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Title: Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration

Abstract

This thesis presents a measurement of the top quark mass obtained from p$$\bar{p}$$ collisions at √s = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. The measurement uses a matrix element integration method to calculate a t$$\bar{t}$$ likelihood, employing a Quasi-Monte Carlo integration, which enables us to take into account effects due to finite detector angular resolution and quark mass effects. We calculate a t$$\bar{t}$$ likelihood as a 2-D function of the top pole mass m t and Δ JES, where Δ JES parameterizes the uncertainty in our knowledge of the jet energy scale; it is a shift applied to all jet energies in units of the jet-dependent systematic error. By introducing Δ JES into the likelihood, we can use the information contained in W boson decays to constrain Δ JES and reduce error due to this uncertainty. We use a neural network discriminant to identify events likely to be background, and apply a cut on the peak value of individual event likelihoods to reduce the effect of badly reconstructed events. This measurement uses a total of 4.3 fb -1 of integrated luminosity, requiring events with a lepton, large E T, and exactly four high-energy jets in the pseudorapidity range |η| < 2.0, of which at least one must be tagged as coming from a b quark. In total, we observe 738 events before and 630 events after applying the likelihood cut, and measure m t = 172.6 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c 2, or m t = 172.6 ± 1.6 (tot.) GeV/c 2.

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
963775
Report Number(s):
FERMILAB-THESIS-2009-26
TRN: US0903275
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; B QUARKS; FERMILAB COLLIDER DETECTOR; FERMILAB TEVATRON; INTERMEDIATE BOSONS; LEPTONS; LUMINOSITY; MATRIX ELEMENTS; NEURAL NETWORKS; QUARKS; RESOLUTION; T QUARKS; Experiment-HEP

Citation Formats

Lujan, Paul Joseph. Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration. United States: N. p., 2009. Web. doi:10.2172/963775.
Lujan, Paul Joseph. Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration. United States. doi:10.2172/963775.
Lujan, Paul Joseph. 2009. "Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration". United States. doi:10.2172/963775. https://www.osti.gov/servlets/purl/963775.
@article{osti_963775,
title = {Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration},
author = {Lujan, Paul Joseph},
abstractNote = {This thesis presents a measurement of the top quark mass obtained from p$\bar{p}$ collisions at √s = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. The measurement uses a matrix element integration method to calculate a t$\bar{t}$ likelihood, employing a Quasi-Monte Carlo integration, which enables us to take into account effects due to finite detector angular resolution and quark mass effects. We calculate a t$\bar{t}$ likelihood as a 2-D function of the top pole mass mt and ΔJES, where ΔJES parameterizes the uncertainty in our knowledge of the jet energy scale; it is a shift applied to all jet energies in units of the jet-dependent systematic error. By introducing ΔJES into the likelihood, we can use the information contained in W boson decays to constrain ΔJES and reduce error due to this uncertainty. We use a neural network discriminant to identify events likely to be background, and apply a cut on the peak value of individual event likelihoods to reduce the effect of badly reconstructed events. This measurement uses a total of 4.3 fb-1 of integrated luminosity, requiring events with a lepton, large ET, and exactly four high-energy jets in the pseudorapidity range |η| < 2.0, of which at least one must be tagged as coming from a b quark. In total, we observe 738 events before and 630 events after applying the likelihood cut, and measure mt = 172.6 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2, or mt = 172.6 ± 1.6 (tot.) GeV/c2.},
doi = {10.2172/963775},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2009,
month =
}

Thesis/Dissertation:
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  • The discovery of the bottom quark in 1977 at the Tevatron Collider triggered the search for its partner in the third fermion isospin doublet, the top quark, which was discovered 18 years later in 1995 by the CDF and D=0 experiments during the Tevatron Run I. By 1990, intensive efforts by many groups at several accelerators had lifted to over 90 GeV=c2 the lower mass limit, such that since then the Tevatron became the only accelerator with high-enough energy to possibly discover this amazingly massive quark. After its discovery, the determination of top quark properties has been one of themore » main goals of the Fermilab Tevatron Collider, and more recently also of the Large Hadron Collider (LHC) at CERN. Since the mass value plays an important role in a large number of theoretical calculations on fundamental processes, improving the accuracy of its measurement has been at any time a goal of utmost importance. The present thesis describes in detail the contributions given by the candidate to the massive preparation work needed to make the new analysis possible, during her 8 months long stay at Fermilab.« 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
  • A measurement of the top quark mass in pmore » $$\bar{p}$$ collisions at √s = 1.96 TeV is presented. The analysis uses a template method, in which the overconstrained kinematics of the Lepton+Jets channel of the t$$\bar{t}$$ system are used to measure a single quantity, the reconstructed top quark mass, that is strongly correlated with the true top quark mass. in addition, the dijet mass of the hadronically decaying W boson is used to constrain in situ the uncertain jet energy scale in the CDF detector. Two-dimensional probability density functions are derived using a kernel density estimate-based machinery. Using 1.9 fb -1 of data, the top quark mass is measured to be 171.8$$+1.9\atop{-1.9}$$(stat.) ± 1.0(syst.)GeV/c 2.« less
  • We have measured the top quark mass with the dynamical likelihood method (DLM) using the CDF II detector at the Fermilab Tevatron. The Tevatron produces top and anti-top pairs in pp collisions at a center of mass energy of 1.96 TeV. The data sample used in this paper was accumulated from March 2002 through August 2003 which corresponds to an integrated luminosity of 162 pb -1.
  • We have measured the top quark mass with the dynamical likelihood method. The data corresponding to an integrated luminosity of 1.7fb -1 was collected in proton antiproton collisions at a center of mass energy of 1.96 TeV with the CDF detector at Fermilab Tevatron during the period March 2002-March 2007. We select tmore » $$\bar{t}$$ pair production candidates by requiring one high energy lepton and four jets, in which at least one of jets must be tagged as a b-jet. In order to reconstruct the top quark mass, we use the dynamical likelihood method based on maximum likelihood method where a likelihood is defined as the differential cross section multiplied by the transfer function from observed quantities to parton quantities, as a function of the top quark mass and the jet energy scale(JES). With this method, we measure the top quark mass to be 171.6 ± 2.0 (stat.+ JES) ± 1.3(syst.) = 171.6 ± 2.4 GeV/c 2.« less