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Cross-sections and angular distributions for hadronic and lepton pair final states in e+e− collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The results are used to measure the energy dependence of the electromagnetic coupling constant αem, and(More)
We have searched for unstable neutral and charged heavy leptons, N and L ± , and for excited states of neutral and charged leptons, ν * , e * , µ * and τ * , in e + e − collisions at centre-of-mass energies of 170 and 172 GeV using the OPAL detector at LEP. No evidence for their existence was found. From the analysis of charged-current decays of(More)
QCD coherence effects are studied based on measurements of correlations of particles with either restricted transverse momenta, p T < p cut T , where p T is defined with respect to the thrust axis, or restricted absolute momenta, p ≡ |p| < p cut , using about four million hadronic Z decays recorded at LEP with the OPAL detector. The correlations are(More)
The measurement of small–angle Bhabha scattering is used to determine the luminosity at the OPAL interaction point for the LEP I data recorded between 1993 and 1995. The measurement is based on the OPAL Silicon-Tungsten Luminometer which is composed of two calorimeters encircling the LEP beam pipe, on opposite sides of the interaction point. The luminometer(More)
Production of events with hadronic and leptonic final states has been measured in e+e− collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Zγ events, and compared to Standard Model(More)
Searches for a scalar top quark and a scalar bottom quark have been performed using a data sample of 438 pb at centre-of-mass energies of √ s =192 – 209 GeV collected with the OPAL detector at LEP. No evidence for a signal was found. The 95% confidence level lower limit on the scalar top quark mass is 97.6 GeV if the mixing angle between the supersymmetric(More)
A search for pair-produced doubly charged Higgs bosons has been performed using data samples corresponding to an integrated luminosity of about 614 pb −1 collected with the OPAL detector at LEP at centre-of-mass energies between 189 GeV and 209 GeV. No evidence for a signal has been observed. A mass limit of 98.5 GeV/c 2 at the 95% confidence level has been(More)