W + W − Hadronic Decay Properties

Recent measurements of the properties of W + W − events produced in e + e − collisions at √ s ∼ 183 GeV at LEP are reviewed. The data are used to investigate the predicted effects of final state interactions, specifically " colour reconnection ". 1 Motivation Hadronic data in e + e − collisions can be characterised by event shape distributions and inclusive observables such as charged particle multiplicities and momentum spectra. In addition to tests of Monte Carlo models, measurement of the properties of the hadronic sector of W + W − decays allows the question of 'colour reconnection' 1 to be addressed experimentally. The decay products of the two W decays may have a significant space-time overlap as the separation of their decay vertices at LEP2 energies is small compared to characteristic hadronic distance scales. In the fully hadronic channel this may lead to final state interactions. Colour reconnection is the general name applied to the case where such final state interactions lead to a rearrangement of the colour flow between the two W bosons. At present there is general consensus that observable effects of interactions between the colour singlets during the perturbative phase are expected to be small. In contrast, significant interference in the hadroni-sation process is considered to be a real possibility. With the current knowledge of non-perturbative QCD, such interference can be estimated only in the context of specific models. 1,2,3,4 One should be aware that other final state effects such as Bose-Einstein correlations between identical bosons may also influence the observed event properties. The combined action of these two effects may be either to reduce or enhance possible characteristic signatures of their presence.