The lifetime of the tau lepton is measured using data collected in 1994 by the L3 detector at LEP. The precise track position information of the Silicon Microvertex Detector is exploited. The tau ...lepton lifetime is determined from the signed impact parameter distribution for 30 322 tau decays into one charged particle and from the decay length distribution for 3891 tau decays into three charged particles. Combining the two methods we obtain $\tau_{\tau}$ = 290.1 $\pm$ 4.0 fs.
The cross section for open-beauty production in photon–photon collisions is measured using the whole high-energy and high-luminosity data sample collected by the L3 detector at LEP. This corresponds ...to 627 pb$^−1$ of integrated luminosity for electron–positron centre-of-mass energies from 189 to 209 GeV. Events containing b quarks are identified through their semi-leptonic decay into electrons or muons. The $e^+e^- _ rightarrow $e^+e^-bb^-X$ cross section is measured within our fiducial volume and then extrapolated to the full phase space. These results are found to be in significant excess with respect to Monte Carlo predictions and next-to-leading order QCD calculations.
The e$^+e^- \to e^+e^-$ hadrons reaction, where one of the two electrons is detected in a low polar-angle calorimeter, is analysed in order to measure the hadronic photon structure function ...$F^\gamma_2$ . The full high-energy and high-luminosity data set, collected with the L3 detector at centre-of-mass energies 189 GeV $\leq \sqrt{s} \leq$ 209 GeV, corresponding to an integrated luminosity of 608/pb is used. The Q$^2$ range 11 GeV$^2 \leq Q^2$ 34 GeV$^2$ and the $x$ range 0.006$\leq x \leq$ 0.556 are considered. The data are compared with recent parton density functions.
The absolute muon flux between 20 GeV and 300 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 degree to 58 degrees. Due to the large exposure of about 150 m2 ...sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3% at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 GeV and 500 GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003 (stat.)+- 0.019 (syst.).
Single top production in e+e− annihilations is searched for in data collected by the L3 detector at centre-of-mass energies from 189 to 209 GeV, corresponding to a total integrated luminosity of ...634 pb−1. Investigating hadronic and semileptonic top decays, no evidence of single top production at LEP is obtained and upper limits on the single top cross section as a function of the centre-of-mass energy are derived. Limits on possible anomalous couplings, as well as on the scale of contact interactions responsible for single top production are determined.
The process e^+e^- -> Z gamma gamma -> q q~ gamma gamma$ is studied in 0.5\,fb-1$ of data collected with the L3 detector at centre-of-mass energies between 130.1 GeV and 201.7 GeV. Cross sections are ...measured and found to be consistent with the Standard Model expectations. The study of the least energetic photon constrains the quartic gauge boson couplings to -0.008 GeV-2 a_0/\Lambda^2 0.005 GeV-2 and -0.007 GeV-2 a_c/\Lambda^2 0.011 GeV-2, at 95% confidence level.
The cross section for the production of Z boson pairs is measured using the data collected by the L3 detector at LEP in 1999 in e^+e^- collisions at centre-of-mass energies ranging from 192 GeV up to ...202 GeV. Events in all the visible final states are selected, measuring the cross section of this process. The special case of final states containing b quarks is also investigated. All results are in agreement with the Standard Model predictions.
A search for the lightest neutral CP-even and the neutral CP-odd Higgs bosons of the Minimal Supersymmetric Standard Model is performed using 233.2 pb-1 of integrated luminosity collected with the L3 ...detector at LEP at centre-of-mass energies 192-202 GeV. No signal is observed and lower mass limits are given as a function of tan(beta) for two scalar top mixing hypotheses. For tan(beta) greater than 0.8, they are mh 83.4 GeV and mA 83.8 GeV at 95 % confidence level.
Excited leptons are searched for using the L3 detector at LEP. The data collected at centre-of-mass energies in the range from 192 up to 202 GeV correspond to a total luminosity of 233 $\rm pb^{-1}$. ...No evidence of either pair production of excited leptons, nor of single production is found. From the searches for pair produced excited leptons, lower mass limits close to the kinematic limit are set. From the searches for singly produced excited leptons, upper limits on their couplings are derived in the mass range up to 200 GeV.
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