The process
e
+
e
−→
Zγγ→
q
q
̄
γγ
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/
Λ
2<0.005 GeV
−2 and −0.007 GeV
−2<
a
c
/
Λ
2<0.011 GeV
−2, at 95% confidence level.
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
β for two scalar top mixing hypotheses. For tan
β greater than 0.8, they are
m
h>83.4 GeV and
m
A>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 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.
The production of c and b quarks
γγ collisions is studied with the L3 detector at LEP with 410 pb
−1 of data, collected at centre-of-mass energies from 189 GeV to 202 GeV. Hadronic final states ...containing c and b quarks are identified by detecting electrons or muons from their semileptonic decays. The cross sections
σ(
e
+
e
−→
e
+
e
−
c
c
̄
X)
and
σ(
e
+
e
−→
e
+
e
−
b
b
̄
X)
are measured and compared to next-to-leading order perturbative QCD calculations. The cross section of b production is measured in
γγ collisions for the first time. It is in excess of the QCD prediction by a factor of three.
A search for chargino, neutralino and scalar lepton pair-production in e+e- collisions at the centre-of-mass energy of 189 GeV is performed under the assumptions that R-parity is not conserved in ...decays and only one of the coupling constants lambda_ijk, lambda'_ijk or lambda''_ijk is non-negligible. No signal is found in a data sample corresponding to an integrated luminosity of 176.4 pb-1. Limits on the production cross sections, on the Minimal Supersymmetric Standard Model parameters and on the masses of the supersymmetric particles are derived.
The K
0
SK
0
S final state in two-photon collisions is studied with the L3 detector at LEP. The mass spectrum is dominated by the formation of the
f
′
2
(1525) tensor meson in the helicity-two state ...with a two-photon width times the branching ratio into
K
K
̄
of 76±6±11 eV. A clear signal for the formation of the f
J(1710) is observed and it is found to be dominated by the spin-two helicity-two state. No resonance is observed in the mass region around 2.2 GeV and an upper limit of 1.4 eV at 95% C.L. is derived for the two-photon width times the branching ratio into K
0
SK
0
S for the glueball candidate
ξ(2230).
The e
+e
−→e
+e
−K
S
0K
±
π
∓ and e
+e
−→e
+e
−
ηπ
+
π
− final states are studied with the L3 detector at LEP using data collected at centre-of-mass energies from 183 GeV up to 202 GeV. The mass ...spectrum of the
K
0
SK
±
π
∓ final state shows an enhancement around 1470 MeV, which is identified with the pseudoscalar meson
η(1440). This state is observed in
γγ collisions for the first time and its two-photon width is measured to be
Γ
γγ(η(1440))×
BR(η(1440)→
K
K
̄
π)=212±50 (
stat.)±23
(sys.) eV. Clear evidence is also obtained for the formation of the axial vector mesons f
1(1420) and f
1(1285). In the
ηπ
+
π
− channel the f
1(1285) is observed, and upper limits for the formation of
η(1440) and
η(1295) are obtained.
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.
The data collected by the L3 experiment at LEP at a centre-of-mass energy of 188.6 GeV are used to measure the W-pair production cross section and the W-boson decay branching fractions. These data ...correspond to an integrated luminosity of 176.8pb^-1. The total cross section for W-pair production, combining all final states, is measured to be sigma_WW = 16.24 +/- 0.37(stat.) +/- 0.22(syst.) pb. Including our data collected at lower centre-of-mass energies, the hadronic branching fraction of the W-boson is determined to be B(W ->qq) = 68.20 +/- 0.68 (stat.) +/- 0.33 (syst.) %. The results agree with the Standard Model predictions.
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