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Title: Direct Searches for 3rd Generation Scalar Leptoquarks at the Run II Tevatron


This dissertation reports on a search for scalar Leptoquarks (LQ) decaying into third generation leptons and quarks.

  1. Tufts Univ., Medford, MA (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
Report Number(s):
UMI-32-58323; FERMILAB-THESIS-2007-91
DOE Contract Number:
Resource Type:
Country of Publication:
United States

Citation Formats

Sun, Hao. Direct Searches for 3rd Generation Scalar Leptoquarks at the Run II Tevatron. United States: N. p., 2007. Web. doi:10.2172/1402434.
Sun, Hao. Direct Searches for 3rd Generation Scalar Leptoquarks at the Run II Tevatron. United States. doi:10.2172/1402434.
Sun, Hao. Mon . "Direct Searches for 3rd Generation Scalar Leptoquarks at the Run II Tevatron". United States. doi:10.2172/1402434.
title = {Direct Searches for 3rd Generation Scalar Leptoquarks at the Run II Tevatron},
author = {Sun, Hao},
abstractNote = {This dissertation reports on a search for scalar Leptoquarks (LQ) decaying into third generation leptons and quarks.},
doi = {10.2172/1402434},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}

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  • This dissertation sets new limits on the mass of the scalar leptoquark from direct searches carried out at the Run II CDF detector using data from March 2001 to October 2003. The data analyzed has a total time-integrated measured luminosity of 198 pb -1 of pmore » $$\bar{p}$$ collisions with √s = 1.96 TeV. Leptoquarks are assumed to be pair-produced and to decay into a lepton and a quark of the same generation. They consider two possible leptoquark decays: (1) β = BR(LQ → μq) = 1.0, and (2) β = BR(LQ → μq) = 0.5. For the β = 1 channel, they focus on the signature represented by two isolated high-p T muons and two isolated high-p T jets. For the β = 1/2 channel, they focus on the signature represented by one isolated high-p T muon, large missing transverse energy, and two isolated high-p T jets. No leptoquark signal is experimentally detected for either signature. Using the next to leading order theoretical cross section for scalar leptoquark production in p$$\bar{p}$$ collisions [1], they set new mass limits on second generation scalar leptoquarks. They exclude the existence of second generation scalar leptoquarks with masses below 221(175) GeV/c 2 for the β = 1(1/2) channels.« less
  • 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 pmore » $$\bar{p}$$ 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$$\bar{LQ}$$ → μqvq and LQ$$\bar{LQ}$$ → μqμq 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 β = Br(LQ →μq), and are interpreted as lower limits on the leptoquark mass as function of β. For β = 1, β = 1/2 and β = 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 β ≥ 0.1 are the best exclusion limits to date.« less
  • We search for third generation vector leptoquarks (V LQ3) produced in colliding pmore » $$\bar{p}$$ 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 σ < 344fb, assuming Yang-Mills couplings and Br(V LQ3 → bτ) = 1, and a lower limit on the V LQ3 mass of m V LQ3 > 317 GeV=c 2. If theoretical uncertainties on the cross section are applied in the least favorable manner the results are σ < 360fb and m V LQ3 > 294 GeV=c 2. The Minimal coupling V LQ3 result is an upper limit on the cross section of σ < 493fb (σ < 610fb) and the lower limit on the mass is m V LQ3 > 251 GeV=c 2 (m V LQ3 > 223 GeV=c 2) for the nominal (1σ varied) theoretical expectation.« less
  • Leptoquarks (LQ) are particles with both color and lepton number predicted in some gauge theories and composite models. Current theory suggests that leptoquarks would come in three different generations. We report on a search for charge 1/3 third generation leptoquarks produced in pmore » $$\bar{p}$$ collisions at √s = 1.96 TeV using data collected by the D0 detector at Fermilab. Such leptoquarks would decay into a tau-neutrino plus a b-quark with branching fraction B. We present preliminary results on an analysis where both leptoquarks decay into neutrinos giving a final state with missing energy and two b-jets. Using 425(recorded) pb -1 of data, we place limits on σ(p$$\bar{p}$$ → LQ$$\bar{LQ}$$)B 2 as a function of the leptoquark mass. Assuming B = 1, we excluded at the 95% confidence level scalar third generation leptoquarks with M LQ < 219 GeV.« less
  • A search for first generation scalar leptoquarks was done at the DO detector at Fermi National Accelerator Laboratory from 15 pb -1 of data taken during the 1992--1993 colder run. At Fermilab`s pmore » $$\bar{p}$$ collider with a center-of-mass energy of 1.8 TeV, leptoquarks are produced mostly by the strong force in pairs. Leptoquarks carry fractional charge, color, and also lepton and baryon quantum numbers. First generation leptoquarks couple exclusively to the electron, electron neutrino, and the u and d quarks; such a leptoquark would decay into, for example, an electron plus a quark. Signatures for leptoquarks at p$$\bar{p}$$ colliders that have been investigated at DO are two electrons plus two jets and one electron plus missing energy (from an electron neutrino) plus two jets.« less