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Title: Search for Admixture of Scalar Top in the t$$\bar{t}$$ Lepton+Jets Final State at √s= 1.96 TeV

Abstract

A search for pair production of scalar top (stop) quarks has been performed in the lepton+jets channel in ~ 1 fb -1 of data at the D0 experiment. Kinematic differences between $$\bar{t}$$ 1$$\tilde{t}$$ 1 and the dominant t$$\bar{t}$$ process are used to separate the two reactions. For stop-quark masses of 145-175 GeV, and chargino masses of 105-135 GeV, to which the stop quarks decay ($$\tilde{t}$$ 1 → $$\tilde{X}$$ 1 +b), we obtain upper limits on the $$\tilde{t}$$ 1$$\bar{t}$$ 1 cross section at 95% confidence, that are a factor of ~ 7-12 larger than expected from the Minimal Supersymmetric Standard Model (MSSM), as calculated in a next-to-leading-order (NLO) approximation in quantum chromodynamics (QCD).

Authors:
 [1]
  1. Univ. of Rochester, NY (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
921978
Report Number(s):
FERMILAB-THESIS-2007-45
TRN: US0801048
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; APPROXIMATIONS; CROSS SECTIONS; DECAY; PAIR PRODUCTION; QUANTUM CHROMODYNAMICS; QUARKS; SCALARS; STANDARD MODEL; Experiment-HEP

Citation Formats

Park, Su-Jung. Search for Admixture of Scalar Top in the t$\bar{t}$ Lepton+Jets Final State at √s= 1.96 TeV. United States: N. p., 2007. Web. doi:10.2172/921978.
Park, Su-Jung. Search for Admixture of Scalar Top in the t$\bar{t}$ Lepton+Jets Final State at √s= 1.96 TeV. United States. doi:10.2172/921978.
Park, Su-Jung. Mon . "Search for Admixture of Scalar Top in the t$\bar{t}$ Lepton+Jets Final State at √s= 1.96 TeV". United States. doi:10.2172/921978. https://www.osti.gov/servlets/purl/921978.
@article{osti_921978,
title = {Search for Admixture of Scalar Top in the t$\bar{t}$ Lepton+Jets Final State at √s= 1.96 TeV},
author = {Park, Su-Jung},
abstractNote = {A search for pair production of scalar top (stop) quarks has been performed in the lepton+jets channel in ~ 1 fb-1 of data at the D0 experiment. Kinematic differences between $\bar{t}$1$\tilde{t}$1 and the dominant t$\bar{t}$ process are used to separate the two reactions. For stop-quark masses of 145-175 GeV, and chargino masses of 105-135 GeV, to which the stop quarks decay ($\tilde{t}$1 → $\tilde{X}$1+b), we obtain upper limits on the $\tilde{t}$1$\bar{t}$1 cross section at 95% confidence, that are a factor of ~ 7-12 larger than expected from the Minimal Supersymmetric Standard Model (MSSM), as calculated in a next-to-leading-order (NLO) approximation in quantum chromodynamics (QCD).},
doi = {10.2172/921978},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Thesis/Dissertation:
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  • A search for pair production of the lightest supersymmetric partner of the top quark, {tilde t}{sub 1}, is performed in the lepton+jets channel using 0.9 fb{sup -1} of data collected by the D0 experiment. Kinematic differences between {tilde t}{sub 1}{bar {tilde t}}{sub 1} and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ({tilde t}{sub 1} {yields} {tilde {chi}}{sub 1}{sup +} b) are obtained for scalar top quark masses of 130-190 GeVmore » and chargino masses of 90-150 GeV.« less
  • I present the results of a search for pair production of scalar top quarks (more » $$\tilde{t}$$ 1) in an R-parity violating supersymmetric scenario using 322 pb -1 of p{bar p} collisions at √s = 1.96 TeV collected by the upgraded Collider Detector at Fermilab. I assume each $$\tilde{t}$$ 1 decays into a {tau} lepton and a b quark, with branching ratio {beta}, and search for final states containing either an electron or a muon from a leptonic τ decay, a hadronically decaying τ lepton, and two or more jets. Two candidate events pass my final selection criteria, consistent with the expectation from standard model processes. I present upper limits on the cross section times branching ratio squared σ($$\tilde{t}$$ 1$$\tilde{t}$$ 1) x β 2 as a function of the stop mass m($$\tilde{t}$$ 1). Assuming β = 1, I set a 95% confidence level limit m($$\tilde{t}$$ 1) > 153 GeV=c 2. These limits are also fully applicable to the case of a pair produced third generation scalar leptoquark that decays into a τ lepton and a b quark.« less
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  • We present a measurement of the single top quark cross section in the lepton plus jets final state using an integrated luminosity corresponding to 7.5 fb -1 of p\bar p collision data collected by the Collider Detector at Fermilab. The single top candidate events are identified by the signature of a charged lepton, large missing transverse energy, and two or three jets with at least one of them identified as originating from a bottom quark. A new Monte Carlo generator POWHEG is used to model the single top quark production processes, which include s-channel, t-channel, and Wt-channel. A neural network multivariate method is exploited to discriminate the single top quark signal from the comparatively large backgrounds. We measure a single top production cross section ofmore » $$3.04^{+0.57}_{-0.53} (\mathrm{stat.~+~syst.})$$ pb assuming $$m_{\rm top}=172.5$$~GeV/$c^2$. In addition, we extract the CKM matrix element value $$|V_{tb}|=0.96\pm 0.09~(\mathrm{stat.~+~syst.})\ ± 0.05~(\mathrm{theory})$$ and set a lower limit of $$|V_{tb}|>0.78$$ at the 95% credibility level.« less
  • We present the results of three analyses; amore » $WZ$ production cross section measurement, a search for new physics in anomalous top quark decays, and the search for the standard model Higgs boson, all with final states of three or more leptons -- either electrons or muons -- plus an imbalance of transverse momentum using Tevatron proton and anti-proton collisions at a center--of--mass energy of $$\sqrt{s}$$ = 1.96 TeV with the D0 detector at the Fermi National Accelerator Laboratory in Chicago, IL. The first analysis reports a measurement of the $$WZ \rightarrow \ell^{\prime}\nu\ell\bar{\ell}$$ cross section. Using 4.1 $$fb^{-1}$$ of integrated luminosity, we measure a cross section of 3.90$$_{-0.85}^{+1.01}$$($stat+syst$) $$\pm$$ 0.31($lumi$) pb, which is found to be in good agreement with the standard model prediction. The second analysis is an extension of the first, in which we use the same dataset and look for the flavor changing neutral current decay of $$t \rightarrow Zq$$ in $$p\bar {p} \rightarrow t\bar{t} \rightarrow WbZq \rightarrow \ell^{\prime}\nu\ell\bar{\ell} + \rm{jets}$$ decays. Here $q$ is considered to be either a $u$ or $c$ quark, and both the $q$ and $b$ quarks decay hadronically. We find no evidence of flavor changing neutral current production and set upper limits on the branching ratio of $$BR(t \rightarrow Zq) < 3.2\%$$ observed, with an expected limit of $$< 3.8\%$$, at the 95\% confidence level. Finally, we present a search for the standard model Higgs boson, using associated $WH$ and $ZH$ production, in the $$ee\mu$$ final state. Now using 9.7 $$fb^{-1}$$, the full dataset available at D0, we observe no excess above the standard model background prediction and extract limits on the Higgs boson production cross section times branching ratio for a Higgs boson mass range of $$m_{H}$$ = 100 -- 200 GeV/c$^2$, in intervals of 5 GeV/c$^2$.« less