Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV.
Production cross sections as a function of Q**2. The differential cross sections are corrected to the centre of each bin.
Production cross section for the two photon data as a function of Q**2.
Differential cross section for non-resonance and RHO0 RHO0 data corrected to the centre of each bin.
The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4/pb, collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4 % and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W-->hadrons) = 67.50 +- 0.42 (stat.) +- 0.30(syst.) %, in agreement with the Standard Model. Differential cross sections as a function of the W- production angle are also measured for the semi-leptonic channels qqev and qqmv.
Measured cross section for the process E+ E- --> LEPTON NU LEPTON NU.
Measured cross section for the process E+ E- --> QUARK QUARKBAR ELECTRON NEUTRINO.
Measured cross section for the process E+ E- --> QUARK QUARKBAR MUON NEUTRINO.
We report on a study of radiative Bhabha and quasi-real Compton scattering at centre-of-mass energies between 50 GeV and 170 GeV, and 20 GeV and 140 GeV, respectively, using the L3 detector at LEP. The analysis is based on data corresponding to an integrated luminosity of 232.2 pb −1 . A total of 2856 radiative Bhabha and 4641 Compton scattering events are collected. Total and differential cross sections for both reactions are presented and found to be in good agreement with QED expectations. Our measurement of Compton scattering at the highest energies obtained so far is used to derive exclusion limits on the coupling λ for the on-shell production of an excited electron e ★ decaying into a γ e pair in the mass range 20 GeV
Measured cross sections for radiative Bhabha scattering events.
Measured cross sections for the quasi-real Compton scattering events.
The real part of the forward amplitude for Compton scattering on protons was measured through the interference between the Compton and Bethe-Heithler amplitudes by detecting the zero-degree electron pairs asymmetrically. The measurement was made at an average photon energy of 〈k〉=2.2 GeV, and an average momentum transfer to the recoil proton 〈t〉=−0.027 (GeV/c)2. The result confirms the prediction of the Kramers-Kronig relation.
No description provided.
Compton scattering of quasi-real virtual photons, gamma e+- -> gamma e+-, is studied with 0.6fb-1 of data collected by the L3 detector at the LEP e+e- collider at centre-of-mass energies root(s')=189-209GeV. About 4500 events produced by the interaction of virtual photons emitted by e+- of one beam with e-+ of the opposite beam are collected for effective centre-of-mass energies of the photon-electron and photon-positron systems in the range from root(s')= 35GeV up to root(s')=175GeV, the highest energy at which Compton scattering was ever probed. The cross sections of the gamma e+- -> gamma e+- process as a function of root(s') and of the rest-frame scattering angle are measured, combined with previous L3 measurements down to root(s')~20GeV, and found to agree with the QED expectations.
Measured Compton scattering cross section as a function of the effective centre of mass of the photon-electron system. THETA(RF=CM) is the electron rest frame scattering angle.
The measured angular distribution over the photon-electron centre of mass energy range 35 to 175 GeV.
The measured Compton scattering cross section using the full data sample including the lower energy data from Acciarri et al. PL B439(1998)183. Errors are combined statistics and systematics.
We measured the elastic scattering of αα at s = 126 GeV and of α p at s = 89 GeV . For αα , the differential cross section d σ /d t has a diffractive pattern minima at | t | = 0.10 and 0.38 GeV 2 . At small | t | = 0.05−0.07 GeV 2 , this cross section behaves like exp[(100 ± 10) t ]. Extrapolating a fit to the data to the optical point, we obtained for the total cross section α tot ( αα ) = 250 ± 50 mb and an integrated elastic cross section σ e1 ( αα ) = 45 ± mb. Another method of estimating σ tot ( αα ), based on measuring the interaction rate, yielded 295 ± 40 mb. For α p, d σ /d t has aminimum at | t | = 0.20 GeV 2 , and for 0.05 < | t | < 0.18 GeV 2 behaves like exp[(41 ± 2) t ]. Extrapolating this slope to | t | = 0, we found σ tot ( α p) = 130 ± 20 and σ e1 ( α p) = 20 ± 4mb. Results on pp elastic scattering at s = 63 GeV agree with previous ISR experiments.
Axis error includes +- 15/15 contribution.
Axis error includes +- 15/15 contribution.
METHOD 1 FOR SIG IS USING OPTICAL THEOREM. METHOD 2 FOR SIG IS BASED ON THE MEASURED LUMINOSITY-MONITOR CROSS SECTIONS.
By combining results from the MARK-J at PETRA on Bhabha scattering, μ + μ - and τ + τ - production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g V and g A in the framework of electroweak models containing a single Z 0 . In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin 2 θ W =0.24±0.11.
No description provided.
No description provided.
No description provided.
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.
Bhabha scattering data recorded at \sqrt{s}=189 GeV by the L3 detector at LEP are used to measure the running of the effective fine-structure constant for spacelike momentum transfers. The results are alpha^-1(-2.1 GeV^2) - alpha^-1(-6.25 GeV^2) = 0.78 +/- 0.26 alpha^-1(-12.25 GeV^2) - alpha^-1(-3434 GeV^2) = 3.80 +/- 1.29, in agreement with theoretical predictions.
No description provided.
Results extracted from the small angle Bhabha scattering sample at Z peak. Results contained total experimental uncertainty.
Results extracted from the large angle Bhabha scattering sample at sqrt(s) = 189 GeV. Results contained total experimental and theoretical uncertainty.
We have performed a high-statistics measurement of Bhabha scattering and of the production of hadrons in electron-positron annihilation at PETRA energies (12 GeV<~s<~36.7 GeV). Combining the results with measurements of μ+μ− and τ+τ− production enables us to compare our results with electroweak theory. We find sin2θw=0.27±0.08. This is in good agreement with the value obtained from neutrino experiments which were carried out in entirely different kinematic regions.
No description provided.
No description provided.
ASYMMETRY WAS USED.
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