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Mesures des sections efficaces et des asymétries difermioniques avec le détecteur Aleph à LEP2 - Interprétations au-delà du Modèle Standard

Abstract : During the second phase of LEP, e+e- collisions were recorded at
center-of mass energies ranging between 130 GeV and 189 GeV. The complete statistics accumulated at these points allows us to perform precise
tests of the Standard Model structure, beyond the Z-mass. It also provides a
large scope for direct and indirect searches of new physics phenomena.

The present work is based on the selection of e+e- -> ff events taken with the Aleph detector from 1995 to 1998, for an integrated luminosity of 500 pb-1. In a first part we present the selection of dimuon, di-tau, di-electron events that have been developped for this study. The hadronic selection used in Aleph is also detailled in a devoted part. In each case, the estimation of systematic uncertainties is described. They are on the same level of accuracy than the statistical errors, found to range between 0.6% (di-electron) and 3.5% (dimuon).

From these selections we derive the di-fermionic cross-sections as well
as the asymmetries computed for the di-lepton channels. Measurements are
found to be in reasonable agreement with the Standard Model expectations.

Cross-sections and asymmetries are sensitive to the presence of possible
new physics. In particular, any deviations may be interpreted either as the
presence of new interactions via contact-terms, or as the presence of extra
particles interacting with matter. On contrary, if no significant deviation
is actually seen in our data, we then can set lower bounds to the scale of
new physics, or to the mass of such extra-particles.
In this document we use the context of the 4-fermion contact interactions to
set limits on the energy scale of new physics. Such limits are found to
range between 7 and 15 GeV depending on the modelisation used. We also put lower limits on the mass of leptoquarks, 590 GeV/c^2 for vector leptoquarks and 710 GeV/c^2 for scalar leptoquarks. Eventually, we also present the limits derived in the context of R-parity violated supersymmetry, putting constraint on the s-neutrino mass. Our study excludes such particles below a few hundred GeV/c^2 mass for high values of their Yukawa couplings
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Contributor : Elsa Merle <>
Submitted on : Monday, March 11, 2002 - 12:58:56 PM
Last modification on : Friday, November 6, 2020 - 3:29:56 AM
Long-term archiving on: : Tuesday, September 11, 2012 - 5:05:14 PM


  • HAL Id : tel-00001205, version 1



Elsa Merle. Mesures des sections efficaces et des asymétries difermioniques avec le détecteur Aleph à LEP2 - Interprétations au-delà du Modèle Standard. Physique des Hautes Energies - Expérience [hep-ex]. Université de Savoie, 1999. Français. ⟨tel-00001205⟩



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