371 research outputs found
An Upper Limit on the Branching Ratio for
No full textWe have searched for decays of the ø lepton into seven or more charged particles, using data collected with the OPAL detector from 1990 to 1995 in e + e \Gamma collisions at p s ß MZ . No candidate events were found and an upper limit on the branching ratio for ø decays into seven charged particles of 1:8 \Theta 10 \Gamma5 at the 95% confidence level was determined. (Accepted by Physics Letters B) The OPAL Collaboration K. Ackerstaff 8 , G. Alexander 23 , J. Allison 16 , N. Altekamp 5 , K.J. Anderson 9 , S. Anderson 12 , S. Arcelli 2 , S. Asai 24 , D. Axen 29 , G. Azuelos 18;a , A.H. Ball 17 , E. Barberio 8 , R.J. Barlow 16 , R. Bartoldus 3 , J.R. Batley 5 , S. Baumann 3 , J. Bechtluft 14 , C. Beeston 16 , T. Behnke 8 , A.N. Bell 1 , K.W. Bell 20 , G. Bella 23 , S. Bentvelsen 8 , P. Berlich 10 , S. Bethke 14 , O. Biebel 14 , A. Biguzzi 5 , S.D. Bird 16 , V. Blobel 27 , I.J. Bloodworth 1 , J.E. Bloomer 1 , M. Bobins..
Measurement of alpha(s) with radiative hadronic events.
No full textHadronic final states with a hard isolated photon are studied using data taken at centre-of-mass energies around the mass of the Z boson with the OPAL detector at LEP. The strong coupling alpha(s) is extracted by comparing data and QCD predictions for event shape observables at average reduced centre-of-mass energies ranging from 24 GeV to 78 GeV, and the energy dependence of alpha(s) is studied. Our results are consistent with the running of alpha(s) as predicted by QCD and show that within the uncertainties of our analysis event shapes in hadronic Z decays with hard and isolated photon radiation can be described by QCD at reduced centre-of-mass energies. Combining all values from different event shape observables and energies gives alpha(s)(M-Z)=0.1182 +/- 0.0015(stat.)+/- 0.0101(syst.)
Production of Fermion-pair Events in e
No full textCross-sections for hadronic and leptonic two-fermion events, and leptonic forwardbackward asymmetries, have been measured in e + e \Gamma collisions at a centre-of-mass energy of 161 GeV, using the OPAL detector at LEP. Results are presented both including and excluding the dominant production of radiative flZ 0 events. We have measured R b , the ratio of the number of bb to all multihadronic events at 161 GeV, and compared it to the result obtained at 130--136 GeV. All results agree well with the Standard Model expectations. In a model-independent fit to the Z 0 lineshape, the data presented here give an improved precision on the flZ 0 -interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by effective four-fermion contact interactions. Submitted to Physics Letters B The OPAL Collaboration K. Ackerstaff 8 , G. Alexander 23 , J. Allison 16 , N. Altekamp 5 , K. Ametewee 25 , K.J. Anderson 9 , S. Anderso..
- …
