Preprint

Measurement of Branching Fraction and Transition Magnetic Moment of the Hyperon Dalitz Decay $\Sigma^0 \rightarrow \Lambda e^+e^-$

Besiii Collaboration M. Ablikim M. N. Achasov P. Adlarson X. Ai R. Aliberti A. Amoroso Q. An Y. Bai O. Bakina Y. Ban H.-R. Bao V. Batozskaya K. Begzsuren N. Berger M. Berlowski M. Bertani D. Bettoni F. Bianchi E. Bianco A. Bortone I. Boyko R. Briere A. Brueggemann H. Cai M.-H. Cai X. Cai A. Calcaterra Gui Cao N. Cao S. Cetin X.-Y. Chai J. Chang T. Chang G.-R. Che Y.-Z. Che C.-H. Chen Chao Chen G. Chen H.-S. Chen H.-Y. Chen M.-L. Chen S.-J. Chen S.-M. Chen T. Chen X.-R. Chen X.-T. Chen X.-Y. Chen Y.-B. Chen Y.-Q. Chen Z.-K. Chen J.-C. Cheng L.-N. Cheng S. Choi X. Chu G. Cibinetto F. Cossio J. Cottee-Meldrum H.-L. Dai J.-P. Dai X.-C. Dai A. Dbeyssi R. E. de Boer D. Dedovich Chi Deng Z.-Y. Deng A. Denig I. Denisenko M. Destefanis F. De Mori X.-X. Ding Y. Ding Y.-X. Ding J. Dong L.-Y. Dong Ming-Yi-Dong M. Y. Dong X. Dong M.-C. Du Shao-Xu Du X.-L. Du Y.-Y. Duan Z. Duan P. Egorov Gao Fan J.-J. Fan Y.-H. Fan J. Fang S.-S. Fang W.-X. Fang Y.-Q. Fang L. Fava F. Feldbauer G. Felici C. Feng J.-H. Feng L. Feng Q. Feng Y.-T. Feng M. Fritsch C.-D. Fu J.-L. Fu Y.-W. Fu H. Gao Y. Gao Y.-N. Gao Y.-Y. Gao Z. Gao S. Garbolino I. Garzia L. Ge P.-T. Ge Z.-W. Ge C. Geng E. Gersabeck A. Gilman K. Goetzen J. Gong L. Gong W. Gong W. Gradl S. Gramigna M. Greco M. Gu M.-H. Gu C. Guan A.-Q. Guo J.-N. Guo L.-B. Guo M.-J. Guo R. Guo X. Guo Y.-P. Guo A. Guskov J. Gutierrez T. Han F. Hanisch K.-D. Hao Xuan Hao F. Harris C.-Z. He K.-L. He F. H. Heinsius C. H. Heinz Y. Heng C. Herold P. Hong G.-Y. Hou Xia Hou Y.-R. Hou Zhen-Dong Hou H.-M. Hu J.-F. Hu Q.-P. Hu S.-L. Hu T. Hu Y. Hu Z.-M. Hu G.-S. Huang K.-X. Huang L.-Q. Huang P. Huang X.-T. Huang Y.-P. Huang Y.-S. Huang T. Hussain N. Hüsken N. D. der Wiesche J. Jackson Q. Ji Qiao Ji W. Ji X.-B. Ji X.-L. Ji X.-Q. Jia Z. Jia D. Jiang H.-B. Jiang P.-C. Jiang S.-J. Jiang X.-S. Jiang Y. Jiang J.-B. Jiao J.-K. Jiao Z. Jiao S. Jin Y. Jin M.-Q. Jing Xu Jing T. Johansson S. Kabana N. Kalantar-Nayestanaki X. Kang X. Kang M. Kavatsyuk B. Ke V. Khachatryan A. Khoukaz O. B. Kolcu B. Kopf L. Kröger M. Kuessner X. Kui N. Kumar A. Kupsc W. Kühn Q. Lan W.-N. Lan T. Lei M. Lellmann T. Lenz C. Li C.-H. Li C.-K. Li D.-M. Li F. Li G. Li H.-B. Li H.-J. Li H.-L. Li H.-N. Li Hui Li J.-R. Li J.-S. Li J.-W. Li K. Li K.-L. Li L.-J. Li Lei Li M.-H. Li M.-R. Li P.-L. Li P.-R. Li Q.-M. Li Q.-X. Li R. Li S.-X. Li Shan-Shan Li T. Li T.-Y. Li W.-D. Li W.-G. Li X. Li X.-H. Li X.-K. Li X.-L. Li X.-Y. Li X.-Z. Li Y. Li Y.-G. Li Y.-P. Li Z.-H. Li Z.-J. Li Z.-X. Li Z.-Y. Li C. Liang H. Liang Y.-F. Liang Y.-T. Liang Guo-Ya Liao Li-Dan Liao M. Liao Y.-P. Liao J. Libby A. Limphirat D. Lin L. Q. Lin T. Lin B.-J. Liu B.-X. Liu C.-X. Liu F. Liu F.-H. Liu Feng Liu G.-M. Liu H. Liu H.-B. Liu H.-H. Liu H.-M. Liu Hui-Hui Liu J.-B. Liu J.-J. Liu K. Liu K.-Y. Liu Ke Liu L. Liu L.-C. Liu Lu Liu M.-H. Liu Li-Yu Daisy Liu Q. Liu S.-B. Liu W.-M. Liu W.-T. Liu X. Liu X.-K. Liu X.