Spin alignment of leading K∗(892)0 mesons in hadronic Z0 decays

Helicity density matrix elements for inclusive K∗(892)0 mesons from hadronic Z0 decays have been measured over the full range of K∗ 0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum xp values above 0.3, with the matrix element ϱ00 rising to 0.66 ± 0.11 for xp > 0.7. The values of the real part of the off-diagonal element ϱ1 - 1 are negative at large xp, with a weighted average value of −0.09 ± 0.03 for xp > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq system from the Z0 decay. All other helicity density matrix elements measured are consistent with zero over the entire xp range. The K∗ 0 fragmentation function has also been measured and the total rate determined to be 0.74 ± 0.02 ± 0.02 K∗(892)0 mesons per hadronic Z0 decay.