Fermi-Dirac correlations in Lambda pairs in hadronic Z decays

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doi:10.1016/S0370-2693(00)00080-0

Two-particle correlations of Lambda Lambda and <(Lambda)over bar><(Lambda)over bar> 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 Lambda 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 Lambda<(Lambda)over bar> 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. (C) 2000 Elsevier Science B.V. All rights reserved.