Precise Measurements of Decay Parameters and CP Asymmetry with Entangled Λ-Λ[over ¯] Pairs

Area of Science:

• Particle Physics
• Quantum Chromodynamics (QCD)
• Hadron Spectroscopy

Background:

• CP violation is a key concept in the Standard Model, explaining matter-antimatter asymmetry.
• Baryon decays offer a sensitive probe for studying CP violation beyond the Standard Model.
• Previous studies on Lambda (Λ) decays have provided insights but require higher precision.

Purpose of the Study:

• To search for CP violation in Lambda (Λ) decay by precisely measuring decay parameters.
• To determine the CP asymmetry (A_CP) in the process e⁺e⁻ → J/ψ → ΛΛ̄.
• To provide precise decay parameters for future studies of strange, charmed, and beauty baryons.

Main Methods:

• Analysis of 10 billion J/ψ events collected at the BESIII experiment.
• Utilizing the e⁺e⁻ → J/ψ → ΛΛ̄ process.
• Performing a five-dimensional fit to the angular distributions of the daughter baryon (Λ and Λ̄).

Main Results:

• The most precise values for the decay parameters α⁻ (for Λ→pπ⁻) and α⁺ (for Λ̄→p̄π⁺) were determined.
• The averaged decay parameter α_avg was extracted with unprecedented accuracy.
• The CP asymmetry A_CP was measured to be -0.0025±0.0046±0.0012, consistent with CP symmetry.

Conclusions:

• The precise measurements of Λ decay parameters contribute significantly to the field of particle physics.
• The results provide a benchmark for theoretical calculations and future experimental searches for CP violation.
• This study enhances our understanding of fundamental symmetries in the baryon sector.