-L. Liu X.-Y. Liu Y. Liu Y.-B. Liu Z.-A. Liu Z.-D. Liu Z.-Q. Liu Z.-Y. Liu X. Lou H.-J. Lu J.-G. Lu X.-L. Lu Y. Lu Y.-H. Lu Y.-P. Lu Z.-H. Lu C.-L. Luo J.-R. Luo J.-S. Luo M.-X. Luo T. Luo X.-L. Luo Z.-Y. Lv X. Lyu Y. Lyu Y. Lyu F.-C. Ma H.-L. Ma Heng Ma J.-L. Ma L.-L. Ma L.-R. Ma Q.-M. Ma R.-Q. Ma R. Ma T. Ma X.-T. Ma X.-Y. Ma Y.-M. Ma F. Maas I. Mackay M. Maggiora S. Malde Q. A. Malik Hua-Xing Mao Y.-J. Mao Z.-P. Mao S. Marcello A. Marshall F. M. Melendi Y.-H. Meng Zhen Meng G. Mezzadri H. Miao Tai-Shan Min R. Mitchell X.-H. Mo B. Moses N. Muchnoi J. Muskalla Y. Nefedov F. Nerling H. Neuwirth Z. Ning S. Nisar Q. Niu W.-D. Niu Y. Niu C. Normand S. L. Olsen Q. Ouyang S. Pacetti X. Pan Y. Pan A. Pathak Y.-P. Pei M. Pelizaeus H.-P. Peng X.-J. Peng Y.-Y. Peng K. Peters K. Petridis J.-L. Ping R. Ping S. Plura V. Prasad Fang-Zheng Qi H. Qi M. Qi S. Qian W.-B. Qian Chloe Qiao J.-H. Qiao J.-J. Qin J.-L. Qin Lei Qin Lang Qin P.-B. Qin X. Qin Xuan Qin Z. Qin J.-F. Qiu Z. Qu J. Rademacker C. F. Redmer A. Rivetti M. Rolo G. Rong S.-S. Rong F. Rosini Ch. Rosner Megan Ruan N. Salone A. Sarantsev Y. Schelhaas K. Schoenning M. Scodeggio W. Shan X. Shan Z.-J. Shang J. Shangguan L.-G. Shao M. Shao C.-P. Shen H.-F. Shen Wei Shen X.-Y. Shen B. Shi H. Shi J.-L. Shi J.-Y. Shi S.-Y. Shi X. Shi H. L. Song J. Song M. Song T. Song W. Song Y. Song Zi-Rong Song S. Sosio S. Spataro S. Stansilaus F. Stieler S.-S. Su G.-B. Sun G.-X. Sun H. Sun H.-K. Sun J.-F. Sun K. Sun L. Sun R. Sun S.-S. Sun T. Sun W.-Y. Sun Y.-C. Sun Y.-H. Sun Y.-J. Sun Y.-Z. Sun Z.-Q. Sun Z.-T. Sun C.-J. Tang G. Tang J. Tang J.-J. Tang L.-F. Tang Yao Tang L.-Y. Tao M. Tat J.-X. Teng J.-Y. Tian W.-H. Tian Yuan Tian Z.-F. Tian I. Uman B. Wang Bo Wang C. Wang Cong Wang D.-Y. Wang H.-J. Wang J. Wang J.-J. Wang J.-P. Wang K. Wang L.-L. Wang L.-W. Wang M. Wang N.-Y. Wang S. Wang Shun Wang T. Wang T.-J. Wang W. Wang W.-P. Wang X. Wang X.-F. Wang X.-L. Wang X.-N. Wang Xin Wang Y. Wang Y.-D. Wang Y.-F. Wang Y.-H. Wang Y.-J. Wang

Aug 2026 · 0 citations

Physics

Abstract

Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider, the Dalitz decay $\Sigma^0 \rightarrow \Lambda e^+e^-$ is studied experimentally for the first time. The $\Sigma^0$ hyperons are produced through the process $J/\psi \rightarrow \Sigma^0\bar{\Sigma}^0$ and analyzed using a double-tag method. The absolute branching fraction is measured to be $\mathcal{B}(\Sigma^0 \rightarrow \Lambda e^+e^-) = (6.34 \pm 0.25_{\rm stat.} \pm 0.23_{\rm syst.}) \times 10^{-3}$. This result shows a $2\sigma$ discrepancy from the theoretical calculation quoted in the PDG, where the uncertainties are statistical and systematic, respectively. In addition to the branching fraction, the transition magnetic moment $\mu$ is determined to be $(1.74 \pm 0.03_{\rm stat.} \pm 0.09_{\rm syst.})\,\mu_N$, where $\mu_N=e/(2m_p)$ represents the nucleon magnetic moment, providing valuable insight into the intrinsic structure of the $\Sigma^0$ hyperon.

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