Contraintes du Modele standard par les mesures de sections efficaces et asymetries Z-->ffbar avec le detecteur ALEPH au LEP.

Abstract : This work is devoted to the precision tests of the electro-weak sector of the standard model via the determination of the Z-lineshape parameters $M_Z$, $\Gamma_Z$, $\sigma_{had}^0$ and $R_{had}$ extracted from the fermionic cross-sections measured on 89 to 94 data in Aleph. The first section reminds the formalism and the observables used to describe the Z-resonance physics. In a second step, the LEP collider is presented with the procedures used to determine the beam energy, this parameter being the main source of uncertainty in $M_Z$ and $\Gamma_Z$ determination. In the following part, the Aleph experimental context is decribed, together with the measurement of the luminosity from bhabhas counting. Then the hadronic cross section measurements are presented, emphasizing on the improvement performed on the systematic bias evaluation to the hadrons selection. This leads to a precision at the per mille level in cross-sections. Leptonic cross-sections measured in Aleph are also reported. The Z-resonance parameters are then derived. A great agreement is observed with the prediction of the standard model of the EW interactions. The interpretation of such measurements within this model leads to the determination of the number of light neutrinos species and to constraints on the top quark mass, compatible with direct measurements from Fermilab.
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High Energy Physics - Experiment. Université Claude Bernard - Lyon I, 1996. French


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Contributor : Arnaud Lucotte <>
Submitted on : Monday, March 10, 2003 - 2:23:59 PM
Last modification on : Monday, March 10, 2003 - 2:23:59 PM

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Arnaud LUCOTTE. Contraintes du Modele standard par les mesures de sections efficaces et asymetries Z-->ffbar avec le detecteur ALEPH au LEP.. High Energy Physics - Experiment. Université Claude Bernard - Lyon I, 1996. French. <tel-00002529>

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