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Title: Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees

Abstract

The top quark produced through the electroweak channel provides a direct measurement of the V tb element in the CKM matrix which can be viewed as a transition rate of a top quark to a bottom quark. This production channel of top quark is also sensitive to different theories beyond the Standard Model such as heavy charged gauged bosons termed W'. This thesis measures the cross section of the electroweak produced top quark using a technique based on using the matrix elements of the processes under consideration. The technique is applied to 2.3 fb -1 of data from the D0 detector. From a comparison of the matrix element discriminants between data and the signal and background model using Bayesian statistics, we measure the cross section of the top quark produced through the electroweak mechanism σ(p$$\bar{p}$$ → tb + X, tqb + X) = 4.30 -1.20 +0.98 pb. The measured result corresponds to a 4.9σ Gaussian-equivalent significance. By combining this analysis with other analyses based on the Bayesian Neural Network (BNN) and Boosted Decision Tree (BDT) method, the measured cross section is 3.94 ± 0.88 pb with a significance of 5.0σ, resulting in the discovery of electroweak produced top quarks. Using this measured cross section and constraining |V tb| < 1, the 95% confidence level (C.L.) lower limit is |V tb| > 0.78. Additionally, a search is made for the production of W' using the same samples from the electroweak produced top quark. An analysis based on the BDT method is used to separate the signal from expected backgrounds. No significant excess is found and 95% C.L. upper limits on the production cross section are set for W' with masses within 600-950 GeV. For four general models of W{prime} boson production using decay channel W' → t$$\bar{p}$$, the lower mass limits are the following: M(W' L with SM couplings) > 840 GeV; M(W' R) > 880 GeV or 890 GeV if the right-handed neutrino is lighter or heavier than W{prime}{sub R}; and M(W' L+R) > 915 GeV.

Authors:
 [1]
  1. Brown Univ., Providence, RI (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
973216
Report Number(s):
FERMILAB-THESIS-2010-02
TRN: US1001713
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BOSONS; CROSS SECTIONS; DECAY; MATRIX ELEMENTS; NEURAL NETWORKS; NEUTRINOS; PRODUCTION; STANDARD MODEL; STATISTICS; T QUARKS; DECISION TREE ANALYSIS; Experiment-HEP

Citation Formats

Pangilinan, Monica. Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees. United States: N. p., 2010. Web. doi:10.2172/973216.
Pangilinan, Monica. Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees. United States. doi:10.2172/973216.
Pangilinan, Monica. Sat . "Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees". United States. doi:10.2172/973216. https://www.osti.gov/servlets/purl/973216.
@article{osti_973216,
title = {Top Quark Produced Through the Electroweak Force: Discovery Using the Matrix Element Analysis and Search for Heavy Gauge Bosons Using Boosted Decision Trees},
author = {Pangilinan, Monica},
abstractNote = {The top quark produced through the electroweak channel provides a direct measurement of the Vtb element in the CKM matrix which can be viewed as a transition rate of a top quark to a bottom quark. This production channel of top quark is also sensitive to different theories beyond the Standard Model such as heavy charged gauged bosons termed W'. This thesis measures the cross section of the electroweak produced top quark using a technique based on using the matrix elements of the processes under consideration. The technique is applied to 2.3 fb-1 of data from the D0 detector. From a comparison of the matrix element discriminants between data and the signal and background model using Bayesian statistics, we measure the cross section of the top quark produced through the electroweak mechanism σ(p$\bar{p}$ → tb + X, tqb + X) = 4.30-1.20+0.98 pb. The measured result corresponds to a 4.9σ Gaussian-equivalent significance. By combining this analysis with other analyses based on the Bayesian Neural Network (BNN) and Boosted Decision Tree (BDT) method, the measured cross section is 3.94 ± 0.88 pb with a significance of 5.0σ, resulting in the discovery of electroweak produced top quarks. Using this measured cross section and constraining |Vtb| < 1, the 95% confidence level (C.L.) lower limit is |Vtb| > 0.78. Additionally, a search is made for the production of W' using the same samples from the electroweak produced top quark. An analysis based on the BDT method is used to separate the signal from expected backgrounds. No significant excess is found and 95% C.L. upper limits on the production cross section are set for W' with masses within 600-950 GeV. For four general models of W{prime} boson production using decay channel W' → t$\bar{p}$, the lower mass limits are the following: M(W'L with SM couplings) > 840 GeV; M(W'R) > 880 GeV or 890 GeV if the right-handed neutrino is lighter or heavier than W{prime}{sub R}; and M(W'L+R) > 915 GeV.},
doi = {10.2172/973216},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat May 01 00:00:00 EDT 2010},
month = {Sat May 01 00:00:00 EDT 2010}
}

Thesis/Dissertation:
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