We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies. The distributions of event shape variables and the energy dependence of their mean values are measured from 30GeV to 189GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbative component. We obtain a universal value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong coupling constant at each of the selected energies. The measurements demonstrate the running of alpha_s as expected in QCD with a value of alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).
Distribution for THRUST at c.m. energy 189 GeV.
Distribution for Heavy Jet Mass at c.m. energy 189 GeV.
Distribution for Total Jet Broadening at c.m. energy 189 GeV.
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.
Measured cross sections for the hadronic events.
Measured cross sections for the muon-pair events.
Measured cross sections for the tau-pair events.
The total and differential cross sections of the process e+e- -> n gamma with n >= 2 are measured using data collected by the L3 experiment at centre-of-mass energies of \sqrt{s}=183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.
Measured cross section.
Measured differential cross sections corrected for efficiency and additional photons as a function of cos(theta) where theta is the polar angle of the event defined as. cos(theta)=ABS((sin(theta1-theta2)/2)/(sin(theta1+theta2)/2)).
Inclusive production of $\mathrm{D^{*\pm}}$ mesons in two-photon collisions was measured by the L3 experiment at LEP. The data were collected at a centre-of-mass energy $\sqrt{s} = 189$ GeV with an integrated luminosity of $176.4 \mathrm{pb^{-1}}$. Differential cross sections of the process $\mathrm{e^+e^- \to D^{*\pm} X}$ are determined as functions of the transverse momentum and pseudorapidity of the $\mathrm{D^{*\pm}}$ mesons in the kinematic region 1 GeV $< p_{T}^{\mathrm{D^*}} < 5 $ GeV and $\mathrm{|\eta^{D^*}|} < 1.4$. The cross section integrated over this phase space domain is measured to be $132 \pm 22(stat.) \pm 26(syst.)$ pb. The differential cross sections are compared with next-to-leading order perturbative QCD calculations.
The measured cross sections, as a function of PT over the bin ranges and the differential cross sections after bin-centre corrections.
The measured cross sections, as a function of pseudorapidity over the bin ranges and the differential cross sections after bin-centre corrections.
Integrated cross section in the visible kinematic region.
The reaction e + e − → e + e − γ ∗ γ ∗ → e + e − hadrons is analysed using data collected by the L3 detector during the LEP runs at s = 130−140 GeV and s = 161 GeV . The cross sections σ(e + e − → e + e − hadrons) and σ(γγ → hadrons) are measured in the interval 5 ≤ W γγ ≤ 75 GeV. The energy dependence of the σ(γγ → hadrons) cross section is consistent with the universal Regge behaviour of total hadronic cross sections.
No description provided.
No description provided.
We have studied the process e<sup loc="post">+</sup>e<sup loc="post">−</sup> → nγ (n ≥ 2) at an average center-of-mass energy of 133 GeV using the L3 detector at LEP. For an integrated luminosity of 4.95 pb<sup loc="post">−1</sup> we find one γγγγ(γ) final state with only hard photons. The rates of both γγγ and γγ events are consistent with QED expectations. The cross section of the reaction e<sup loc="post">+</sup>e<sup loc="post">−</sup> → γγ(γ) in the polar range 16° < θγ < 164° is measured to be 22.6 ± 2.2 pb. Decays into photons of narrow scalar resonances with masses between 90 and 130 GeV are not observed. The observation of the event with four energetic photons is consistent with QED although the kinematic configuration of the photons is atypical.
Cross section for process E+ E- --> GAMMA GAMMA (GAMMA) with two hard photons.Error is purely statistical, systematic effects are neglected.
No description provided.
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