Related Experiment Video
Updated: Oct 25, 2026

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser
Published on: June 28, 2018
Abstract:
Using (448.1±2.9)×106ψ(3686) events collected with the BESIII detector, we present the first complete determination of the spin density matrix in ψ(3686)→ΛΛ¯. This provides a unified framework to study both the production dynamics and the quantum correlations of the ΛΛ¯ system. From a five-dimensional joint angular analysis, we determine αψ=0.82±0.02stat.±0.01syst. and ΔΦ=20.6±3.6stat.±0.6syst.°. The non-zero phase implies a transverse polarization of Λ, with a maximum value of Py=0.074±0.013stat.±0.003syst. and a significance of 6.3σ. The same framework also gives access to the spin correlations of the baryon pair and enables tests of quantum nonclassicality. The average of the Bell nonlocality measure is determined to be m¯12=1.266±0.078stat.±0.049syst., yielding a violation of the Clauser-Horne-Shimony-Holt inequality with a significance of 3.7σ. These results establish ψ(3686)→ΛΛ¯ as a unique laboratory for unified studies of hadron production dynamics and quantum entanglement in a system of massive baryons.
Related Concept Videos
The Pauli Exclusion Principle
Atomic Nuclei: Nuclear Spin State Population Distribution
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Spin–Spin Coupling Constant: Overview
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Atomic Nuclei: Nuclear Spin State Overview

