Browsing by Author "Espirito Santo, M.C."
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- Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEPPublication . ALEPH, DELPHI, L3, OPAL, LEP Electroweak collaboration (1644 authors); David, A.; Abreu, P.; Andringa, S.; Anjos, N.; Castro, N.; De Angelis, A.; Espirito Santo, M.C.; Goncalves, P.; Onofre, A.; Pimenta, M.; Tome, B.; Veloso, F.Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb$^{-1}$ collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, $M_W$ and $\Gamma_W$, the branching fraction of W decays to hadrons, $B(W\to\mathrm{had})$, and the trilinear gauge-boson self-couplings $g^Z_1$, $\kappa_\gamma$ and $\lambda_\gamma$ are determined to be: M_W = 80.376 \pm 0.033 ~GeV \Gamma_W = 2.195 \pm 0.083 ~GeV B(W\to\mathrm{had}) = 67.41 \pm 0.27 % g^Z_1 = 0.984 ^{+0.018}_{-0.020} \kappa_\gamma = 0.982 \pm 0.042 \lambda_\gamma = -0.022 \pm 0.019
- Measurement of the electron structure function F$\frac{e}{2}$ at LEP energiesPublication . DELPHI collaboration (343 authors); Abreu, P.; Andringa, S.; Anjos, N.; Castro, N.; De Angelis, A.; Espirito Santo, M.C.; Gonçalves, P.; Onofre, A.; Peralta, L.; Pimenta, M.; Tomé, B.; Veloso, F.The hadronic part of the electron structure function F2e has been measured for the first time, using e+e− data collected by the DELPHI experiment at LEP, at centre-of-mass energies of s=91.2–209.5 GeV . The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function F2e data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function F2γ analyses and help in refining existing parameterisations.
- Search for Charged Higgs bosons: Combined Results Using LEP DataPublication . ALEPH, DELPHI, L3, OPAL, LEP collaboration (1216 authors); Abreu, P.; Andringa, S.; Anjos, N.; Castro, Nuno Filipe; De Angelis, A.; Espirito Santo, M.C.; Goncalves, P.; Onofre, A.; Peralta, L.; Pimenta, M.; Tome, B.; Veloso, F.; David, A.The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for pair-produced charged Higgs bosons in the framework of Two Higgs Doublet Models (2HDMs). The data of the four experiments are statistically combined. The results are interpreted within the 2HDM for Type I and Type II benchmark scenarios. No statistically significant excess has been observed when compared to the Standard Model background prediction, and the combined LEP data exclude large regions of the model parameter space. Charged Higgs bosons with mass below 80 GeV/c^2 (Type II scenario) or 72.5 GeV/c^2 (Type I scenario, for pseudo-scalar masses above 12 GeV/c^2) are excluded at the 95% confidence level.