Measurement of hadron and lepton-pair production at 161 GeV<root s<172 GeV at LEP

Contains fulltext : 26256.pdf (publisher's version ) (Open Access

A Measurement of Pi-Polarization at Lep

Contains fulltext : 26223.pdf (publisher's version ) (Open Access

Measurement of the branching ratios b -&gt; e nu Chi, mu nu Chi, tau nu Chi, and nu Chi

The inclusive semileptonic branching ratios b --&gt; e nu X, mu nu X, tau nu X and nu X have been measured at LEP with the L3 detector. The analysis is based on 2-jet hadronic Z decays obtained in the data collected between 1991 and 1992. Three separate event samples are analysed, containing electrons, muons and large missing energy (neutrinos), respectively. From the electron sample, we measure Br(b --&gt; e nu X) = (10.89+/-0.20+/-0.51)% and, from the muon sample, Br(b --&gt; mu nu X) = (10.82+/-0.15+/-0.59)%, where the first error is statistical and the second is systematic. From the missing energy sample, we measure Br(b --&gt; nu X) = (23.08+/-0.77+/-1.24)%, assuming the relative semileptonic decay rates e:mu:tau = 1:1:(0.25+/-0.05), according to theoretical expectations. From a combined analysis of all three samples and constraining the relative semileptonic rates, we measure Br(b --&gt; e nu X) = Br(b --&gt; mu nu X) = (10.68+/-0.11+/-0.46)%. Alternatively, we can remove the constraint on the relative semileptonic rates and measure Br(b --&gt; tau nu X) = (1.7+/-0.5+/-1.1)%

Measurement of W-pair cross sections in e(+)e(-) interactions at root s=172 GeV and W-decay branching fractions RID C-4549-2008 RID C-5719-2008

We report on the measurement of W-boson pair-production with the L3 detector at LEP at an average centre-of-mass energy of 172.13 GeV. In a data sample corresponding to a total luminosity of 10.25 pb(-1) we select 110 four-fermion events with pairs of hadronic jets or leptons with high invariant masses. Branching fractions of W decays into different fermion-antifermion pairs are determined with and without the assumption of charged-current lepton universality. The branching fraction for hadronic W decays is measured to be: B(W --> hadrons) = 64.2(-3.8)(+3.7) (stat.) +/- 0.5 (syst.) %. Combining all final states the total cross section for W-pair production is measured to be: sigma(ww) = 12.27(-1.32)(+1.41) (stat.) +/- 0.23 (syst.) pb. The results are in good agreement with the Standard Model. (C) 1997 Elsevier Science B.V

Study of hadronic events and measurements of alpha(s) between 30 and 91 GeV RID C-4549-2008 RID C-5719-2008

We have studied the structure of hadronic events with a hard, isolated photon in the final state (e(+)e(-) --> Z --> hadrons + gamma) in the 3.6 million hadronic events collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed O/alpha(s)(2)/calculations to determine the strong coupling constant a, over a wide range of energies. We find that the strong coupling constant alpha(s) decreases with increasing energy, as expected from QCD. (C) 1997 Elsevier Science B.V