We search for anomalous $\ZZG$ and $\ZGG$ couplings with the L3 detector at LEP. The analysis is based on the study of the process $\EEZG$ at center-of-mass energies in the range $161 \GeV \rts 183 ...\GeV$. No evidence for anomalous effects is found. Limits at the 95\% confidence level are set on the values of the eight possible anomalous couplings. Depending on the type of coupling new physics scales below 213 GeV to 1083 GeV are excluded.
We search for anomalous ZZ
γ and Z
γγ couplings with the L3 detector at LEP. The analysis is based on the study of the process e
+e
+→Z
γ at center-of-mass energies in the range
161
GeV
<
s
<183
GeV
.... No evidence for anomalous effects is found. Limits at the 95% confidence level are set on the values of the eight possible anomalous couplings. Depending on the type of coupling new physics scales below 213 GeV to 1083 GeV are excluded.
Two-photon formation of the charmonium resonance
χ
c2 has been studied with the L3 detector at LEP. The
χ
c2 is identified through its decay
χ
c2→
γJ/
ψ, with a subsequent decay J/
ψ→e
+e
− or J/
ψ→μ
...+μ
−. With an integrated luminosity of 140 pb
−1 at
s
≃
91
GeV
and 52 pb
−1 at
s
≃
183
GeV
, we measure the two-photon width of the
χ
c2 to be
Γ
γγ(χ
c2
)=1.02±0.40
(stat.)
±0.15
(sys.)
±0.09(
BR.)
keV
.
We have studied the structure of hadronic events with a hard, %radiated isolated photon in the final state ($\mathrm{e^{+}e^{-}} \rightarrow$ Z $\rightarrow$ hadrons $+$ $\gamma$) in the 3.6 million ...hadronic data collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed $\cal{O} \alpha_{s}^{2})$ calculations to determine the strong coupling constant $\alpha_{s}$ over a wide range of energies. We find that the strong coupling constant $\alpha_{s}$ decreases with increasing energy, as expected from QCD.
The reactions e
+e
−→ e
+e
−e
+e
− and e
+e
−→ e
+e
−μ
+μ
−, in a single tag configuration, are studied at LEP with the L3 detector. The data set corresponds to an integrated luminosity of 93.7 pb
−1 ...at
s
=91
GeV. Differential cross sections are measured for
1.4
GeV
2≤Q
2≤7.6
GeV
2
. The leptonic photon structure function
F
γ
2 and azimuthal correlations are measured for e
+e
−→ e
+e
−μ
+μ
−. The related structure functions
F
γ
A
and
F
γ
B
, which originate from interference terms of the scattering amplitudes, are determined for the first time.
The reaction e+e−→e+e−γ∗γ∗→e+e−hadrons for quasi-real photons is studied using data from s=183 GeV up to 202 GeV. Results on the total cross sections σ(e+e−→e+e−hadrons) and σ(γγ→hadrons) are given ...for the two-photon centre-of-mass energies 5 GeV⩽Wγγ⩽185 GeV. The total cross section of two real photons is described by a Regge parametrisation. We observe a steeper rise with the two-photon centre-of-mass energy as compared to the hadron–hadron and the photon–proton cross sections. The data are also compared to the expectations of different theoretical models.
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.
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