A first measurement of the Λ$\Lambda$ and ΛΛ ($\Lambda$$\Lambda$) spin compositions in hadronic Z0 decays

The spin composition of Λ$\Lambda$, ΛΛ and $\Lambda$$\Lambda$ pairs at low invariant mass values has been measured for the first time in multihadronic Z⁰ decays with the OPAL detector at LEP. No single spin state has been observed in the Λ$\Lambda$ sample, verifying that the low mass enhancement in this sample, attributed to local baryon number compensation, is not a resonance state. The fraction of the spin 1 contribution to the Λ$\Lambda$ pairs was found to be consistent with the value 0.75, as expected from a statistical spin mixture. This may be the net effect of many different QCD processes which contribute to the hyperon anti-hyperon pair production. The spin composition of the identical ΛΛ and $\Lambda$$\Lambda$ pairs, well above threshold, is found to be similar to that of the Λ$\Lambda$ sample. A ΛΛ emitter dimension is estimated from the data assuming the onset of the Pauli exclusion principle near threshold.