Probing CP symmetry and weak phases with entangled double-strange baryons

The BESIII Collaboration

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter–antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon–antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ baryon and its antiparticle2Ξ¯+, has enabled a direct determination of the weak-phase difference, (ξP − ξS) = (1.2 ± 3.4 ± 0.8) × 10−2 rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Λ decay parameter αΛ (refs. 4,5). The ΛΛ¯ asymmetry is in agreement with and compatible in precision to the most precise previous measurement4.

Original languageEnglish (US)
Pages (from-to)64-69
Number of pages6
Issue number7912
StatePublished - Jun 2 2022

Bibliographical note

Funding Information:
The BESIII collaboration thanks the staff of BEPCII and the IHEP Computing Centre for their strong support. This work is supported in part by the National Key Research and Development Program of China under contract nos 2020YFA0406300 and 2020YFA0406400; the National Natural Science Foundation of China (NSFC) under contract nos 11625523, 11635010, 11735014, 11822506, 11835012, 11905236, 11935015, 11935016, 11935018, 12075107 and 11961141012; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under contract nos U1732263 and U1832207; the CAS Key Research Program of Frontier Sciences under contract nos QYZDJ-SSW-SLH003 and QYZDJ-SSW-SLH040; the 100 Talents Program of CAS; the CAS President’s International Fellowship Initiative (PIFI) programme; INPAC and Shanghai Key Laboratory for Particle Physics and Cosmology; the Shanghai Pujiang Program (20PJ1401700); the ERC under contract no. 758462; the European Union Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 894790; the German Research Foundation (DFG) under contract nos 443159800, Collaborative Research Center (CRC) 1044, FOR 2359, GRK 214; the Istituto Nazionale di Fisica Nucleare, Italy; the Ministry of Development of Turkey under contract no. DPT2006K-120470; the National Science and Technology fund; the Olle Engkvist Foundation under contract no. 200-0605; STFC (United Kingdom); The Knut and Alice Wallenberg Foundation (Sweden) under contract no. 2016.0157; The Royal Society, UK under contract nos DH140054 and DH160214; the Swedish Research Council; the US Department of Energy under contract nos DE-FG02-05ER41374 and DE-SC-0012069; and the National Science Centre (Poland) under contract no. 2019/35/O/ST2/02907.

Publisher Copyright:
© 2022, The Author(s).


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