zhang ^1,a, D. H. Zhang ⁴⁵, G. Y. Zhang ¹⁹, G. Y. Zhang ^1,68, H. Zhang ^76,62, H. Zhang ⁸⁵, H. C. Zhang ^1,62,68, H. H. Zhang ⁶³, H. Q. Zhang ^1,62,68, H. R. Zhang ^76,62, H. Y. Zhang ^1,62, J. Zhang ⁶³, J. J. Zhang ⁵⁵, J. L. Zhang ²⁰, J. Q. Zhang ⁴³, J. S. Zhang ^11,g, J. W. Zhang ^1,62,68, J. X. Zhang ^40,k,l, J. Y. Zhang ¹, J. Z. Zhang ^1,68, Jianyu Zhang ⁶⁸, L. M. Zhang ⁶⁵, Lei Zhang ⁴⁴, N. Zhang ⁸⁵, P. Zhang ^1,8, Q. Zhang ¹⁹, Q. Y. Zhang ³⁶, R. Y. Zhang ^40,k,l, S. H. Zhang ^1,68, Shulei Zhang ^26,i, X. M. Zhang ¹, X. Y. Zhang ⁵², Y. Zhang ¹, Y. Zhang ⁷⁷, Y. T. Zhang ⁸⁵, Y. H. Zhang ^1,62, Y. P. Zhang ^76,62, Z. D. Zhang ¹, Z. H. Zhang ¹, Z. L. Zhang ³⁶, Z. L. Zhang ⁵⁸, Z. X. Zhang ¹⁹, Z. Y. Zhang ⁸¹, Z. Y. Zhang ⁴⁵, Z. Z. Zhang ⁴⁷, Zh. Zh. Zhang ¹⁹, G. Zhao ¹, J. Y. Zhao ^1,68, J. Z. Zhao ^1,62, L. Zhao ¹, L. Zhao ^76,62, M. G. Zhao ⁴⁵, S. J. Zhao ⁸⁵, Y. B. Zhao ^1,62, Y. L. Zhao ⁵⁸, Y. X. Zhao ^33,68, Z. G. Zhao ^76,62, A. Zhemchugov ^38,b, B. Zheng ⁷⁷, B. M. Zheng ³⁶, J. P. Zheng ^1,62, W. J. Zheng ^1,68, X. R. Zheng ¹⁹, Y. H. Zheng ^68,o, B. Zhong ⁴³, C. Zhong ¹⁹, H. Zhou ^37,52,n, J. Q. Zhou ³⁶, S. Zhou ⁶, X. Zhou ⁸¹, X. K. Zhou ⁶, X. R. Zhou ^76,62, X. Y. Zhou ⁴¹, Y. X. Zhou ⁸², Y. Z. Zhou ^11,g, A. N. Zhu ⁶⁸, J. Zhu ⁴⁵, K. Zhu ¹, K. J. Zhu ^1,62,68, K. S. Zhu ^11,g, L. Zhu ³⁶, L. X. Zhu ⁶⁸, S. H. Zhu ⁷⁵, T. J. Zhu ^11,g, W. D. Zhu ^11,g, W. J. Zhu ¹, W. Z. Zhu ¹⁹, Y. C. Zhu ^76,62, Z. A. Zhu ^1,68, X. Y. Zhuang ⁴⁵, J. H. Zou ¹, and J. Zu ^76,62 (BESIII Collaboration)

