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

Measurement of hadron and lepton-pair production at 130 GeV<root s<140 GeV at LEP

We report on the first measurements of e(+)e(-) annihilations into hadrons and lepton pairs at centre-of-mass energies between 130 GeV and 140 GeV. In a total luminosity of 5 pb(-1) collected with the L3 detector at LEP we select 1577 hadronic and 401 lepton-pair events. The measured cross sections and leptonic forward-backward asymmetries agree well with the Standard Model predictions

Search for supersymmetric particles at 130 GeV<root s<140 GeV at LEP

Contains fulltext : 26248.pdf (publisher's version ) (Open Access

Search for neutral Higgs boson production through the process e(+)e(-)->Z(*)H(0)

The results of the searches for neutral Higgs boson production in the process e(+)e(-) --> Z* H-0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z(0) decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doubler Model and limits on the nonstandard Higgs boson production through the process e(+)e(-) --> Z*h(0) are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state

Inclusive J, Psi' and Chi(c) production in hadronic Z decays

We report on measurements of the inclusive production of J, psi' and chi(c) mesons in hadronic Z decays, based on 3.2 million hadronic events collected using the L3 detector at LEP. The J and psi' mesons are reconstructed through their decays into lepton pairs, while the chi(c) mesons are reconstructed via the decay mode chi(c) --> J + gamma. The measured branching fractions are: Br(Z --> J + X) = (3.40 +/- 0.23 (stat.) +/- 0.27 (sys.)) x 10(-3), Br(Z --> psi' + X) = (1.6 +/- 0.5 (stat.) +/- 0.3 (sys.)) x 10(-3) Br(Z --> chi(cl) + X) = (2.7 +/- 0.6 (stat.) +/- 0.5 (sys.)) x 10(-3). In the absence of a clear chi(c2) signal, the upper limit at 90% C.L. is set: Br(Z --> chi(c2) + X) < 3.2 x 10(-3). (C) 1997 Elsevier Science B.V

Measurement of the B-d(0) meson oscillation frequency

Time-dependent B-d(0)-(B) over bar(d)(0) mixing is studied using 1.5 million hadronic Z decays collected by L3. Semileptonic B decays are selected by requiring at least one reconstructed lepton in both thrust hemispheres. Charge correlations between the tagged leptons are studied as a function of proper time. The proper time of the b-hadron decay is measured by reconstructing the production and decay vertices using a silicon microvertex detector: The measured B-d(0) meson oscillation frequency corresponds to a mass difference Delta m(d) between the two B-d(0) mass eigenstates of Delta m(d) = (0.496(-0.051)(+0.053) (stat) +/- 0.043 (syst)) ps(-1)

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)%