107 research outputs found
Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV
A search for the lightest neutral scalar and neutral pseudoscalar Higgs
bosons in the Minimal Supersymmetric Standard Model is performed using 176.4
pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of
189 GeV. No signal is observed, and the data are consistent with the expected
Standard Model background. Lower limits on the masses of the lightest neutral
scalar and pseudoscalar Higgs bosons are given as a function of tan(beta).
Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h
> 77.1 GeV and m_A > 77.1 GeV
Measurement of the Lifetime of the Tau Lepton
The tau lepton lifetime is measured with the L3 detector at LEP using the
complete data taken at centre-of-mass energies around the Z pole resulting in
tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result
with the muon lifetime supports lepton universality of the weak charged current
at the level of six per mille. Assuming lepton universality, the value of the
strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/-
0.015(exp.) +/- 0.014 (theory)
Search for Extra Dimensions in Boson and Fermion Pair Production in e+e- Interactions at LEP
Extra spatial dimensions are proposed by recent theories that postulate the
scale of gravity to be of the same order as the electroweak scale. A sizeable
interaction between gravitons and Standard Model particles is then predicted.
Effects of these new interactions in boson and fermion pair production are
searched for in the data sample collected at centre-of-mass energies above the
Z pole by the L3 detector at LEP. In addition, the direct production of a
graviton associated with a Z boson is investigated. No statistically
significant hints for the existence of these effects are found and lower limits
in excess of 1 TeV are derived on the scale of this new theory of gravity
Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays
We have measured the probability, n(g->cc~), of a gluon splitting into a
charm-quark pair using 1.7 million hadronic Z decays collected by the L3
detector. Two independent methods have been applied to events with a three-jet
topology. One method relies on tagging charmed hadrons by identifying a lepton
in the lowest energy jet. The other method uses a neural network based on
global event shape parameters. Combining both methods, we measure n(g->cc~)=
[2.45 +/- 0.29 +/- 0.53]%
Measurement of Triple-Gauge-Boson Couplings of the W Boson at LEP
We report on measurements of the triple-gauge-boson couplings of the W boson
in e+e- collisions with the L3 detector at LEP. W-pair, single-W and
single-photon events are analysed in a data sample corresponding to a total
luminosity of 76.7 pb^{-1} collected at centre-of-mass energies between 161 GeV
and 183 GeV. CP-conserving as well as both C- and P-conserving
triple-gauge-boson couplings are determined. The results, in good agreement
with the Standard-Model expectations, confirm the existence of the self
coupling among the electroweak gauge bosons and constrain its structure
Measurement of Hadron and Lepton-Pair Production at 130GeV < \sqrt{s} < 189 GeV at LEP
We report on measurements of e+e- annihilation into hadrons and lepton pairs.
The data have been collected with the L3 detector at LEP at centre-of-mass
energies between 130 and 189 GeV. Using a total integrated luminosity of 243.7
pb^-1, 25864 hadronic and 8573 lepton-pair events are selected for the
measurement of cross sections and leptonic forward-backward asymmetries. The
results are in good agreement with Standard Model predictions
Measurement of Mass and Width of the W Boson at LEP
We report on measurements of the mass and total decay width of the W boson
with the L3 detector at LEP. W-pair events produced in
interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in
a data sample corresponding to a total luminosity of 76.7 pb. Combining
all final states in W-pair production, the mass and total decay width of the W
boson are determined to be GeV and
GeV, respectively
Measurement of the Photon Structure Function at High Q^2 at LEP
The structure functions of real and virtual photons are derived from cross
section measurements of the reaction e^+e^ -> e^+e^- + hadrons at LEP. The
reaction is studied at \sqrt{s} ~ 91 GeV with the L3 detector. One of the final
state electrons is detected at a large angle relative to the beam direction,
leading to Q^2 values between 40 GeV^2 and 500 GeV^2. The other final state
electron is either undetected or it is detected at a four-momentum transfer
squared P^2 between 1 GeV^2 and 8 GeV^2. These measurements are compared with
predictions of the Quark Parton Model and other QCD based models
Search for Heavy Neutral and Charged Leptons in ee Annihilation at = 183 and 189 GeV
A search for unstable neutral and charged heavy leptons as well as for stable
charged heavy leptons is performed at center-of-mass energies = 183
and 189 GeV with the L3 detector at LEP. No evidence for their existence is
found. We exclude neutral heavy leptons which couple to the electron, muon or
tau family, of the Dirac type for masses below 92.4, 93.3 and 83.3 GeV, and of
the Majorana type for masses below 81.8, 84.1 and 73.5 GeV, respectively. We
exclude unstable charged heavy leptons for masses below 93.9 GeV for a wide
range of the associated neutral heavy lepton mass. If the unstable charged
heavy lepton decays to a light neutrino, we exclude masses below 92.4 GeV. The
production of stable charged heavy leptons with mass less than 93.5 GeV is also
excluded
Measurement of an Elongation of the Pion Source in Z Decays
We measure Bose-Einstein correlations between like-sign charged pion pairs in
hadronic Z decays with the L3 detector at LEP. The analysis is performed in
three dimensions in the longitudinal center-of-mass system. The pion source is
found to be elongated along the thrust axis with a ratio of transverse to
longitudinal radius of
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