2026-09-03 復旦大学
＜関連情報＞
- https://www.fudan.edu.cn/en/2026/0903/c344a150272/page.htm
- https://www.nature.com/articles/s41586-026-10818-8
偏極と量子もつれを通してバリオン半レプトン崩壊を探る Exploring baryon semileptonic decays through polarization and entanglement
The BESIII Collaboration
Nature Published:02 September 2026
DOI:https://doi.org/10.1038/s41586-026-10818-8
Abstract
The unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) matrix is a cornerstone of the standard model (SM). Precise tests of this unitarity require independent determinations of its elements, such as |Vus|, which governs the transition between strange and up quarks. Current measurements from kaon and tau decays show tensions that may hint at physics beyond the SM1,2,3. Hyperon semileptonic decays provide alternative probes but have remained largely untapped because previous experiments lacked sufficient kinematic information, making the measurements insensitive to the relevant form factors4. Here we report measurements of the axial-vector and weak-magnetism couplings, as well as the first determinations of the absolute branching fraction and weak-electricity coupling in Λ→pe–v–e, achieved by exploiting the polarization and quantum entanglement of ΛΛ–pairs produced at the J/ψ resonance. Combining our results with recent lattice quantum chromodynamics (QCD) calculations5 gives |Vus|LQCD = 0.2339 ± 0.0041, a model-independent determination consistent with CKM unitarity. By pioneering the exploitation of polarization and quantum entanglement in baryon semileptonic decays, our method enhances single-event sensitivity and is broadly applicable to other baryon semileptonic decays, establishing the foundation for a systematic research programme that can achieve precision comparable with that of kaon decays and provide a stringent independent test of the SM.
