Colour reconnection studies in e+e−→W+W− at s=183 GeV

The predicted effects of final state interactions such as colour reconnection are investigated by measuring properties of hadronic decays of W bosons, recorded at a centre-of-mass energy of s≃182.7 GeV in the OPAL detector at LEP. Dependence on the modelling of hadronic W decays is avoided by comparing W+W−→qq′qq′ events with the non-leptonic component of W+W−→qq′ℓνℓ events. The scaled momentum distribution, its mean value, 〈xp〉, and that of the charged particle multiplicity, 〈nch〉, are measured and found to be consistent in the two channels. The measured differences are:Δ〈nch〉=〈nch4q〉−2〈nchqqℓν〉=+0.7±0.8±0.6Δ〈xp〉=〈xp4q〉−〈xpqqℓν〉=(−0.09±0.09±0.05)×10−2.In addition, measurements of rapidity and thrust are performed for W+W−→qq′qq′ events. The data are described well by standard QCD models and disfavour one model of colour reconnection within the ARIADNE program. The current implementation of the Ellis-Geiger model of colour reconnection is excluded. At the current level of statistical precision no evidence for colour reconnection effects was found in the observables studied. The predicted effect of colour reconnection on OPAL measurements of MW is also quantified in the context of models studied.