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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)
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)
Photonic events with large missing energy have been observed in e + e − collisions at centre-of-mass energies of 130, 136 and 183 GeV collected in 1997 using the OPAL detector at LEP. Results are presented for event topologies with a single photon and missing transverse energy or with an acoplanar photon pair. Cross-section measurements are performed within(More)
Gluon jets are identified in ee hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent(More)
G. Abbiendi, C. Ainsley, P. F. Åkesson, G. Alexander, J. Allison, P. Amaral, G. Anagnostou, K. J. Anderson, S. Asai, D. Axen, G. Azuelos, I. Bailey, E. Barberio, T. Barillari, R. J. Barlow, R. J. Batley, P. Bechtle, T. Behnke, K. W. Bell, P. J. Bell, G. Bella, A. Bellerive, G. Benelli, S. Bethke, O. Biebel, O. Boeriu, P. Bock, M. Boutemeur, S. Braibant, L.(More)
A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at [Formula: see text], corresponding to an integrated luminosity of approximately 600 pb-1. Charged Higgs bosons are assumed to be pair-produced and to decay into [Formula:(More)