¹Institute of High Energy Physics, Beijing 100049, People’s Republic of China
²Beihang University, Beijing 100191, People’s Republic of China
³Bochum Ruhr-University, D-44780 Bochum, Germany
⁴Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia
⁵Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
⁶Central China Normal University, Wuhan 430079, People’s Republic of China
⁷Central South University, Changsha 410083, People’s Republic of China
⁸China Center of Advanced Science and Technology, Beijing 100190, People’s Republic of China
⁹China University of Geosciences, Wuhan 430074, People’s Republic of China
¹⁰Chung-Ang University, Seoul, 06974, Republic of Korea
¹¹Fudan University, Shanghai 200433, People’s Republic of China
¹²GSI Helmholtzcentre for Heavy Ion Research GmbH, D-64291 Darmstadt, Germany
¹³Guangxi Normal University, Guilin 541004, People’s Republic of China
¹⁴Guangxi University, Nanning 530004, People’s Republic of China
¹⁵Guangxi University of Science and Technology, Liuzhou 545006, People’s Republic of China
¹⁶Hangzhou Normal University, Hangzhou 310036, People’s Republic of China
¹⁷Hebei University, Baoding 071002, People’s Republic of China
¹⁸Helmholtz Institute Mainz, Staudinger Weg 18, D-55099 Mainz, Germany
¹⁹Henan Normal University, Xinxiang 453007, People’s Republic of China
²⁰Henan University, Kaifeng 475004, People’s Republic of China
²¹Henan University of Science and Technology, Luoyang 471003, People’s Republic of China
²²Henan University of Technology, Zhengzhou 450001, People’s Republic of China
²³Hengyang Normal University, Hengyang 421001, People’s Republic of China
²⁴Huangshan College, Huangshan 245000, People’s Republic of China
²⁵Hunan Normal University, Changsha 410081, People’s Republic of China
²⁶Hunan University, Changsha 410082, People’s Republic of China
²⁷Indian Institute of Technology Madras, Chennai 600036, India
²⁸Indiana University, Bloomington, Indiana 47405, USA
^29aINFN Laboratori Nazionali di Frascati, I-00044, Frascati, Italy
^29bINFN Sezione di Perugia, I-06100, Perugia, Italy
^29cUniversity of Perugia, I-06100, Perugia, Italy
^30aINFN Sezione di Ferrara, I-44122, Ferrara, Italy
^30bUniversity of Ferrara, I-44122, Ferrara, Italy
³¹Inner Mongolia University, Hohhot 010021, People’s Republic of China
³²Institute of Business Administration, University Road, Karachi, 75270 Pakistan
³³Institute of Modern Physics, Lanzhou 730000, People’s Republic of China
³⁴Institute of Physics and Technology, Mongolian Academy of Sciences, Peace Avenue 54B, Ulaanbaatar 13330, Mongolia
³⁵Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica 1000000, Chile
³⁶Jilin University, Changchun 130012, People’s Republic of China
³⁷Johannes Gutenberg University of Mainz, Johann-Joachim-Becher-Weg 45, D-55099 Mainz, Germany
³⁸Joint Institute for Nuclear Research, 141980 Dubna, Moscow region, Russia
³⁹Justus-Liebig-Universitaet Giessen, II. Physikalisches Institut, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany
⁴⁰Lanzhou University, Lanzhou 730000, People’s Republic of China
⁴¹Liaoning Normal University, Dalian 116029, People’s Republic of China
⁴²Liaoning University, Shenyang 110036, People’s Republic of China
⁴³Nanjing Normal University, Nanjing 210023, People’s Republic of China
⁴⁴Nanjing University, Nanjing 210093, People’s Republic of China
⁴⁵Nankai University, Tianjin 300071, People’s Republic of China
⁴⁶National Centre for Nuclear Research, Warsaw 02-093, Poland
⁴⁷North China Electric Power University, Beijing 102206, People’s Republic of China
⁴⁸Peking University, Beijing 100871, People’s Republic of China
⁴⁹Qufu Normal University, Qufu 273165, People’s Republic of China
⁵⁰Renmin University of China, Beijing 100872, People’s Republic of China
⁵¹Shandong Normal University, Jinan 250014, People’s Republic of China
⁵²Shandong University, Jinan 250100, People’s Republic of China
⁵³Shandong University of Technology, Zibo 255000, People’s Republic of China
⁵⁴Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
⁵⁵Shanxi Normal University, Linfen 041004, People’s Republic of China
⁵⁶Shanxi University, Taiyuan 030006, People’s Republic of China
⁵⁷Sichuan University, Chengdu 610064, People’s Republic of China
⁵⁸Soochow University, Suzhou 215006, People’s Republic of China
⁵⁹South China Normal University, Guangzhou 510006, People’s Republic of China
⁶⁰Southeast University, Nanjing 211100, People’s Republic of China
⁶¹Southwest University of Science and Technology, Mianyang 621010, People’s Republic of China
⁶²State Key Laboratory of Particle Detection and Electronics, Beijing 100049, Hefei 230026, People’s Republic of China
⁶³Sun Yat-Sen University, Guangzhou 510275, People’s Republic of China
⁶⁴Suranaree University of Technology, University Avenue 111, Nakhon Ratchasima 30000, Thailand
⁶⁵Tsinghua University, Beijing 100084, People’s Republic of China
^66aTurkish Accelerator Center Particle Factory Group, Istinye University, 34010, Istanbul, Turkey
^66bNear East University, Nicosia, North Cyprus, 99138, Mersin 10, Turkey
⁶⁷University of Bristol, H H Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom
⁶⁸University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁶⁹University of Groningen, NL-9747 AA Groningen, The Netherlands
⁷⁰University of Hawaii, Honolulu, Hawaii 96822, USA
⁷¹University of Jinan, Jinan 250022, People’s Republic of China
⁷²University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom
⁷³University of Muenster, Wilhelm-Klemm-Strasse 9, 48149 Muenster, Germany
⁷⁴University of Oxford, Keble Road, Oxford OX13RH, United Kingdom
⁷⁵University of Science and Technology Liaoning, Anshan 114051, People’s Republic of China
⁷⁶University of Science and Technology of China, Hefei 230026, People’s Republic of China
⁷⁷University of South China, Hengyang 421001, People’s Republic of China
⁷⁸University of the Punjab, Lahore-54590, Pakistan
^79aUniversity of Turin and INFN, I-10125, Turin, Italy
^79bUniversity of Eastern Piedmont, I-15121, Alessandria, Italy
^79cINFN, I-10125, Turin, Italy
⁸⁰Uppsala University, Box 516, SE-75120 Uppsala, Sweden
⁸¹Wuhan University, Wuhan 430072, People’s Republic of China
⁸²Yantai University, Yantai 264005, People’s Republic of China
⁸³Yunnan University, Kunming 650500, People’s Republic of China
⁸⁴Zhejiang University, Hangzhou 310027, People’s Republic of China
⁸⁵Zhengzhou University, Zhengzhou 450001, People’s Republic of China

