Colour reconnection in e+e- -> W+W- at sqrt(s) = 189 - 209 GeV

TL;DR

This study investigates colour reconnection effects in W+W- decays at LEP energies, testing models against particle multiplicity and angular distributions, and finds data favor moderate reconnection probabilities.

Contribution

It provides experimental constraints on colour reconnection models, especially excluding extreme scenarios and quantifying reconnection probability at LEP energies.

Findings

Extreme SK-I model scenarios are excluded by data.

Best fit reconnection probability in SK-I model is 37%.

Charged particle multiplicity in W decays measured as 19.38 with small uncertainties.

Abstract

The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range sqrt(s) ~ 189-209 GeV using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of W+W-. Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude extreme scenarios of the Sjostrand-Khoze Type I (SK-I) model and are compatible with other models, both with and without colour reconnection effects. In the context of the SK-I model, the best agreement with data is obtained for a reconnection probability of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to be (nqqch) = 19.38+-0.05(stat.)+-0.08 (syst.).