A study of four-fermion final states with high multiplicity at LEP

Abstract A search for l + l − q q (l = e, μ ) four-fermion final states in high multiplicity events has been performed at s ≈m Z and above the Z peak at s =130 GeV and s =136 GeV. The data taken with OPAL correspond to an integrated luminosity of 132.4 pb −1 and 5.3 pb −1 at s ≈m Z and s =130−136 GeV, respectively. While at the Z resonance the data are in good agreement with the Standard Model predictions, we find more events than expected at s =130−136 GeV, especially in the μ + μ − q q channel, where 5 events remain after all cuts, with only 0.6 predicted by the Monte Carlo simulation. For all center-of-mass energies the observed shapes of the differential distributions are consistent with the predictions.