Recherche d'événements contenant un lepton isolé et de l'impulsion transverse manquante sur le collisionneur HERA avec le détecteur H1

Abstract : Events with an isolated lepton and missing transverse momentum have been observed in the 1994-1997 data of the H1 detector (37 pb-1) installed on the electron-proton HERA collider. This topology corresponds in the Standard Model to the production of a W or Z boson but the observed events contain a high hadronic transverse momentum which is unlikely within this interpretation.
This thesis describes the search for events with this topology, extending the phase space to low missing transverse momentum and including the complete HERA-1 data sample (118.3 pb-1) in order to improve the signal sensitivity and the statistical precision. Results show the persistence of an excess of events with a high hadronic transverse momentum. The hadronic channel of the W decay does not show any data excess but its sensitivity to the signal is not sufficient to contradict the observed excess in leptonic channel.
A possible interpretation of this excess beyond the Standard Model is the anomalous production of a top quark. The search for this process has been performed in this thesis using a classical cut-based analysis and a likelihood multi-variate analysis. Results are similar for both methods and show that some of the observed candidates are compatible with the anomalous production of a top quark. The top search in the hadronic channel does not show any data excess, but the lower signal sensitivity does not discard the top interpretation of the leptonic excess.
The statistical precision of the observed excess is not sufficient to conclude on the presence of New Physics and limits on the anomalous t u gamma coupling have been derived.
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Submitted on : Friday, July 25, 2003 - 2:53:24 PM
Last modification on : Thursday, January 18, 2018 - 1:55:10 AM
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Mireille Schneider. Recherche d'événements contenant un lepton isolé et de l'impulsion transverse manquante sur le collisionneur HERA avec le détecteur H1. Physique des Hautes Energies - Expérience [hep-ex]. Université Louis Pasteur - Strasbourg I, 2003. Français. ⟨tel-00003176⟩

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