This document describes the search for second-generation leptoquarks (LQ{sub 2}) in around 114pb{sup -1} of p{bar p} collisions, recorded with the D0 detector between September 2002 and June 2003 at a centre-of-mass energy of {radical}s = 1.96TeV. The predictions of the Standard Model and models including scalar leptoquark production are compared to the data for various kinematic distributions. Since no excess of data over the Standard Model prediction has been observed, a lower limit on the leptoquark mass of M{sub LQ{sub 2}}{sup {beta}=1}> 200GeV has been calculated at 95% confidence level (C.L.), assuming a branching fraction of {beta} = BF(LQ{sub 2} {yields} {mu}j) = 100% into a charged lepton and a quark. The corresponding limit for {beta} = 1/2 is M{sub LQ{sub 2}}{sup {beta}=1/2}> 152 GeV. Finally, the results were combined with those from the search in the same channel at D0 Run I. This combination yields the exclusion limit of M{sub LQ{sub 2}}{sup {beta}=1}> 222 GeV (177GeV) for (beta) = 1 (1/2) at 95% C.L., which is the best exclusion limit for scalar second-generation leptoquarks (for {beta} = 1) from a single experiment to date.

In the study presented in this document, about 114 pb[sup -1] of p[bar p] collisions from Run II, collected with the D0 detector between September 2002 and June 2003, are compared to Standard-Model predictions and predictions from models including scalar second-generation leptoquarks. since no deviation from the Standard Model is observed, upper limits on the leptoquark cross-section are calculated and translated into lower bounds to the mass of scalar leptoquarks. Consequently, the results are combined with earlier results from D0 Run I in the same channel.

Our search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb-1, were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for [beta] = 1.0 (0.5), where b is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, secondgeneration scalar leptoquarks with masses less than 1080 (760) GeV are excluded for [beta] = 1.0 (0.5). Furthermore, mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of leptoquarks and RPV top squarks to date.

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.