Search For 3rd Generation Vector Leptoquarks In The Di Tau Di Jet Channel In Proton Antiproton Collisions At Square Root S

We search for third generation vector leptoquarks (V LQ3) produced in colliding p{bar p} beams operating at {radical}s = 1.96 TeV at the CDF experiment in Run II of the Fermilab Tevatron. We use 322 pb{sup -1} of data to search for the V LQ3 signal in the di-tau plus di-jet channel. For the first time, the full matrix element is used in the Monte Carlo simulation of this signal. With no events observed in the signal region, we set a 95% C.L. upper limit on the V LQ3 pair production cross section of {sigma} 344fb, assuming Yang-Mills couplings and Br(V LQ3 {yields} b{tau}) = 1, and a lower limit on the V LQ3 mass of m{sub V LQ3} 317 GeV=c{sup 2}. If theoretical uncertainties on the cross section are applied in the least favorable manner the results are {sigma} 360fb and m{sub V LQ3} 294 GeV=c{sup 2}. The Minimal coupling V LQ3 result is an upper limit on the cross section of {sigma} 493fb ({sigma} 610fb) and the lower limit on the mass is m{sub V LQ3} 251 GeV=c{sup 2} (m{sub V LQ3} 223 GeV=c{sup 2}) for the nominal (1{sigma} varied) theoretical expectation.

We search for third generation vector leptoquarks (V LQ3) produced in colliding p$ar{p}$ beams operating at √s = 1.96 TeV at the CDF experiment in Run II of the Fermilab Tevatron. We use 322 pb-1 of data to search for the V LQ3 signal in the di-tau plus di-jet channel. For the first time, the full matrix element is used in the Monte Carlo simulation of this signal. With no events observed in the signal region, we set a 95% C.L. upper limit on the V LQ3 pair production cross section of ? 344fb, assuming Yang-Mills couplings and Br(V LQ3 → b?) = 1, and a lower limit on the V LQ3 mass of msubV LQ3/sub 317 GeV=c2. If theoretical uncertainties on the cross section are applied in the least favorable manner the results are ? 360fb and msubV LQ3/sub 294 GeV=c2. The Minimal coupling V LQ3 result is an upper limit on the cross section of ? 493fb (? 610fb) and the lower limit on the mass is msubV LQ3/sub 251 GeV=csup2/sup (msubV LQ3/sub 223 GeV=c2) for the nominal (1? varied) theoretical expectation.

The CDF experiment has searched for production of a third generation vector leptoquark (VLQ3) in the di-tau plus di-jet channel using 322 pb−1 of Run II data. We review the production and decay theory and describe the VLQ3 model we have used as a benchmark. We study the analysis, including the data sample, triggers, particle identification, and event selection. We also discuss background estimates and systematic uncertainties. We have found no evidence for VLQ3 production and have set a 95% C.L. upper limit on the pair production cross section [sigma] to 344 fb, and exclude VLQ3 in the mass range m{sub VLQ3}> 317 GeV/c2, assuming Yang-Mills couplings and Br(LQ3 2!b[tau]) = 1. If theoretical uncertainties on the cross section are taken into account, the results are [sigma] 353 fb and m{sub VLQ3} 303 GeV/c2. For a VLQ3 with Minimal couplings, the upper limit on the cross section is [sigma] 493 fb ([sigma] 554 fb) and the lower limit on the mass is m{sub VLQ3} 251 GeV/c2 (m{sub VLQ3} 235 GeV/c2) for the nominal (1[sigma] varied) theoretical expectation.

A search for pair production of third-generation scalar leptoquarks decaying to top quark and $\tau$ lepton pairs is presented using proton-proton collision data at a center-of-mass energy of $\sqrt{s}$ = 8 TeV collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 fb-1. The search is performed using events that contain an electron or a muon, a hadronically decaying $\tau$ lepton, and two or more jets. The observations are found to be consistent with the standard model predictions. Assuming that all leptoquarks decay to a top quark and a $\tau$ lepton, the existence of pair produced, charge -1/3, third-generation leptoquarks up to a mass of 685 GeV is excluded at 95% confidence level. This result constitutes the first direct limit for leptoquarks decaying into a top quark and a $\tau$ lepton, and may also be applied directly to the pair production of bottom squarks decaying predominantly via the R-parity violating coupling [lambda]' 333.

A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying tau lepton, and at least two jets, using a $\sqrt{s}$=13 TeV pp collision data sample corresponding to an integrated luminosity of 12.9 inverse femtobarns collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and beta squared where beta is the branching fraction of leptoquark decay to a tau lepton and a bottom quark. Assuming beta=1, third-generation leptoquarks with masses below 850 GeV are excluded at 95 % confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, N[R], and right-handed W bosons, W[R], arising in a left-right symmetric extension of the standard model. In this search, W[R] bosons are assumed to decay to a tau lepton and N[R] followed by the decay of the N[R] to a tau lepton and an off-shell W[R] boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, W[R] boson masses below 2.9 TeV are excluded at 95 % confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with tau leptons in the final state.

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.