Fermi–Dirac correlations in Λ pairs in hadronic Z decays

Two-particle correlations of ΛΛ and Λ̄Λ̄ pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q<2 GeV which could arise from the effects of Fermi–Dirac statistics. In addition the spin content of the Λ pair system has been determined. For Q>2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q<2 GeV this fraction is found to be lower. For ΛΛ̄ pairs, where no Fermi–Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range.