Search for Pair Production of First-generation Leptoquarks in P Pbar Collisions at Sqrt(s)

Search for Pair Production of First-generation Leptoquarks in P Pbar Collisions at Sqrt(s)
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Total Pages: 10
Release: 2009
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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.

Search for Pair Production of First and Second Generation Leptoquarks in Proton-proton Collisions at $\sqrt{s}

Search for Pair Production of First and Second Generation Leptoquarks in Proton-proton Collisions at $\sqrt{s}
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Total Pages: 48
Release: 2015
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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.

Search for First Generation Scalar Leptoquarks in the Evjj Channel in Pp Collisions at Sqrt(s)

Search for First Generation Scalar Leptoquarks in the Evjj Channel in Pp Collisions at Sqrt(s)
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Total Pages: 29
Release: 2011
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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.

Search for Pair Production of Second Generation Scalar Leptoquarks in Ppbar Collisions at the Tevatron

Search for Pair Production of Second Generation Scalar Leptoquarks in Ppbar Collisions at the Tevatron
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Total Pages: 126
Release: 2008
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As predicted by numerous extensions of the Standard Model, leptoquarks (LQ) are hypothetical bosons allowing lepton-quark transitions. Under the assumption that they couple only to quarks and leptons of the same generation, three generations of leptoquarks can be distinguished. The search for the pair production of second generation scalar leptoquarks has been carried out in p{bar p} collisions at √s = 1.96TeV, using an integrated luminosity of 1 fb−1 collected by the D0 experiment at the Tevatron collider between August 2002 and February 2006. Topologies arising from the LQ{ovr LQ} → [mu]q[nu]q and LQ{ovr LQ} → [mu]q[mu]q decay modes have been investigated. In order to maximize the available statistics, a method for the combination of various prescaled triggers with an inclusive OR has been developed. Since no excess of data over the Standard Model prediction has been observed, upper limits on the leptoquark pair production cross section have been derived at 95% confidence level as function of the leptoquark mass and the branching fraction [beta] = Br(LQ → [mu]q), and are interpreted as lower limits on the leptoquark mass as function of [beta]. For [beta] = 1, [beta] = 1/2 and [beta] = 0.1, the combination of the two channels excludes scalar second generation leptoquarks with masses up to 309GeV, 262GeV, and 174GeV, respectively. The lower bounds on the scalar second generation leptoquark mass obtained for [beta] ≥ 0.1 are the best exclusion limits to date.

Search for First-generation Scalar Leptoquarks in P Anti-p Collisions at S**(1/2)

Search for First-generation Scalar Leptoquarks in P Anti-p Collisions at S**(1/2)
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Total Pages: 8
Release: 2005
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We report on a search for pair production of first-generation scalar leptoquarks (LQ) in pp collisions at √(s)=1.96 TeV using an integrated luminosity of 203 pb−1 collected at the Fermilab Tevatron collider by the CDF experiment. We observe no evidence for LQ production in the topologies arising from LQLQ→eqeq and LQLQ→eq?q, and derive 95% C.L. upper limits on the LQ production cross section. The results are combined with those obtained from a separately reported CDF search in the topology arising from LQLQ→?q?q and 95% C.L. lower limits on the LQ mass as a function of ?=BR(LQ→eq) are derived. The limits are 236, 205 and 145 GeV/c2 for ?=1, ?=0.5 and ?=0.1, respectively.

Search for First Generation Leptoquark Pair Production in the Electron + Missing Energy + Jets Final State

Search for First Generation Leptoquark Pair Production in the Electron + Missing Energy + Jets Final State
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Total Pages: 7
Release: 2011
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We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb−1 collected with the D0 detector at the Fermilab Tevatron Collider in p{bar p} collisions at √s = 1.96 TeV. In the channel LQ{ovr LQ} → eq[nu]{sub e}q', where q,q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C.L. lower limit of 326 GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays to eq and [nu]{sub e}q'.