Le sujet de cette thèse est la recherche des leptoquarks scalaires et vectoriels de première génération produits en couple dans des collisions proton-antiproton à une énergie du centre de masse de 1.8 TeV et se désintégrant dans les canaux "e[nu]jj" et "eejj". L'analyse a été conduite sur les données récoltées par l'expérience CDF pendant la période 1992-1995.

Le sujet de cette thèse est la recherche des leptoquarks scalaires et vectoriels de première génération produits en couple dans des collisions proton-antiproton à une énergie du centre de masse de 1.8 TeV et se désintégrant dans les canaux "e[nu]jj" et "eejj". L'analyse a été conduite sur les données récoltées par l'expérience CDF pendant la période 1992-1995.

A search for pair production of first-generation leptoquarks (LQ) is performed with data collected by the D0 experiment in p{bar p} collisions at √s = 1.96 TeV at the Fermilab Tevatron Collider. In a sample of data corresponding to ≈ 1 fb−1 the search has been performed on the final states with two electrons and two jets or one electron, two jets and missing transverse energy. We find our data consistent with standard model expectations. The results are combined with those found in a previous analysis of events with two jets and missing transverse energy to obtain scalar LQ mass limits. We set 95% C.L. lower limits on a scalar LQ mass of 299 GeV, 284 GeV and 216 GeV for [beta] = 1, [beta] = 0.5 and [beta] = 0.02 respectively, where [beta] is the LQ branching ratio in the eq channel. This improves the results obtained with a lower luminosity sample from Run II of the Tevatron. Lower limits on vector LQ masses with different couplings from 357 GeV to 464 GeV for [beta] = 0.5 are also set using this analysis.

A search for pair-production of first generation scalar leptoquarks is performed in the final state containing an electron, a neutrino, and at least two jets using proton-proton collision data at sqrt(s)=7 TeV. The data were collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 36 inverse picobarns. The number of observed events is in good agreement with the predictions for standard model processes. Prior CMS results in the dielectron channel are combined with this electron+neutrino search. A 95% confidence level combined lower limit is set on the mass of a first generation scalar leptoquark at 340 GeV for beta=0.5, where beta is the branching fraction of the leptoquark to an electron and a quark. These results represent the most stringent direct limits to date for values of beta greater than 0.05.

We describe a search for first generation leptoquarks decaying into the eejj final state in $p\bar{p}$ collisions at a center of mass energy of 1.96 TeV using the D0 detector at the Fermilab Tevatron. this search is based on data collected during 2002-2003 with an integrated luminosity of (130.4 =- 8.5) pb -1. Leptoquarks are assumed to be produced in pairs and to decay into an electron and a quark with a branching ration ?. We observe no evidence for leptoquarks, and set an upper cross section limit of 0.086 pb at the 95% confidence level corresponding to a lower mass limit of 231 GeV/c2 for scalar leptoquarks when ? = 1.