^*Full author list given at the end of the Letter.
^aDeceased.
^bAlso at the Moscow Institute of Physics and Technology, Moscow 141700, Russia.
^cAlso at the Novosibirsk State University, Novosibirsk, 630090, Russia.
^dAlso at the NRC “Kurchatov Institute,” PNPI, 188300, Gatchina, Russia.
^eAlso at Goethe University Frankfurt, 60323 Frankfurt am Main, Germany.
^fAlso at Key Laboratory for Particle Physics, Astrophysics and Cosmology, Ministry of Education; Shanghai Key Laboratory for Particle Physics and Cosmology; Institute of Nuclear and Particle Physics, Shanghai 200240, People’s Republic of China.
^gAlso at Key Laboratory of Nuclear Physics and Ion-beam Application (MOE) and Institute of Modern Physics, Fudan University, Shanghai 200443, People’s Republic of China.
^hAlso at State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People’s Republic of China.
ⁱAlso at School of Physics and Electronics, Hunan University, Changsha 410082, China.
^jAlso at Guangdong Provincial Key Laboratory of Nuclear Science, Institute of Quantum Matter, South China Normal University, Guangzhou 510006, China.
^kAlso at MOE Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou 730000, People’s Republic of China.
^lAlso at Lanzhou Center for Theoretical Physics, Lanzhou University, Lanzhou 730000, People’s Republic of China.
^mAlso at Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
ⁿAlso at Helmholtz Institute Mainz, Staudinger Weg 18, D-55099 Mainz, Germany.
^oAlso at Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China.
^pPresent address: Silesian University in Katowice, Chorzow, 41-500, Poland.
^qPresent address: Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA.

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Phys. Rev. Lett. 136, 251802 – Published 23 June, 2026

DOI: https://doi.org/10.1103/5x9g-82jg

Abstract

Using $(10 087 \pm 44) \times 10^{6} J / ψ$ events collected with the BESIII detector, a full angular analysis is carried out on the process $J / ψ \to Λ \bar{Λ} \to n π^{0} \bar{p} π^{+} + c . c$ . The decay parameters $α_{0}$ for $Λ \to n π^{0}$ and ${\bar{α}}_{0}$ for $\bar{Λ} \to \bar{n} π^{0}$ are measured to be $0.668 \pm 0.007 \pm 0.002$ and $- 0.677 \pm 0.007 \pm 0.003$ , respectively, yielding the most precise test for $C P$ symmetry of neutral decays of $Λ$ , $A_{C P}^{0} = (α_{0} + {\bar{α}}_{0}) / (α_{0} - {\bar{α}}_{0})$ , to be $- 0.006 \pm 0.007 \pm 0.002$ . The ratios $α_{0} / α_{-}$ and ${\bar{α}}_{0} / α_{+}$ are determined to be $0.884 \pm 0.013 \pm 0.006$ and $0.885 \pm 0.013 \pm 0.004$ , where $α_{-}$ and $α_{+}$ are the decay parameters of $Λ \to p π^{-}$ and $\bar{Λ} \to \bar{p} π^{+}$ , respectively. The ratios, found to be smaller than unity by more than $5 σ$ , confirm the presence of the $Δ I = 3 / 2$ transition in the $Λ$ and $\bar{Λ}$ decays, which is expected to improve the theoretical calculations for isospin amplitudes, and $A_{C P}$ , in hyperon decays. In all results, the first and second uncertainties are statistical and systematic, respectively.

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Phys. Rev. Lett. 136, 251802– Published 23 June, 2026

Vol. 136, Iss. 25 — 26 June 2026

Received 29 October 2025
Revised 12 March 2026
Accepted 19 May 2026

DOI: https://doi.org/10.1103/5x9g-82jg

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Test of $C P$ Symmetry in the Neutral Decays of $Λ$ via $J / ψ \to Λ \bar{Λ}$

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Test of CP Symmetry in the Neutral Decays of Λ via J/ψ→ΛΛ¯

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Test of $C P$ Symmetry in the Neutral Decays of $Λ$ via $J / ψ \to Λ \bar{Λ}$