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Title: Measurement of top quark polarization in top-antitop lepton+jets final states at DØ

Abstract

This thesis presents a measurement of the top quark polarization in the $$t\overline{t}$$ events produced in $$p\overline{p}$$ collisions at $$\sqrt{s}=1.96$$ TeV using data corresponding to 9.7 fb$$^{-1}$$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The final states used in the measurement contain one lepton and at least three jets. The polarization is measured using the angular distribution of leptons along three different axes: the beam axis, the helicity axis, and the transverse axis normal to the $$t\overline{t}$$ production plane. This is the first measurement of top quark polarization at the Tevatron Collider in lepton+jets final states, and the first measurement of transverse polarization in $$t\overline{t}$$ production. The polarization along the beam axis is combined with the previous result in the dilepton final states by the D0 experiment. The observed distributions are consistent with the Standard Model of nearly no polarization and no indication for beyond Standard Model physics is observed. The measurement offers legacy result from unique Tevatron Collider data and provides more information about the top quark production and decays, about the properties of the heaviest elementary particle.

Authors:
 [1]
  1. Czech Technical Univ., Prague (Czech Republic)
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:
1347928
Report Number(s):
FERMILAB-THESIS-2017-06
1518866
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Augsten, Kamil. Measurement of top quark polarization in top-antitop lepton+jets final states at DØ. United States: N. p., 2017. Web. doi:10.2172/1347928.
Augsten, Kamil. Measurement of top quark polarization in top-antitop lepton+jets final states at DØ. United States. doi:10.2172/1347928.
Augsten, Kamil. Sun . "Measurement of top quark polarization in top-antitop lepton+jets final states at DØ". United States. doi:10.2172/1347928. https://www.osti.gov/servlets/purl/1347928.
@article{osti_1347928,
title = {Measurement of top quark polarization in top-antitop lepton+jets final states at DØ},
author = {Augsten, Kamil},
abstractNote = {This thesis presents a measurement of the top quark polarization in the $t\overline{t}$ events produced in $p\overline{p}$ collisions at $\sqrt{s}=1.96$ TeV using data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The final states used in the measurement contain one lepton and at least three jets. The polarization is measured using the angular distribution of leptons along three different axes: the beam axis, the helicity axis, and the transverse axis normal to the $t\overline{t}$ production plane. This is the first measurement of top quark polarization at the Tevatron Collider in lepton+jets final states, and the first measurement of transverse polarization in $t\overline{t}$ production. The polarization along the beam axis is combined with the previous result in the dilepton final states by the D0 experiment. The observed distributions are consistent with the Standard Model of nearly no polarization and no indication for beyond Standard Model physics is observed. The measurement offers legacy result from unique Tevatron Collider data and provides more information about the top quark production and decays, about the properties of the heaviest elementary particle.},
doi = {10.2172/1347928},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2017},
month = {Sun Jan 01 00:00:00 EST 2017}
}

Thesis/Dissertation:
Other availability
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  • This thesis presents a measurement of the top quark polarization in themore » $$t\overline{t}$$ events produced in $$p\overline{p}$$ collisions at $$\sqrt{s}=1.96$$ TeV using data corresponding to 9.7 fb$$^{-1}$$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The final states used in the measurement contain one lepton and at least three jets. The polarization is measured using the angular distribution of leptons along three different axes: the beam axis, the helicity axis, and the transverse axis normal to the $$t\overline{t}$$ production plane. This is the first measurement of top quark polarization at the Tevatron Collider in lepton+jets final states, and the first measurement of transverse polarization in $$t\overline{t}$$ production. The polarization along the beam axis is combined with the previous result in the dilepton final states by the D0 experiment. The observed distributions are consistent with the Standard Model of nearly no polarization and no indication for beyond Standard Model physics is observed. The measurement offers legacy result from unique Tevatron Collider data and provides more information about the top quark production and decays, about the properties of the heaviest elementary particle.« less
  • Two alternative measurements of the t¯t production cross section at √s = 1.96 TeV in proton-antiproton collisions in the lepton+jets channel are presented. The t¯t production cross section is extracted by combining the kinematic event information in a multivariate discriminant. The measurement yields σ p¯p → t¯t + x = 5.13 -1.57 +1.76(stat) -1.10 +0.96(syst) ± 0.33 (lumi) pb in the muon+jets channel, using 229.1 pb -1, and in the combination with the electron+jets channel (226.3 pb -1) σ p¯p → t¯t + x = 6.60 -1.28 +1.37(stat) -1.11 +1.25(syst) ± 0.43 (lumi) pb. The second measurement presented reconstructs explicitlymore » secondary vertices to d lifetime b-tagging. The measurement combines the muon+jets and the electron+jets channel, using 158.4 pb -1 and 168.8 pb -1, respectively: σ p¯p → t¯t + x = 8.24 -1.25 +1.34(stat) -1.63 +1.89(syst) ± 0.54 (lumi) pb.« less
  • We present a measurement of forward-backward asymmetries in top-antitop quark pairs produced in proton-antiproton collisions decaying via the lepton+jets channel. Using data recorded by the D0 experiment at the Fermilab Tevatron collider and corresponding to an integrated luminosity of 5.4 fb -1, we measure the forward-backward asymmetry in top-antitop quark events to bemore » $$\left(9.2 \pm 3.7\right)\%$$, after background processes have been subtracted. After correcting for the effects of acceptance and detector reconstruction, we measure an asymmetry of $$\left(19.6 \pm 6.5\right)\%$$. In addition, we measure an acceptance-corrected asymmetry based on the lepton from top-antitop quark decay of $$\left(15.2 \pm 4.0\right)\%$$. We compare these results to predictions from the MC@NLO next-to-leading-order QCD simulation.« less
  • The mass of the top quark is a fundamental parameter of the Standard Model. Its precise knowledge yields valuable insights into unresolved phenomena in and beyond the Standard Model. A measurement of the top quark mass with the matrix element method in the lepton+jets final state in D0 Run II is presented. Events are selected requiring an isolated energetic charged lepton (electron or muon), significant missing transverse energy, and exactly four calorimeter jets. For each event, the probabilities to originate from the signal and background processes are calculated based on the measured kinematics, the object resolutions and the respective matrix elements. The jet energy scale is known to be the dominant source of systematic uncertainty. The reference scale for the mass measurement is derived from Monte Carlo events. The matrix element likelihood is defined as a function of both, m{sub top} and jet energy scale JES, where the latter represents a scale factor with respect to the reference scale. The top mass is obtained from a two-dimensional correlated fit, and the likelihood yields both the statistical and jet energy scale uncertainty. Using a dataset of 320 pb -1 of D0 Run II data, the mass of the top quark is measured to be: mmore » $$ℓ+jets\atop{top}$$ = 169.5 ± 4.4(stat. + JES)$$+1.7\atop{-1.6}$$(syst.) GeV; m$$e+jets\atop{top}$$ = 168.8 ± 6.0(stat. + JES)$$+1.9\atop{-1.9}$$(syst.) GeV; m$$μ+jets\atop{top}$$ = 172.3 ± 9.6(stat.+JES)$$+3.4\atop{-3.3}$$(syst.) GeV. The jet energy scale measurement in the ℓ+jets sample yields JES = 1.034 ± 0.034, suggesting good consistency of the data with the simulation. The measurement forecasts significant improvements to the total top mass uncertainty during Run II before the startup of the LHC, as the data sample will grow by a factor of ten and D0's tracking capabilities will be employed in jet energy reconstruction and flavor identification.« less
  • 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