Spin polarization and quantum entanglement of baryon-antibaryon pairs produced in electron-positron annihilation

TL;DR

This paper analyzes how spin polarization and quantum entanglement evolve in baryon-antibaryon pairs produced in electron-positron annihilation, providing analytical tools and revealing conditions for polarization and entanglement.

Contribution

It introduces a fully analytical spin density matrix formalism for baryon-antibaryon pairs and extends it to multi-step cascade decays, highlighting conditions for polarization and entanglement.

Findings

Maximal parity violation leads to fully polarized, non-entangled particles.

Quantum entanglement is amplified in charge-conjugate decays under CP conservation.

Analytical recursive relations simplify density matrix calculations.

Abstract

In this work, we systematically investigate the evolution of spin polarization and quantum entanglement in cascade decays of baryon-antibaryon pairs, which are produced in electron-positron annihilation. We derive a fully analytical spin density matrix explicitly expressed in terms of spin polarization observables, extend this formalism to multi-step cascade decay scenarios, and establish compact recursive relations to facilitate density matrix calculations for such processes. It is found that when maximal parity violation occurs during a decay, the resulting final-state particles are fully polarized and exist in a non-entangled state. Furthermore, we demonstrate that quantum entanglement amplification is a generic characteristic of charge-conjugate decays under $CP$ conservation when the initially produced baryon-antibaryon pair is polarized.