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

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

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

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

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)

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

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