Recherche du partenaire supersymetrique du quark Top et contribution a l'amelioration de la calorimetrie de l'experience DO pour la Phase II du Tevatron

Abstract : Supersymmetry could be the most natural extension of the Standard Model. In this thesis we present a new search for the sTop, the hypothetical scalar partner of the Top quark, that we performed in the framework of the Minimal Supersymmetric Standard Model (MSSM), using the Run I data of the DO experiment, which corresponds to an integrated luminosity of $108$ pb$^{-1}$. We selected events with one electron, one muon and missing transverse energy in the final state, which can be the decay product of pair of sTop quarks in $3$ ($\tilde{t} \rightarrow b l \tilde{\nu}$), or $4$-body ($\tilde{t} \rightarrow b \oa l {\nu_l}$). No signal is seen and the results are interpreted in terms of limits on the sTop production cross-section and exclusion regions in the parameter space ($m_{\tilde{t}},\moa$) or ($m_{\tilde{t}},\msnu$). This new type of selection at the Tevatron for the search of the sTop allowed us to put stronger constraints than those previously published at LEP or at the Tevatron in the $\tilde{t} \rightarrow b l \tilde{\nu}$ channel, and the first limits ever set in the $4$-body decay channel. For the $3$-body channel, assuming that the sneutrino is the lightest supersymmetric particle (LSP), the excluded region at $95\%$ confidence level extends up to a sTop mass of $142$ ($130$) GeV if the sneutrino mass ($\msnu$) is $43$ ($86$) GeV. If the $4$-body decay channel dominates, assuming that the neutralino is the LSP, the limit depends on the sneutrino mass. If it is light enough (${m_{\tilde{\nu}}} \ \lapprox\ 100$ GeV) this limit reaches a sTop mass of $132$ GeV for a neutralino mass of $60$ GeV. In all searches for new particles, the calorimetry plays a crucial role from the experimental point of view. The expected increase in integrated luminosity in the Run II which started on the $1^{st}$ of March $2001$, and the detector upgrade which has been achieved over the last three years will allow to extend these exclusion domains or to discover the sTop. We thus also describe in this thesis our contribution to the calorimeter upgrade, both on the on-line calibration system, and on the calorimeter reconstruction software.
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High Energy Physics - Experiment. Université Pierre et Marie Curie - Paris VI, 2001. French
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https://tel.archives-ouvertes.fr/tel-00001032
Contributor : Bob Olivier <>
Submitted on : Thursday, January 17, 2002 - 6:49:21 PM
Last modification on : Thursday, January 17, 2002 - 6:49:21 PM

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• HAL Id : tel-00001032, version 1

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Bob Olivier. Recherche du partenaire supersymetrique du quark Top et contribution a l'amelioration de la calorimetrie de l'experience DO pour la Phase II du Tevatron. High Energy Physics - Experiment. Université Pierre et Marie Curie - Paris VI, 2001. French. <tel-00001032>

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