Polarization and entanglement in baryon–antibaryon pair production in electron–positron annihilation

BESIII Collaboration

Research output: Contribution to journalLetterpeer-review

43 Citations (Scopus)

Abstract

Particles directly produced at electron–positron colliders, such as the J/ψ meson, decay with relatively high probability into a baryon–antibaryon pair 1 . For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase ΔΦ between the transition amplitudes to these helicity states results in a transverse polarization of the baryons 2–4 . From the joint angular distribution of the decay products of the baryons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of ΔΦ = 42.4 ± 0.6 ± 0.5° using Λ → pπ and Λ¯ → p¯ π + , n¯ π decays at BESIII. We find a value for the Λ → pπ decay parameter of α = 0.750 ± 0.009 ± 0.004, 17 ± 3% higher than the current world average, which has been used as input for all Λ polarization measurements since 1978 5,6 . For Λ¯ → p¯ π + we find α + = −0.758 ± 0.010 ± 0.007, giving A CP = (α + α + )/(α − α + ) = −0.006 ± 0.012 ± 0.007, a precise direct test of charge–parity symmetry (CP) violation in Λ decays.

Original languageEnglish
Pages (from-to)631-634
Number of pages4
JournalNature Physics
Volume15
Issue number7
DOIs
Publication statusPublished - 1 Jul 2019

Keywords

  • ANALYZING POWER
  • PARAMETER
  • J/PSI
  • DECAY
  • HYPERON
  • LAMBDA(LAMBDA)OVER-BAR
  • OBSERVABLES
  • E(+)E(-)
  • LAMBDA

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