Exploring baryon semileptonic decays through polarization and entanglement

by Prof. Tao Luo（罗涛） (复旦大学)

Friday 18 Sept 2026, 12:00 → 13:30 Asia/Shanghai

5#/6th-603 - Meeting Room 603 (Science Building)

Abstract:

This report will present our latest research results on the β decay of the Λ hyperon through polarization and quantum entanglement, based on 10 billion J/ψ events collected by the BESIII experiment.
The CKM matrix element |𝑉_𝑢𝑠 | is a key parameter for testing the three-generation quark mixing mechanism and the unitarity of the CKM matrix. However, current measurements of |𝑉_𝑢𝑠 |  from different decay channels show significant discrepancies, and exhibit some tension with theoretical predictions, urgently calling for independent cross-check methods. The β decay of the Λ hyperon is one of the ideal places to study |𝑉_𝑢𝑠 |, but the final-state antineutrino cannot be directly detected, leading to the loss of key kinematic information; this field has thus failed to achieve high-precision breakthroughs for over thirty years.
To address these difficulties, based on ten billion J/ψ events collected by the BESIII experiment, we exploit the quantum entanglement inherent in the production of hyperon–antihyperon pairs, and infer unknown physical information from observable particle signals, effectively compensating for the observational blind spots. We have developed a joint angular distribution multivariate fitting method that analyzes the production, polarization, quantum entanglement, and decay of Λ and anti-Λ as a complete unified process, and reconstructs the kinematic information of the antineutrino using energy–momentum conservation. By combining the "visible" and "invisible" information, we successfully extracted |𝑉_𝑢𝑠 |, and for the first time measured the absolute branching fraction of Λ hyperon β decay, the weak-electric coupling parameters, and multiple decay parameters of the anti-Λ, filling several experimental gaps. The related paper was published in Nature.

Biography:

Luo Tao is a professor and doctoral supervisor at Fudan University. He received his Ph.D. from the Institute of High Energy Physics, Chinese Academy of Sciences, in 2011, and joined Fudan University in 2017. He has been selected for the Shanghai Pujiang Talent Program and the Young Scholars of the National Major Talent Project. Over the past five years, he has published more than twenty JCR Q1 SCI papers based on the BESIII experiment, including one in Nature and nine in Physical Review Letters. His current research focuses on experimental studies at BESIII, including hyperon semileptonic decays, hyperon excited states, charmed meson physics, and charmonium transitions. In 2025, one of his doctoral students was selected for the 16th "Academic Star" of Fudan University (only 10 students across all science and engineering disciplines university-wide each year).

Host: Prof. Wei Wang

Alternative online link: https://meeting.tencent.com/dm/0pI4Vl2fKdiO

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