A first measurement of the ΛΛand ΛΛ (ΛΛ) spin compositions in hadronic Z0decays

The spin composition of ΛΛ, ΛΛ and ΛΛpairs at low invariant mass values has been measured for the first time in multihadronic Z0decays with the OPAL detector at LEP. No single spin state has been observed in the ΛΛsample, 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 ΛΛpairs 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 ΛΛpairs, well above threshold, is found to be similar to that of the ΛΛsample. A ΛΛ emitter dimension is estimated from the data assuming the onset of the Pauli exclusion principle near threshold.