Measurement of Λ polarization from Ζ decays

ALEPH Collaboration

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The polarization of Λ baryons from Ζ decays is studied with the ALEPH apparatus. Evidence of longitudinal polarization of s quarks from Ζ decay is observed for the first time. The measured longitudinal Λ polarization is PΛL = -0.32 ± 0.07 for z = p/pbeam > 0.3. This agrees with the prediction of -0.39 ± 0.08 from the standard model and the constituent quark model, where the error is due to uncertainties in the mechanism for Λ production. The observed Λ polarization is diluted with respect to the primary s quark polarization by Λ baryons without a primary s quark. Measurements of the Λ forward-backward asymmetry and of the correlation between back-to-back ΛΛ̄ pairs are used to check this dilution. In addition the transverse Λ polarization is measured. An indication of transverse polarization, more than two standard deviations away from zero, is found along the normal to the plane defined by the thrust axis and the Λ direction.

Original languageEnglish (US)
Pages (from-to)319-330
Number of pages12
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Issue number4
StatePublished - May 9 1996
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics


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